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19-2712; Rev 0; 1/03
KIT ATION EVALU ABLE AVAIL
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
General Description Features
o Step-Up DC-to-DC Converter 95% Efficient 3.3V (Fixed) or 2.7V to 5.5V (Adjustable) Output Voltage o Step-Down DC-to-DC Converter Operate from Battery for 95% Efficient Buck Combine with Step-Up for 90% Efficient BuckBoost Adjustable Output Down to 1.25V o Three Auxiliary PWM Controllers o Up to 1MHz Operating Frequency o 1A Shutdown Mode o Internal Soft-Start Control o Overload Protection o Compact 32-Pin, 5mm x 5mm Thin QFN Package
MAX1565
The MAX1565 provides a complete power-supply solution for digital still and video cameras through the integration of ultra-high-efficiency step-up/step-down DC-to-DC converters along with three auxiliary step-up controllers. The MAX1565 is targeted for applications that use either 2 or 3 alkaline or NiMH batteries as well as those using a single lithium-ion (Li+) battery. The step-up DC-to-DC converter accepts inputs from 0.7V to 5.5V and regulates a resistor-adjustable output from 2.7V to 5.5V. It uses internal MOSFETs to achieve 95% efficiency. Adjustable operating frequency facilitates design for optimum size, cost, and efficiency. The step-down DC-to-DC converter can produce output voltages as low as 1.25V and also utilizes internal MOSFETs to achieve 95% efficiency. An internal softstart ramp minimizes surge current from the battery. The converter can operate from the step-up output providing buck-boost capability with up to 90% compound efficiency, or it can run directly from the battery if buckboost operation is not needed. The MAX1565 features auxiliary step-up controllers that power CCD, LCD, motor actuator, and backlight circuits. The device also features low-cost expandability by supplying power, an oscillator signal, and a reference to the MAX1801 SOT23 slave controller that supports step-up, SEPIC, and flyback configurations. The MAX1565 is available in a space-saving 32-pin thin QFN package.
Ordering Information
PART MAX1565ETJ TEMP RANGE -40C to +85C PIN-PACKAGE 32 Thin QFN
Pin Configuration
OUTSUB 26 COMP2
Applications
Digital Still Cameras Digital Video Cameras PDAs
TOP VIEW
FB2
GND
DL1
DL2
DL3
32 COMP1 1 2 3 4 5 6 7 8 9 ON1
31
30
29
28
27
25 24 COMP3 23 SDOK 22 OUTSUA 21 LXSU
Typical Operating Circuit
INPUT +0.7V TO +5.5V
FB1 PGNDA LXSD
MAX1565
STEP-UP STEP-DOWN ONSU ONSD ON1 ON2 0N3 AUX1 AUX2 AUX3 MAIN +3.3V CORE +1.5V MOTOR +5V CCD +15V/-7.5V LCD, LED +15V
INSD ONSD COMPSD FBSD
MAX1565
FB3 20 PGNDB 19 OSC 18 FBSEL1 17 FBSELSD 16 FBSELSU
10 ON2
11 ON3
12 ONSU
13 REF
14 FBSU
15 COMPSU
ON/OFF CONTROLS
5mm x 5mm THIN QFN
1
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
ABSOLUTE MAXIMUM RATINGS
OUTSU_, INSD, SDOK, ON_, FB_, FBSEL_ to GND ....................................................-0.3V to +6V PGND to GND .......................................................-0.3V to +0.3V DL_ to PGND...........................................-0.3V to OUTSU + 0.3V LXSU Current (Note 1) ..........................................................3.6A LXSD Current (Note 1) ........................................................2.25A REF, OSC, COMP_ to GND.....................-0.3V to OUTSU + 0.3V Continuous Power Dissipation (TA =+70C) 32-Pin Thin QFN (derate 22mW/C above +70C).............................................................1700mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: LXSU has internal clamp diodes to OUTSU and PGND, and LXSD has internal clamp diodes to INSD and PGND. Applications that forward bias these diodes should take care not to exceed the devices power dissipation limits.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VOUTSU = 3.3V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER GENERAL Input Voltage Range Minimum Startup Voltage Overload Protection Fault Interval Thermal Shutdown Thermal-Shutdown Hysteresis Shutdown Supply Current into OUTSU Step-Up DC-to-DC Supply Current into OUTSU Step-Up Plus 1 AUX Supply Current into OUTSU Step-Up Plus Step-Down Supply Current into OUTSU Reference Output Voltage Reference Load Regulation Reference Line Regulation OSC Discharge Trip Level OSC Discharge Resistance OSC Discharge Pulse Width OSC Frequency Step-Up Startup-to-Normal Operating Threshold Step-Up Startup-to-Normal Operating Threshold Hysteresis ROSC = 40k, COSC = 100pF STEP-UP DC-TO-DC CONVERTER Rising or falling edge (Note 4) 2.30 2.5 80 2.60 V mV ONSU = ONSD = ON1 = ON2 = ON3 = 0; OUTSU = 3.6V ONSU = 3.35V, FBSU = 1.5V (does not include switching losses) ONSU = ON_ = 3.35V, FBSU = 1.5V, FB_ = 1.5V (does not include switching losses) ONSU = ONSD = 3.35V, FBSU = 1.5V, FBSD = 1.5V (does not include switching losses) IREF = 20A 10A < IREF < 200A 2.7 < OUTSU < 5.5V Rising edge OSC = 1.5V, IOSC = 3mA 1.225 1.23 (Note 2) ILOAD < 1mA, TA = +25C, startup voltage tempco is -2300ppm/C (typ) (Note 3) 0.7 0.9 100,000 160 20 0.1 290 420 470 1.25 4.5 1.3 1.25 52 300 400 5 400 600 650 1.27 10 5 1.275 80 5.5 1.1 V V OSC cycles C C A A A A V mV mV V ns kHz CONDITIONS MIN TYP MAX UNITS
2
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
ELECTRICAL CHARACTERISTICS (continued)
(VOUTSU = 3.3V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER Step-Up Voltage Adjust Range FBSU Regulation Voltage OUTSU Regulation Voltage FBSU to COMPSU Transconductance FBSU Input Leakage Current Idle-ModeTM Trip Level Current-Sense Amplifier Transresistance Step-Up Maximum Duty Cycle OUTSU Leakage Current LXSU Leakage Current Switch On-Resistance N-Channel Current limit P-Channel Turn-Off Current Startup Current Limit Startup tOFF Startup Frequency FBSD Regulation Voltage OUTSD Regulation Voltage FBSD to COMPSD Transconductance FBSD Input Leakage Current Idle-Mode Trip Level Current-Sense Amplifier Transresistance LXSD Leakage Current Switch On-Resistance P-Channel Current Limit N-Channel Turn-Off Current Soft-Start Interval SDOK Output Low Voltage SDOK Operating Voltage Range FBSD = 0.4V; 0.1mA into SDOK pin 1.0 VLXSD = 5.5V, OUTSU = 5.5V VLXSD = 0V, OUTSU = 5.5V N-channel P-channel 0.7 FBSELSD = GND FBSD = COMPSD FBSD = 1.25V (Note 6) OUTSU = 1.8V (Note 5) OUTSU = 1.8V OUTSU = 1.8V 1.231 1.48 80 -100 110 FBSU = 1V VLX = 0V, OUTSU = 5.5V VLXSU = VOUT = 5.5V N-channel P-channel 1.6 80 FBSELSU = GND FBSU = COMPSU FBSU = 1.25V (Note 6) CONDITIONS MIN 2.7 1.231 3.296 80 -100 150 1.25 3.35 135 +1 200 0.3 85 0.01 0.01 95 150 2 20 800 700 200 1.25 1.5 135 +1 160 0.60 0.01 0.01 95 150 0.79 20 4096 0.002 0.1 5.5 20 20 150 250 1.0 1.269 1.52 185 +100 190 90 20 20 150 250 2.4 TYP MAX 5.5 1.269 3.404 185 +100 265 UNITS V V V S nA mA V/A % A A m A mA mA ns kHz V V S nA mA V/A A m A mA OSC cycles V V
MAX1565
STEP-DOWN DC-TO-DC CONVERTER
Idle Mode is a trademark of Maxim Integrated Products, Inc. _______________________________________________________________________________________ 3
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
ELECTRICAL CHARACTERISTICS (continued)
(VOUTSU = 3.3V, TA = 0C to +85C, unless otherwise noted.)
PARAMETER Maximum Duty Cycle FB_ Regulation Voltage FB_ to COMP_ Transconductance FB_ Input Leakage Current AUX1 Output Regulation Voltage DL_ Driver Resistance DL_ Drive Current Soft-Start Interval LOGIC INPUTS (ON_ , FBSEL_) Input Low Level 1.1V < OUTSU < 1.8V (ONSU only) 1.8V < OUTSU < 5.5V 1.1V < OUTSU < 1.8V (ONSU only) 1.8V < OUTSU < 5.5V FBSEL_ Input Leakage Current ON_ Impedance to GND FBSEL = 3.6V, OUTSU = 3.6V FBSEL = GND, OUTSU = 3.6V ON_ = 3.35V VOUTSU - 0.2 1.6 -100 -100 0 0 330 +100 +100 nA k 0.2 0.4 V FB_ = 1V FB_ = COMP_ FB_ = COMP_ FB_ = 1.25V FBSEL1 = GND, FB1 connected directly to AUX1 output Output high Output low Sourcing or sinking CONDITIONS MIN 80 1.231 80 -100 4.93 TYP 85 1.25 135 +1 5 3 2 0.5 4096 MAX 90 1.269 185 +100 5.07 10 5 UNITS % V S nA V A OSC cycles
AUXILIARY DC-TO-DC CONTROLLERS (AUX 1, 2, AND 3)
Input High Level
V
ELECTRICAL CHARACTERISTICS
(VOUTSU = 3.3V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER GENERAL Input Voltage Range Minimum Startup Voltage Shutdown Supply Current into OUTSU Step-Up DC-to-DC Supply Current into OUTSU Step-Up Plus 1 AUX Supply Current into OUTSU Step-Up Plus Step-Down Supply Current into OUTSU Reference Output Voltage Reference Load Regulation (Note 2) ILOAD < 1mA, TA = +25C, startup voltage tempco is -2300ppm/C (typ) (Note 3) ONSU = ONSD = ON1 = ON2 = ON3 = 0 OUTSU = 3.6V ONSU = 3.35V, FBSU = 1.5V (does not include switching losses) ONSU = ON_ = 3.35V, FBSU = 1.5V, FB_ = 1.5V (does not include switching losses) ONSU = ONSD = 3.35V, FBSU = 1.5V, FBSD = 1.5V (does not include switching losses) IREF = 20A 10A < IREF < 200A 1.23 0.7 5.5 1.1 5 400 600 650 1.27 10 V V A A A A V mV CONDITIONS MIN TYP MAX UNITS
4
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
ELECTRICAL CHARACTERISTICS (continued)
(VOUTSU = 3.3V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER Reference Line Regulation OSC Discharge Trip Level OSC Discharge Resistance Step-Up Startup-to-Normal Operating Threshold Step-Up Voltage Adjust Range FBSU Regulation Voltage OUTSU Regulation Voltage FBSU to COMPSU Transconductance FBSU Input Leakage Current Idle-Mode Trip Level Step-Up Maximum Duty Cycle OUTSU Leakage Current LXSU Leakage Current Switch On-Resistance N-Channel Current limit STEP-DOWN DC-TO-DC CONVERTER FBSD Regulation Voltage OUTSD Regulation Voltage FBSD to COMPSD Transconductance FBSD Input Leakage Current Idle-Mode Trip Level LXSD Leakage Current Switch On-Resistance P-Channel Current Limit SDOK Output Low Voltage SDOK Operating Voltage Range AUXILIARY DC-TO-DC CONTROLLERS (AUX 1, 2, AND 3) Maximum Duty Cycle FB_ Regulation Voltage FB_ = 1V FB_ = COMP_ 80 1.225 90 1.275 % V FBSD = 0.4V; 0.1mA into SDOK pin 1 FBSELSD = GND FBSD = COMPSD FBSD = 1.25V (Note 6) VLXSD = 5.5V, OUTSU = 5.5V VLXSD = 0V, OUTSU = 5.5V N-channel P-channel 0.7 1.225 1.47 80 -100 110 1.275 1.53 185 +100 195 20 20 150 250 1.0 0.1 5.5 V V S nA mA A m A V V FBSELSU = GND FBSU = COMPSU FBSU = 1.25V (Note 6) FBSU =1V VLX = 0V, OUTSU = 5.5V VLXSU = VOUT = 5.5V N-channel P-channel 1.6 Rising edge OSC = 1.5V, IOSC = 3mA CONDITIONS 2.7V < OUTSU < 5.5V 1.225 MIN TYP MAX 5 1.275 80 UNITS mV V
MAX1565
STEP-UP DC-TO-DC CONVERTER Rising or falling edge (Note 4) 2.30 2.7 1.225 3.283 80 -100 150 80 2.60 5.5 1.275 3.417 185 +100 275 90 20 20 150 250 2.4 V V V V S nA mA % A A m A
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5
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
ELECTRICAL CHARACTERISTICS (continued)
(VOUTSU = 3.3V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER FB_ to COMP_ Transconductance FB_ Input Leakage Current AUX1 Output Regulation Voltage DL_ Driver Resistance LOGIC INPUTS (ON_, FBSEL_) Input Low Level 1.1V < OUTSU < 1.8V (ONSU only) 1.8V < OUTSU < 5.5V 1.1V < OUTSU < 1.8V (ONSU only) 1.8V < OUTSU < 5.5V FBSEL_ Input Leakage Current FBSEL = 3.6V, OUTSU = 3.6V FBSEL = GND, OUTSU = 3.6V VOUTSU -0.2 1.6 -100 -100 +100 +100 nA 0.2 0.4 V FB_ = COMP_ FB_ = 1.25V FBSEL1 = GND, FB1 connected directly to AUX1 output Output high Output low CONDITIONS MIN 80 -100 4.90 TYP MAX 185 +100 5.10 10 5 UNITS S nA V
Input High Level
V
Note 2: Note 3: Note 4: Note 5: Note 6:
The IC is powered from the OUTSU output. Since the part is powered from OUTSU, a Schottky rectifier, connected from the input battery to OUTSU, is required for low-voltage startup. The step-up regulator operates in startup mode until this voltage is reached. Do not apply full load current during startup. The step-up current limit in startup refers to the LXSU switch current limit, not an output current limit. The idle-mode current threshold is the transition point between fixed-frequency PWM operation and idle-mode operation (where switching rate varies with load). The spec is given in terms of inductor current. In terms of output current, the idlemode transition varies with input/output voltage ratio and inductor value. For the step-up, the transition output current is approximately 1/3 the inductor current when stepping from 2V to 3.3V. For the step-down, the transition current in terms of output current is approximately 3/4 the inductor current when stepping down from 3.3V to 1.8V.
Typical Operating Characteristics
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
STEP-UP EFFICIENCY vs. LOAD CURRENT (5V OUTPUT)
MAX1565 toc01
STEP-UP EFFICIENCY vs. LOAD CURRENT (3.3V OUTPUT)
MAX1565 toc02
STEP-DOWN EFFICIENCY vs. LOAD CURRENT
90 80 EFFICIENCY (%) 70 60 50 40 30 20 INSD CONNECTED TO BATTERY VOUT = 1.5V DOES NOT INCLUDE CURRENT USED BY THE STEP-UP TO POWER THE IC 1 10 100 1000 VIN = 4.2V VIN = 3.6V VIN = 3V
MAX1565 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1 10 100 LOAD CURRENT (mA) VIN = 4V VIN = 3.6V VIN = 3V VIN = 2V VIN = 1.5V VOUT = 5V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1 10 100 LOAD CURRENT (mA) VOUT = 3.3V VIN = 3.6V VIN = 3V VIN = 2V VIN = 1.5V
100
10 0
1000
1000
LOAD CURRENT (mA)
6
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
BUCK-BOOST EFFICIENCY vs. LOAD CURRENT (3.3V OUTPUT, VOUTSU = 5V)
MAX1565 toc05 MAX1565 toc04
MAX1565
BUCK-BOOST EFFICIENCY vs. LOAD CURRENT (1.5V OUTPUT, VOUTSU = 3.3V)
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1 10 100 1000 LOAD CURRENT (mA) VOUTSD = 1.5V VOUTSU = 3.3V VIN = 3V VIN = 2V VIN = 1.5V 100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1
BUCK-BOOST EFFICIENCY vs. INPUT VOLTAGE (1.5V OUTPUT, VOUTSU = 3.3V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 IOUTSD = 250mA IOUTSD = 500mA IOUTSD = 100mA
MAX1565 toc06
100
VIN = 4.2V VIN = 3.6V VIN = 3V VIN = 2V VIN = 1.5V VOUTSD = 3.3V VOUTSU = 5V 10 100 1000
10 0 1.5
VOUTSD = 1.5V VOUTSU = 3.3V 2.0 2.5 3.0 3.5 4.0
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
BUCK-BOOST EFFICIENCY vs. INPUT VOLTAGE (3.3V OUTPUT, VOUTSU = 5V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) VOUTSD = 3.3V VOUTSU = 5V 50 60 IOUTSD = 500mA IOUTSD = 100mA IOUTSD = 250mA
MAX1565 toc07
BOOST AND BUCK-BOOST COMBINED EFFICIENCY vs. INPUT VOLTAGE
MAX1565 toc08
AUX_ EFFICIENCY vs. LOAD CURRENT (5V OUTPUT)
90 80 EFFICIENCY (%) 70 60 50 40 30 VIN = 3.6V VIN = 3V VIN = 2V VIN = 1.5V
MAX1565 toc09
100
100
100
90 EFFICIENCY (%)
80
70 VOUTSU = 3.3V, 200mA VOUTSD = 1.5V, 200mA EFF% = [(VSUISU) + (VSDISD)]/(VINIIN) 1.0 1.5 2.0 2.5 3.0 3.5
20 10 0 1 10 VOUTAUX_ = 5V 100 1000
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
NO-LOAD INPUT CURRENT vs. INPUT VOLTAGE (SWITCHING)
MAX1565 toc10
MINIMUM STARTUP VOLTAGE vs. LOAD CURRENT (OUTSU)
WITHOUT SCHOTTKY* MINIMUM STARTUP VOLTAGE (V) 3.0 2.5 2.0 1.5 1.0 0.5 0 *SCHOTTKY DIODE CONNECTED FROM IN TO OUTSU 0 300 600 900 1200 WITH SCHOTTKY*
MAX1565 toc11
3.5 3.0 INPUT CURRENT (mA) 2.5 2.0 1.5 1.0 0.5 0 1 2 3 INPUT VOLTAGE (V) 4 5 VOUTSD = 1.5V VOUTSU = 5V
STEP-UP BUCK-BOOST (STEP-UP AND STEP DOWN)
3.5
LOAD CURRENT (mA)
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7
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
REFERENCE VOLTAGE vs. TEMPERATURE
MAX1565 toc12
REFERENCE VOLTAGE vs. REFERENCE LOAD CURRENT
MAX1565 toc13
OSCILLATOR FREQUENCY vs. ROSC
800 OSCILLATOR FREQUENCY (kHz) 700 600 500 400 300 200 100 0 COSC = 470pF COSC = 220pF COSC = 100pF COSC = 47pF
MAX1565 toc14
1.249 1.248 REFERENCE VOLTAGE (V) 1.247 1.246 1.245 1.244 1.243 1.242 1.241 1.240 -50 -25 0 25 50 75
1.251 1.250 REFERENCE VOLTAGE (V) 1.249 1.248 1.247 1.246 1.245 1.244
900
100
0
50
100
150
200
250
1
10 ROSC (k)
100
1000
TEMPERATURE (C)
REFERENCE LOAD CURRENT (A)
AUX_ MAXIMUM DUTY CYCLE vs. FREQUENCY
MAX1565 toc15
STEP-UP STARTUP RESPONSE
MAX1565 toc16
88 87 MAXIMUM DUTY CYCLE (%) 86 85 84 83 82 81 80
WHEN THIS DUTY CYCLE IS EXCEEDED FOR 100,000 CLOCK CYCLES, THE MAX1565 SHUTS DOWN
0V
ONSU 5V/div OUTSU 2V/div IOUTSU 100mA/div
0V
0A COSC = 100pF 0A IIN VOUTSO = 3.3V 1A/div VIN = 2V 100s/div
0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (kHz)
BUCK-BOOST STARTUP RESPONSE
MAX1565 toc17
AUX_ STARTUP RESPONSE
MAX1565 toc18
0V
ONSD = ONSU 5V/div OUTSU 1V/div
0V
ON1 5V/div OUT1 2V/div
OUTSD 500mA/div 0V 0V 0A 4ms/div VOUTSU = 3.3V VOUTSD = 1.5V VIN = 2.5V IOUTSD 200mA/div
0V IOUT1 200mA/div
0A 2ms/div
VOUT1 = 5V VIN = 2.5V
8
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
MAX1565
STEP-UP LOAD TRANSIENT RESPONSE
MAX1565 toc19
STEP-DOWN LOAD TRANSIENT RESPONSE
MAX1565 toc20
IOUTSU 200mA/div 0A 0A 0V VOUTSU = 3.3V VIN = 2.5V 400s/div VOUTSU AC-COUPLED 100mV/div 0V VOUTSD = 1.5V VOUTSU = 3.3V VIN = 2.5V 400s/div
IOUTSD 100mA/div
VOUTSD AC-COUPLED 50mV/div
Pin Description
PIN 1 NAME COMP1 FUNCTION Auxiliary Controller 1 Compensation Node. Connect a series RC from COMP1 to GND to compensate the control loop. COMP1 is actively driven to GND in shutdown and thermal limit. Auxiliary Controller 1 Feedback Input. For 5V output, short FBSEL1 to GND and connect FB1 to the output voltage. For other output voltages, connect FBSEL1 to OUTSU and connect a resistive voltage-divider from the step-up converter output to FB1 to GND. The FB1 feedback threshold is then 1.25V. This pin is high impedance in shutdown. Power Ground. Connect PGNDA and PGNDB together and to GND with short trace as close to the IC as possible. Step-Down Converter Power-Switching Node. Connect LXSD to the step-down converter inductor. LXSD is the drain of the P-channel switch and N-channel synchronous rectifier. LXSD is high impedance in shutdown. Step-Down Converter Input. INSD can connect to OUTSU, effectively making OUTSD a buck-boost output from the battery. Bypass to GND with a 1F ceramic capacitor if connected to OUTSU. INSD may also be connected to the battery, but should not exceed OUTSU by more than a Schottky diode forward voltage. Bypass INSD with a 10F ceramic capacitor when connecting to the battery input. A 10k internal resistance connects OUTSU and INSD. Step-Down Converter On/Off Control Input. Drive ONSD high to turn on the step-down converter. This pin has an internal 330k pulldown resistor. ONSD does not start until OUTSU is in regulation.
2
FB1
3
PGNDA
4
LXSD
5
INSD
6
ONSD
7
Step-Down Converter Compensation Node. Connect a series RC from COMPSD to GND to compensate the COMPSD control loop. COMPSD is pulled to GND in normal shutdown and during thermal shutdown (see the StepDown Compensation section).
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9
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
Pin Description (continued)
PIN 8 NAME FBSD FUNCTION Step-Down Converter Feedback Input. For a 1.5V output, short FBSELSD to GND and connect FBSD to OUTSD. For other voltages, short FBSELSD to OUTSU and connect a resistive voltage-divider from OUTSD to FBSD to GND. The FBSD feedback threshold is 1.25V. This pin is high impedance in shutdown. Auxiliary Controller 1 On/Off Control Input. Drive ON1 high to turn on. This pin has an internal 330k pulldown resistor. ON1 cannot start until OUTSU is in regulation. Auxiliary Controller 2 On/Off Control Input. Drive ON2 high to turn on. This pin has an internal 330k pulldown resistor. ON2 cannot start until OUTSU is in regulation. Auxiliary Controller 3 On/Off Control Input. Drive ON3 high to turn on. This pin has an internal 330k pulldown resistor. ON3 cannot start until OUTSU is in regulation. Step-Up Converter On/Off Control. Drive ONSU high to turn on the step-up converter. All other control pins are locked out until 2ms after the step-up output has reached its final value. This pin has an internal 330k resistance to GND. Reference Output. Bypass REF to GND with a 0.1F or greater capacitor. The maximum allowed load on REF is 200A. REF is actively pulled to GND when all converters are shut down. Step-Up Converter Feedback Input. To regulate OUTSU to 3.35V, connect FBSELSU to GND. FBSU may be connected to OUTSU or GND. For other output voltages, connect FBSELSU to OUTSU and connect a resistive voltage-divider from OUTSU to FBSU to GND. The FBSU feedback threshold is 1.25V. This pin is high impedance in shutdown.
9 10 11
ON1 ON2 ON3
12
ONSU
13
REF
14
FBSU
15
Step-Up Converter Compensation Node. Connect a series RC from COMPSU to GND to compensate the COMPSU control loop. COMPSD is pulled to GND in normal shutdown and during thermal shutdown (see the StepDown Compensation section). Step-Up Feedback Select Pin. With FBSELSU = GND, OUTSU regulates to 3.35V. With FBSELSU = OUTSU, FBSU regulates to a 1.25V threshold for use with external feedback resistors. This pin is high impedance in shutdown. Step-Down Feedback Select Pin. With FBSELSD = GND, FBSD regulates to 1.5V. With FBSELSD = OUTSU, FBSD regulates to 1.25V for use with external feedback resistors. This pin is high impedance in shutdown. Auxiliary Controller 1 Feedback Select Pin. With FBSEL1 = GND and FB1 regulates to 5V. With FBSEL1 = OUTSU, FB1 regulates to 1.25V for use with external feedback resistors. This pin is high impedance in shutdown. Oscillator Control. Connect a timing capacitor from OSC to GND and a timing resistor from OSC to OUTSU to set the oscillator frequency between 100kHz and 1MHz. This pin is high impedance in shutdown. Power Ground. Connect PGNDA and PGNDB together and to GND with short trace as close to the IC as possible. Step-Up Converter Power-Switching Node. Connect LXSU to the step-up converter inductor. LXSU is high impedance in shutdown. Step-Up Converter Output. OUTSUA is the power output of the step-up converter. Connect OUTSUA to OUTSUB at the IC. This open-drain output goes high impedance when the step-down has successfully completed soft-start.
16
FBSELSU
17
FBSELSD
18
FBSEL1
19 20 21 22 23
OSC PGNDB LXSU OUTSUA SDOK
10
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Pin Description (continued)
PIN 24 25 26 27 28 29 30 31 NAME COMP3 FB3 OUTSUB DL3 DL2 DL1 GND COMP2 FUNCTION Auxiliary Controller 3 Compensation Node. Connect a series resistor-capacitor from COMP3 to GND to compensate the control loop. COMP3 is actively driven to GND in shutdown and thermal limit. Auxiliary Controller 3 Feedback Input. Connect a resistive voltage-divider from the output voltage to FB3 to GND. The FB3 feedback threshold is 1.25V. This pin is high impedance in shutdown. Step-Up Converter Output. OUTSUB powers the MAX1565 and is the sense input when FBSELSU is GND and the output is 3.3V. Connect OUTSUA to OUTSUB. Auxiliary Controller 3 Gate-Drive Output. Connect the gate of an N-channel MOSFET to DL3. DL3 swings from GND to OUTSU and supplies up to 500mA. DL3 is driven to GND in shutdown and thermal limit. Auxiliary Controller 2 Gate-Drive Output. Connect the gate of an N-channel MOSFET to DL2. DL2 swings from GND to OUTSU and supplies up to 500mA. DL2 is driven to GND in shutdown and thermal limit. Auxiliary Controller 1 Gate-Drive Output. Connect the gate of an N-channel MOSFET to DL1. DL1 swings from GND to OUTSU and supplies up to 500mA. DL1 is driven to GND in shutdown and thermal limit. Quiet Ground. Connect GND to PGND as close to the IC as possible. Auxiliary Controller 2 Compensation Node. Connect a series resistor-capacitor from COMP2 to GND to compensate the control loop. COMP2 is actively driven to GND in shutdown and thermal limit. Auxiliary Controller 2 Feedback Input. Connect a resistive voltage-divider from the output voltage to FB2 to GND to set the output voltage. The FB2 feedback threshold is 1.25V. This pin is high impedance in shutdown. Exposed Underside Metal Pad. This pad must be soldered to the PC board to achieve package thermal and mechanical ratings. The exposed pad is electrically connected to GND.
MAX1565
32 Exposed Pad
FB2
EP
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
VIN +1.5V TO +4.2V 20F 2H T1 -7.5V 20mA -CCD BIAS 1F
MAX1565
5V 500mA 20F AUX1 DL1 V-MODE STEP-UP PWM FB1 AUX3 V-MODE DL3 STEP-UP PWM FB3 90.9k REF 0.1 F TO OUTSU 36.5k OSC 100pF OUTSUB COMPSU COMPSD COMP1 COMP2 CURRENTCOMP3 MODE STEP-UP 10k 0.01F 1000pF 1000pF ONSU ONSD ON1 ON2 ON3 FBSELSU FBSELSD FBSEL1 GND PGNDB FBSU INSD 10F CURRENTMODE STEPDOWN LXSD 4.7H 22F PGNDA FBSD SDOK +1.5V 350mA CORE TO VIN TO STEP-DOWN DIRECT FROM BATTERY OUTSUA 47F LXSU 3.3H TO VIN 1F 3.35V 600mA MAIN SYSTEM +1.25V REF AUX2 V-MODE DL2 STEP-UP PWM 4.7H TO VIN 1F +15V 100mA LCD 1M 90.9k 1M +15V 20mA +CCD BIAS 1F
10F FB2
47k 25k 20k 6800pF 3300pF 10k
Figure 1. Typical Application Circuit 12 ______________________________________________________________________________________
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
VOUTSU 2.35V ONSU VREF REFOK 1V ONSU FLTALL 100,000 CLOCK CYCLE FAULT TIMER FAULT IN CLK OUTSUB OSC REF 300ns ONE-SHOT TO INTERNAL POWER DIE OVER TEMP INTERNAL POWER OK NORMAL MODE STARTUP OSCILLATOR
1.25V REFERENCE
REF
GND
COMPSU OUTSUA FBSU FAULT CURRENTMODE DC-TO-DC STEP-UP TO VREF LXSU
STEP-UP TIMER DONE (SUSSD)
STARTUP TIMER
PGND ONSU FLTALL
COMPSD INSD FBSD FAULT CURRENTMODE DC-TO-DC STEP-DOWN TO VREF LXSD
SOFT-START RAMP GENERATOR ONSD SUSSD FLTALL
PGND SDOK
COMP_ FB_
FAULT ONE OF 3 VOLTAGE-MODE DC-TO-DC CONTROLLERS AUX_
DL_
SOFT-START RAMP GENERATOR ON_
TO VREF
SUSSD FLTALL
Figure 2. MAX1565 Functional Diagram ______________________________________________________________________________________ 13
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
Detailed Description
The MAX1565 is a complete digital still camera powerconversion IC. It can accept input from a variety of sources including single-cell Li+ batteries, 2-cell alkaline or NiMH batteries, as well as systems designed to accept both battery types. The MAX1565 includes five DC-to-DC converter channels to generate all required voltages: 1) Synchronous rectified step-up DC-to-DC converter with on-chip MOSFETs--This typically supplies 3.3V for main system power. 2) Synchronous rectified step-down DC-to-DC converter with on-chip MOSFETs--Powering the stepdown from the step-up output provides efficient (up to 90%) buck-boost functionality that supplies a regulated output when the battery voltage is above or below the output voltage. The step-down can also be powered from the battery. 3) Auxiliary DC-to-DC Controller 1--Typically used for 5V output for motor, strobe, or other functions as required. 4) Auxiliary DC-to-DC Controller 2--Typically supplies LCD bias voltages with either a multi-output flyback transformer, or boost converter with chargepump inverter. Alternately may power white LEDs for LCD backlighting. 5) Auxiliary DC-to-DC Controller 3--Typically supplies CCD bias voltages with either a multi-output flyback transformer, or boost converter with chargepump inverter. The MAX1565 can also operate with MAX1801 slave DCto-DC controllers if additional DC-to-DC converter channels are required. All MAX1565 DC-to-DC converter channels employ fixed-frequency PWM operation. In addition to multiple DC-to-DC channels, the MAX1565 also includes overload protection, soft-start circuitry, adjustable PWM operating frequency, and a power-OK (POK) output to signal when the step-down converter output voltage (for CPU core) is in regulation. The step-up is a current-mode PWM. An error signal (at COMPSU) represents the difference between the feedback voltage and the reference. The error signal programs the inductor current to regulate the output voltage. At light loads (under 75mA when boosting from 2V to 3.3V), efficiency is enhanced by an idle mode in which switching occurs only as needed to service the load. In this mode, the inductor current peak is limited to typically 200mA for each pulse.
Step-Down DC-to-DC Converter
The step-down DC-to-DC converter channel is optimized for generating output voltages down to 1.25V. Lower output voltages can be set by adding an additional resistor (see the Applications Information section). An internal switch and synchronous rectifier allow conversion efficiencies as high as 95% while reducing both circuit size and the number of external components. Under moderate to heavy loading, the converter operates in a low-noise PWM mode with constant frequency. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. The step-down is a current-mode PWM. An error signal (at COMPSD) represents the difference between the feedback voltage and the reference. The error signal programs the inductor current to regulate the output voltage. At light loads (under 120mA), efficiency is enhanced by an idle mode in which switching occurs only as needed to service the load. In this mode, the inductor current peak is limited to 150mA (typ) for each pulse. The step-down remains inactive until the step-up DCto-DC is in regulation. This means that the step-down DC-to-DC on/off pin (ONSD) is overridden by ONSU. The soft-start sequence for the step-down begins 1024 OSC cycles after the step-up output is in regulation. If the step-up, step-down, or any of the auxiliary controllers remains faulted for 200ms, all channels turn off. The step-down also features an open-drain SDOK output that goes low when the output is in regulation. Buck-Boost Operation The step-down input can be powered from the output of the step-up. By cascading these two channels, the stepdown output can maintain regulation even as the battery voltage falls below the step-down output voltage. This is especially useful when trying to generate 3.3V from 1-cell Li+ inputs, or 2.5V from 2-cell alkaline or NiMH inputs, or when designing a power supply that must operate from both Li+ and alkaline/NiMH inputs. Compound efficiencies of up to 90% can be achieved when the step-up and step-down are operated in series.
Step-Up DC-to-DC Converter
The step-up DC-to-DC converter channel generates a 2.7V to 5.5V output voltage range from a 0.9V to 5.5V battery input voltage. An internal switch and synchronous rectifier allow conversion efficiencies as high as 95% while reducing both circuit size and the number of external components. Under moderate to heavy loading, the converter operates in a low-noise PWM mode with constant frequency. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered.
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Note that the step-up output supplies both the step-up load and the step-down input current when the stepdown is powered from the step-up. The step-down input current reduces the available step-up output current for other loads. Direct Battery Step-Down Operation The step-down converter can also be operated directly from the battery as long as the voltage at INSD does not exceed OUTSU by more than a Schottky diode forward voltage. When using this connection, connect a Schottky diode from the battery input to OUTSU. There is also an internal 10k resistance from OUTSU to INSD, which adds a small additional current drain (of approximately (V OUTSU - V INSD)/10k from OUTSU when INSD is not connected directly to OUTSU. Step-down direct battery operation improves efficiency for the step-down output (up to 95%), but limits the upper limit of the output voltage to 200mV less than the minimum battery voltage. In 1-cell Li+ designs (with a 2.7V min), the output can be set up to 2.5V. In 2-cell alkaline or NiMH designs, the output may be limited to 1.5V or 1.8V, depending on the minimum allowed cell voltage. The step-down can only be briefly operated in dropout since the MAX1565 fault protection detects the out-ofregulation condition and activates after 100,000 OSC cycles, or 200ms at 500kHz. At that point, all MAX1565 channels shut down.
Auxiliary DC-to-DC Controllers
The three auxiliary controllers operate as fixed-frequency voltage-mode PWM controllers. They do not have internal MOSFETs, so output power is determined by external components. The controllers regulate output voltage by modulating the pulse width of the DL_ drive signal to an external N-channel MOSFET switch. Figure 3 shows a functional diagram of an AUX controller channel. A sawtooth oscillator signal at OSC governs timing. At the start of each cycle, DL_ goes high, turning on the external N-FET switch. The switch then turns off when the internally level-shifted sawtooth rises above COMP_ or when the maximum duty cycle is exceeded. The switch remains off until the start of the next cycle. A transconductance error amplifier forms an integrator at COMP_ so that DC high-loop gain and accuracy can be maintained. The auxiliary controllers do not start until the step-up DC-to-DC output is in regulation. If the step-up, stepdown, or any of the auxiliary controllers remains faulted for 100,000 OSC cycles, then all MAX1565 channels latch off.
MAX1565
FB
COMP R LEVEL SHIFT REFI REF 0.85 REF CLK OSC SOFTSTART* S Q DL_
*SOFT-START RAMPS REFI FROM 0V TO VREF IN 4096 CLOCK CYCLES.
FAULT PROTECTION
ENABLE
Figure 3. PWM Auxiliary Controller Functional Diagram ______________________________________________________________________________________ 15
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Maximum Duty Cycle The MAX1565 auxiliary PWM controllers have a guaranteed maximum duty cycle of 80%. That is to say that all controllers can achieve at least 80% and typically reach 85%. In boost designs that employ continuous current, the maximum duty cycle limits the boost ratio such that: 1 - VIN/VOUT 80% With discontinuous inductor current, no such limit exists for the input/output ratio since the inductor has time to fully discharge before the next cycle begins.
MAX1565
Reference
The MAX1565 has an internal 1.250V reference. Connect a 0.1F ceramic bypass capacitor from REF to GND within 0.2in (5mm) of the REF pin. REF can source up to 200A and is enabled whenever ONSD is high and OUTSD is above 2.5V. The auxiliary controllers and MAX1801 slave controllers (if connected) each sink up to 30A REF current during startup. If the application requires that REF be loaded beyond 200A, it may be buffered with a unity-gain amplifier or op amp.
Oscillator
All MAX1565 DC-to-DC converter channels employ fixed-frequency PWM operation. The operating frequency is set by an RC network at the OSC pin. The range of usable settings is 100kHz to 1MHz. When MAX1801 slave controllers are added, they operate at the same frequency set by OSC. The oscillator uses a comparator, a 300ns one-shot, and an internal N-FET switch in conjunction with an external timing resistor and capacitor (Figure 4). When the switch is open, the capacitor voltage exponentially approaches the step-up output voltage from zero with a time constant given by the ROSCCOSC product. The comparator output switches high when the capacitor voltage reaches VREF (1.25V). In turn, the one-shot activates the internal MOSFET switch to discharge the capacitor within a 300ns interval, and the cycle repeats. Note that the oscillation frequency changes as the main output voltage ramps upward following startup. The oscillation frequency is constant once the main output is in regulation.
Master/Slave Configurations
The MAX1565 supports MAX1801 slave PWM controllers that obtain input power, a voltage reference, and an oscillator signal directly from the MAX1565 master. The master/slave configuration allows channels to be easily added and minimizes system cost by eliminating redundant circuitry. The slaves also control the harmonic content of noise since their operating frequency is synchronized to that of the MAX1565 master converter. A MAX1801 connection to the MAX1565 is shown in Figure 11.
Fault Protection
The MAX1565 has robust fault and overload protection. After power-up, the device is set to detect an out-of regulation state that could be caused by an overload or short. If any DC-to-DC converter channel (step-up, step-down, or any of the auxiliary controllers) remains faulted for 100,000 clock cycles, then ALL outputs latch off until the step-up DC-to-DC converter is reinitialized by the ONSU pin, or by cycling of input power. The fault-detection circuitry for any channel is disabled during its initial turn-on soft-start sequence. Note that output of the step-up, or that of any auxiliary channel set up in boost configuration, does not fall to 0V during shutdown or fault. This is due to the current path from the battery to the output that remains even when the channel is off. This path exists through the boost inductor and the synchronous rectifier body diode. An auxiliary boost channel falls to the input voltage minus the rectifier drop during fault and shutdown. OUTSU falls to the input voltage minus the synchronous rectifier body diode drop during shutdown, and also during fault if the input voltage exceeds 2.5V. If the input voltage is less than 2.5V, OUTSU remains at 2.5V due to operation of the startup oscillator, but can source only limited current.
VOUTSU
ROSC OSC COSC VREF (1.25V) 300ns ONE-SHOT
MAX1565
Figure 4. Master Oscillator
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Low-Voltage Startup Oscillator
The MAX1565 internal control and reference-voltage circuitry receive power from OUTSU and do not function when OUTSU is less than 2.5V. To ensure low-voltage startup, the step-up employs a low-voltage startup oscillator that activates at 0.9V. The startup oscillator drives the internal N-channel MOSFET at LXSU until OUTSU reaches 2.5V, at which point voltage control is passed to the current-mode PWM circuitry. Once in regulation, the MAX1565 operates with inputs as low as 0.7V since internal power for the IC is supplied by OUTSU. At low input voltages, the MAX1565 can have difficulty starting into heavy loads.
MAX1565
Table 1. Voltage Setting Summary
CHANNEL FB_ FBSU FBSD FB1 FB2 FB2 FB THRESHOLD (FBSEL_ LOW) 3.35V 1.5V 5V Always 1.25V (FBSEL is not provided for these channels) 1.25V FB THRESHOLD (FBSEL_ HIGH)
Soft-Start
The MAX1565 step-down and AUX_ channels feature a soft-start function that limits inrush current and prevents excessive battery loading at startup by ramping the output voltage to the regulation voltage. This is achieved by increasing the internal reference inputs to the controller transconductance amplifiers from 0V to the 1.25V reference voltage over 4096 oscillator cycles (8ms at 500kHz) when initial power is applied or when a channel is enabled. Soft-start is not included in the step-up converter in order to avoid limiting startup capability with loading.
The capacitor voltage is then given time (t2 = 300ns) to discharge. The oscillator frequency is fOSC = 1/(t1 + t2) fOSC can operate from 100kHz to 1MHz. Choose COSC between 47pF and 470pF. Determine ROSC from the equation: ROSC = (300ns - 1/fOSC)/(COSC ln [1 - 1.25/VOUTSU]) See the Typical Operating Characteristics for fOSC versus ROSC using different values of COSC.
Setting Output Voltages
The MAX1565 step-up/step-down converters and the AUX1 controllers have both factory-set and adjustable output voltages. These are selected by FBSEL_ for the appropriate channel. When FBSEL_ is low, the channel output regulates at its preset voltage. When FBSEL_ is high, the channel regulates FB_ at 1.25V for use with external feedback resistors. When setting the voltage for auxiliary channels 2 and 3, or when using external feedback at FBSU, FBSD, or FB1, connect a resistive voltage-divider from the output voltage to the corresponding FB_ input. The FB_ input bias current is less than 100nA, so choose the low-side (FB_to-GND) resistor (RL), to be 100k or less. Then calculate the high-side (output-to-FB_) resistor (RH) using: RH = RL [(VOUT/1.25) - 1]
Shutdown
The step-up converter is activated with a high input at ONSU. The step-down and auxiliary DC-to-DC converters 1, 2, and 3 activate with a high input at ONSD, ON1, ON2, and ON3, respectively. The auxiliary controllers and step-down cannot be activated until OUTSU is in regulation. For automatic startup, connect ON_ to OUTSU or a logic level greater than 1.6V.
Design Procedure
Setting the Switching Frequency
Choose a switching frequency to optimize external component size or circuit efficiency for any particular MAX1565 application. Typically, switching frequencies between 300kHz and 600kHz offer a good balance between component size and circuit efficiency. Higher frequencies generally allow smaller components and lower frequencies give better conversion efficiency. The switching frequency is set with an external timing resistor (ROSC) and capacitor (COSC). At the beginning of a cycle, the timing capacitor charges through the resistor until it reaches VREF. The charge time, t1, is: t1 = -ROSCCOSC ln [1 - 1.25/VOUTSU]
General Filter Capacitor Selection
The input capacitor in a DC-to-DC converter reduces current peaks drawn from the battery, or other input power source, and reduces switching noise in the controller. The impedance of the input capacitor at the switching frequency should be less than that of the input source so that high-frequency switching currents do not pass through the input source.
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
The output capacitor keeps output ripple small and ensures control-loop stability. The output capacitor must also have low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are suitable, with ceramic exhibiting the lowest ESR and high-frequency impedance. Output ripple with a ceramic output capacitor is approximately: VRIPPLE = IL(PEAK) [1/(2 fOSC COUT)] If the capacitor has significant ESR, the output ripple component due to capacitor ESR is: VRIPPLE(ESR) = IL(PEAK) ESR Output capacitor specifics are also discussed in the Step-Up Compensation section and the Step-Down Compensation section. Step-Up Compensation The inductor and output capacitor are usually chosen first in consideration of performance, size, and cost. The compensation resistor and capacitor are then chosen to optimize control-loop stability. In some cases it may help to readjust the inductor or output capacitor value to get optimum results. For typical designs, the component values in the circuit of Figure 1 yield good results. The step-up converter employs current-mode control, thereby simplifying the control-loop compensation. When the converter operates with continuous inductor current (typically the case), a right-half-plane zero (RHPZ) appears in the loop-gain frequency response. To ensure stability, the control-loop gain should crossover (drop below unity gain) at a frequency (fC) much less than that of the right-half-plane zero. The relevant characteristics for step-up channel compensation are: 1) Transconductance (from FBSU to COMPSU), gmEA (135S) 2) Current-sense amplifier transresistance, R CS , (0.3V/A) 3) Feedback regulation voltage, VFB (1.25V) 4) Step-up output voltage, VSUOUT, in V 5) Output load equivalent resistance, R LOAD , in = VSUOUT/ILOAD The key steps for step-up compensation are: 1) Place fC sufficiently below the RHPZ and calculate CC. 2) Select RC based on the allowed load-step transient. RC sets a voltage delta on the COMP pin that corresponds to load current step. 3) Calculate the output filter capacitor (C OUT ) required to allow the RC and CC selected. 4) Determine if CP is required (if calculated to be > 10pF). For continuous conduction, the right-plane zero frequency (fRHPZ) is given by: fRHPZ = VOUTSU (1 - D)2 / (2 L ILOAD) where D = the duty cycle = 1 - (VIN/VOUT), L is the inductor value, and ILOAD is the maximum output current. Typically target crossover (fC) for 1/6 the RHPZ. For example, if we assume VIN = 2V, VOUT = 3.35V, and I OUT = 0.5A, then R LOAD = 6.7. If we select L = 3.3H then: fRHPZ = 3.35 (2/3.35)2 / (2 x 4.7 x 10-6 x 0.5) = 115kHz
Step-Up Component Selection
The external components required for the step-up are an inductor, input and output filter capacitor, and compensation RC. Typically, the inductor is selected to operate with continuous current for best efficiency. An exception might be if the step-up ratio, (VOUT/VIN), is greater than 1/(1 - DMAX), where DMAX is the maximum PWM duty factor of 80%. When using the step-up channel to boost from a low input voltage, loaded startup is aided by connecting a Schottky diode from the battery to OUTSU. See the Minimum Startup Voltage vs. Load Current graph in the Typical Operating Characteristics. Step-Up Inductor In most step-up designs, a reasonable inductor value (LIDEAL) can be derived from the following equation, which sets continuous peak-to-peak inductor current at one-half the DC inductor current: LIDEAL = [2 VIN(MAX) D(1 - D)] / (IOUT fOSC) where D is the duty factor given by: D = 1 - (VIN / VOUT) Given LIDEAL, the consistent peak-to-peak inductor current is 0.5 I OUT /(1 - D). The peak inductor current, IIND(PK) = 1.25 IOUT / (1 - D). Inductance values smaller than L IDEAL can be used to reduce inductor size. However, if much smaller values are used, the inductor current rises and a larger output capacitance may be required to suppress output ripple.
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Choose fC = 20kHz. Calculate CC: CC = (VFB/VOUT)(RLOAD/RCS)(gm/2 fC)(1 - D) = (1.25/3.35)(6.7/0.3) x (135S/(6.28 x 20kHz) (2/3.35) = 5.35nF Choose 6.8nF. Now select RC such that transient droop requirements are met. For example, if 4% transient droop is allowed, the input to the error amplifier moves 0.04 x 1.25V, or 50mV. The error amp output drives 50mV x 135S, or 6.75A, across RC to provide transient gain. Since the current-sense transresistance is 0.3V/A, the value of RC that allows the required load step swing: RC = 0.3 IIND(PK)/6.75A In a step-up DC-to-DC converter, if LIDEAL is used, output current relates to inductor current by: IIND(PK) = 1.25 IOUT/(1 - D) = 1.25 IOUT VOUT/VIN Thus, for a 400mA output load step with VIN = 2V and VOUT = 3.35V: RC = [1.25(0.3 x 0.4 x 3.35)/2)]/6.75A = 37k Note that the inductor does not limit the response in this case since it can ramp at 2V/3.3H, or 606mA/s. The output filter capacitor is then chosen so that the COUT RLOAD pole cancels the RC CC zero: COUT RLOAD = RCCC For example: COUT = 37k x 6.8nF/6.7 = 37.5F Since a reasonable value for COUT is 47F rather than 37.5, choose 47F and rescale RC: RC = 47F x 6.7/6.8nF = 46.3k which provides a slightly higher transient gain and consequently less transient droop than previously selected. If the output filter capacitor has significant ESR, a zero occurs at: ZESR = 1/(2 COUT RESR) If ZESR > fC, it can be ignored, as is typically the case with ceramic output capacitors. If ZESR is less than fC, it should be cancelled with a pole set by capacitor CP connected from COMPSU to GND: CP = COUT RESR/RC If CP is calculated to be < 10pF, it can be omitted.
Step-Down Component Selection
Step-Down Inductor The external components required for the step-down are an inductor, input and output filter capacitors, and compensation RC network. The MAX1565 step-down converter provides best efficiency with continuous inductor current. A reasonable inductor value (LIDEAL) can be derived from: LIDEAL = 2 (VIN) D (1 - D)/(IOUT fOSC) which sets the peak-to-peak inductor current at 1/2 the DC inductor current. D is the duty cycle: D = VOUT/VIN Given LIDEAL, the peak-to-peak inductor current variation is 0.5 IOUT. The absolute peak inductor current is 1.25 IOUT. Inductance values smaller than LIDEAL can be used to reduce inductor size. However, if much smaller values are used, inductor current rises and a larger output capacitance may be required to suppress output ripple. Larger values than LIDEAL can be used to obtain higher output current, but with typically larger inductor size. Step-Down Compensation The relevant characteristics for step-down compensation are: 1) Transconductance (from FBSD to COMPSD), gmEA (135S) 2) Step-down slope compensation pole, P SLOPE = VIN / (L) 3) Current-sense amplifier transresistance, R CS , (0.6V/A) 4) Feedback regulation voltage, VFB (1.25V) 5) Step-down output voltage, VSD, in V 6) Output load equivalent resistance, R LOAD , in = VOUTSD/ILOAD The key steps for step-down compensation are: 1) Set the compensation RC zero to cancel the RLOAD COUT pole. 2) Set the loop crossover below the lower of 1/5 the slope compensation pole, or 1/5 the switching frequency. If we assume VIN = 3.35V, VOUT = 1.5V, and IOUT = 350mA, then RLOAD = 4.3.
MAX1565
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
If we select L = 4.7H and fOSC = 440kHz, PSLOPE = VIN/(L) = 214kHz, so choose fC = 40kHz and calculate CC: CC = (VFB/VOUT)(RLOAD/RCS)(gm/2 fC) = (1.25/1.5)(4.3/0.6) x (135S/(6.28 x 40kHz) = 3.2nF Choose 3.3nF. Now select RC such that transient droop requirements are met. For example, if 4% transient droop is allowed, the input to the error amplifier moves 0.04 x 1.25V, or 50mV. The error amp output drives 50mV x 135S, or 6.75A across RC to provide transient gain. Since the current-sense transresistance is 0.6V/A, the value of RC that allows the required load step swing: RC = 0.6 IIND(PK)/6.75A In a step-down DC-to-DC converter, if LIDEAL is used, output current relates to inductor current by: IIND(PK) = 1.25 IOUT Thus, for a 250mA output load step with VIN = 3.35V and VOUT = 1.5V: RC = (1.25 x 0.6 x 0.25)/6.75A = 27.8k Choose 27k. Note that the inductor does not limit the response in this case since it can ramp at (V IN VOUT)/4.7H, or (3.35 - 1.5)/4.7H = 394mA/s. The output filter capacitor is then chosen so that the COUT RLOAD pole cancels the RC CC zero: COUTRLOAD = RCCC For example: COUT = 27k x 3.3nF/4.3 = 20.7F Choose 22F. If the output filter capacitor has significant ESR, a zero occurs at: ZESR = 1/(2 COUTRESR) If ZESR > fC, it can be ignored, as is typically the case with ceramic output capacitors. If ZESR is less than fC, it should be cancelled with a pole set by capacitor CP connected from COMPSD to GND: CP = COUTRESR/RC If CP is calculated to be < 10pF, it can be omitted.
MAX1565
Auxiliary Controller Component Selection
External MOSFET All MAX1565 auxiliary controllers drive external logiclevel N-channel MOSFETs. Significant MOSFET selection parameters are: 1) On-resistance (RDS(ON)) 2) Maximum drain-to-source voltage (VDS(MAX)) 3) Total gate charge (QG) 4) Reverse transfer capacitance (CRSS) DL_ swings between OUTSU and GND. Use a MOSFET with on-resistance specified at or below the main output voltage. The gate charge, QG, includes all capacitance associated with charging the gate and helps to predict MOSFET transition time between on and off states. MOSFET power dissipation is a combination of on-resistance and transition losses. The on-resistance loss is: PRDSON = D IL2 RDS(ON) where D is the duty cycle, IL is the average inductor current, and RDS(ON) is MOSFET on-resistance. The transition loss is approximately: PTRANS = (VOUT IL fOSC tT)/3 where VOUT is the output voltage, IL is the average inductor current, fOSC is the switching frequency, and tT is the transition time. The transition time is approximately QG/IG, where QG is the total gate charge, and IG is the gate drive current (typically 0.5A). The total power dissipation in the MOSFET is: PMOSFET = PRDSON + PTRANS Diode For most auxiliary applications, a Schottky diode rectifies the output voltage. The Schottky diode's low forward voltage and fast recovery time provide the best performance in most applications. Silicon signal diodes (such as 1N4148) are sometimes adequate in low-current (<10mA) high-voltage (>10V) output circuits where the output voltage is large compared to the diode forward voltage. Auxiliary Compensation The auxiliary controllers employ voltage-mode control to regulate their output voltage. Optimum compensation somewhat depends on whether the design uses continuous or discontinuous inductor current.
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Discontinuous Inductor Current When the inductor current falls to zero on each switching cycle, it is described as discontinuous. The inductor is not utilized as efficiently as with continuous current. This often has little negative impact in light-load applications since the coil losses may already be low compared to other losses. A benefit of discontinuous inductor current is more flexible loop compensation and no maximum duty-cycle restriction on boost ratio. To ensure discontinuous operation, the inductor must have a sufficiently low inductance to fully discharge on each cycle. This occurs when: L < [VIN2 (VOUT - VIN)/VOUT3] [RLOAD/(2 fOSC)] A discontinuous current boost has a single pole at: fP = (2VOUT - VIN)/(2 RLOADCOUTVOUT) Choose the integrator capacitor such that the unity-gain crossover (fC) occurs at fOSC/10 or lower. Note that for many auxiliary circuits, such as those powering motors, LEDs, or other loads that do not require fast transient response, it is often acceptable to overcompensate by setting fC at fOSC/20 or lower. CC is then determined by: CC = [2VOUTVIN /((2VOUT - VIN)VRAMP)] [VOUT /(K(VOUT - VIN))]1/2 [(VFB/VOUT) (gM /(2 fC))] where K = 2 L fOSC/RLOAD, and VRAMP is the internal slope compensation voltage ramp of 1.25V. The CCRC zero is then used to cancel the fP pole, so: RC = RLOADCOUTVOUT/[(2VOUT - VIN) CC] Continuous Inductor Current Continuous inductor current can sometimes improve boost efficiency by lowering the ratio between peak inductor current and output current. It does this at the expense of a larger inductance value that requires larger size for a given current rating. With continuous inductor current boost operation, there is a right-plane zero at: fRHPZ = (1 - D)2 RLOAD /(2L) where (1 - D) = VIN/VOUT (in a boost converter). A complex pole pair is located at: f0 = VOUT/[2 VIN (L COUT)1/2] If the zero due to the output capacitor capacitance and ESR is less than 1/10 the right-plane zero: ZCOUT = 1/(2 COUT RESR) < fRHPZ/10 Choose C C such that the crossover frequency f C occurs at ZCOUT. The ESR zero provides a phase boost at crossover. CC = (VIN/VRAMP)(VFB/VOUT)(gM /(2 ZCOUT)) Choose RC to place the integrator zero, 1/(2 RCCC), at f0 to cancel one of the pole pairs: RC = VIN (L COUT)1/2/(VOUT CC) If ZCOUT is not less than fRHPZ/10 (as is typical with ceramic output capacitors) and continuous conduction is required, then cross the loop over before fRHPZ and f0: fC < f0/10, and fC < fRHPZ/10 In that case: CC = (VIN/VRAMP)(VFB/VOUT)(gM /(2 fC)) Place 1/(2 RCCC) = 1/(2 RLOADCOUT), so that RC = RLOAD COUT/CC or reduce the inductor value for discontinuous operation.
MAX1565
Applications Information
LED, LCD, and Other Boost Applications
Any auxiliary channel can be used for a wide variety of step-up applications. These include generating 5V or some other voltage for motor or actuator drive, generating 15V or a similar voltage for LCD bias, or generating a step-up current source to efficiently drive a series array of white LEDs for display backlighting. Figures 5 and 6 show examples of these applications.
TO VBATT 4.7F 4.7H 15V 100mA 22F 1.1M FB_ AUX_ PWM OUTSU DL_
100k
MAX1565 (PARTIAL)
Figure 5. Using an AUX_ Controller Channel to Generate LCD Bias
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21
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
TO VBATT 1F 10H OUTSU 1F DL_ IN WHITE LEDs FB_ AUX_ PWM DCON DL PART OF MAX1565 FB C2 Q1 R1 INPUT 1-CELL Li+ MAIN L1 L2 D1
OUTPUT 3.3V
62 (FOR 20mA)
MAX1565 (PARTIAL)
R2
Figure 6. AUX_ Channel Powering a White LED Step-Up Current Source
Figure 7. Auxiliary SEPIC Configuration
SEPIC Buck-Boost
The MAX1565's internal switch step-up and step-down can be cascaded to make a high-efficiency buck-boost converter, but it may sometimes be desirable to build a second buck-boost converter with an AUX_ controller. One type of step-up/step-down converter is the SEPIC (Figure 7). Inductors L1 and L2 can be separate inductors or wound on a single core and coupled like a transformer. Typically, a coupled inductor improves efficiency since some power is transferred through the coupling, causing less power to pass through the coupling capacitor (C2). Likewise, C2 should have low ESR to improve efficiency. The ripple current rating must be greater than the larger of the input and output currents. The MOSFET (Q1) drain-to-source voltage rating, and the rectifier (D1) reverse-voltage rating must exceed the sum of the input and output voltages. Other types of step-up/step-down circuits are a flyback converter and a step-up converter followed by a linear regulator.
secondary that is not fed back is small when compared to the load on the one that is. Regulation also improves if the load current range is limited. Consult the transformer manufacturer for the proper design for a given application.
Boost with Charge Pump for Positive and Negative Outputs
Negative output voltages can be produced without a transformer, using a charge-pump circuit with an auxiliary controller as shown in Figure 9. When MOSFET Q1 turns off, the voltage at its drain rises to supply current to VOUT+. At the same time, C1 charges to the voltage VOUT+ through D1.
TO VBATT 1F 1F +15V 30mA CCD+ 1.1M
Multiple Output Flyback Circuits
Some applications require multiple voltages from a single converter channel. This is often the case when generating voltages for CCD bias or LCD power. Figure 8 shows a two-output flyback configuration with AUX_. The controller drives an external MOSFET that switches the transformer primary. Two transformer secondaries generate the output voltages. Only one positive output voltage can be fed back, so the other voltages are set by the turns ratio of the transformer secondaries. The load stability of the other secondary voltages depends on transformer leakage inductance and winding resistance. Voltage regulation is best when the load on the
22
AUX_ PWM 1F OUTSU DL_
100k
-7.5V 20mA CCD*(SEE NOTE)
FB_
MAX1565 (PARTIAL)
*LOAD RESISTOR REQUIRED IF -7.5V OPERATES WITH NO LOAD
Figure 8. +15V and -7.5V CCD Bias with Transformer
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
L1 10H TO VBATT 1F
D2 C2 1F
VOUT+ +15V 20mA R1 1M
AUX_ PWM OUTSU
FB_ R2 90.9k D3 C3 1F VOUT-15V 10mA
Q1 DL_
C1 1F D1
When the MOSFET turns on, C1 discharges through D3, thereby charging C3 to V OUT - minus the drop across D3 to create roughly the same voltage as VOUT+ at VOUT- but with inverted polarity. If different magnitudes are required for the positive and negative voltages, a linear regulator can be used at one of the outputs to achieve the desired voltages. One such connection is shown in Figure 10. This circuit is somewhat unique in that a positive output linear regulator is able to regulate the negative output. It does this by controlling the charge to the flying capacitor rather than directly regulating at the output.
MAX1565
Adding a MAX1801 Slave
The MAX1801 is a 6-pin SOT slave DC-to-DC controller that can be connected to generate additional output voltages. It does not generate its own reference or oscillator. Instead, it uses the reference and oscillator of the MAX1565 (Figure 11). The MAX1801 controller operation and design are similar to that of a MAX1565 AUX controller. All comments in the Auxiliary Controller Component Selection section also apply to add-on MAX1801 slave controllers. For more details, refer to the MAX1801 data sheet.
MAX1565 (PARTIAL)
Figure 9. 15V Output Using a Boost with Charge-Pump Inversion
10H TO VBATT 1F 1F 1M AUX_ PWM OUTSU Q1 DL_ 1F FB_ 90.9k
+15V 20mA
-7.5V 20mA 1F 110k 1F 549k
MAX1565 (PARTIAL)
IN SHDN GND
OUT
FB_ +1.25V
MAX1616 Figure 10. +15V and -7.5V CCD Bias without Transformer ______________________________________________________________________________________ 23
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
TO BATT
VOUT DL IN
OUTSU
MAX1801 OSC
FB COMP GND REF DCON
OSC
MAX1565 (PARTIAL)
REF
Figure 11. Connecting the MAX1801 Slave PWM Controller to the MAX1565
Using SDOK for Power Sequencing
SDOK goes low when the step-down reaches regulation. Some microcontrollers with low-voltage cores require that the high-voltage (3.3V) I/O rail not be powered up until the core has a valid supply. The circuit in Figure 12 accomplishes this by driving the gate of a PFET connected between the 3.3V output and the microcontroller I/O supply. Alternately, power sequencing may be implemented by connecting RC networks to the appropriate converter ON_ inputs.
MAX1565 (PARTIAL)
OUTSUB OUTSUA TO VBATT
3.35V
STEP-UP
LXSU
10H
Setting OUTSD Below 1.25V
The step-down feedback voltage is 1.25V when FBSELSD is high. With a standard two-resistor feedback network, the output voltage may be set to values between 1.25V and the input voltage. If a step-down output voltage less than 1.25V is desired, it can be set by adding a third feedback resistor from FB to a voltage higher than 1.25V (the step-up output is a convenient voltage for this) as shown in Figure 13. The equation governing output voltage shown in Figure 13 is: 0 = [(VSD - VFBSD)/R1] + [(0 - VFBSD)/R2] + [(VSU - VFBSD)/R3] where VSD is the output voltage, VFBSD is 1.25V, and VSU is the step-up output voltage. Note that any available voltage that is higher than 1.25V can be used as the connection point for R3 in Figure 13 and for the VSD term in the equation. Since there are multiple solutions for R1, R2, and R3, the above equation cannot be written in terms of one resistor. The best method for determining resistor values is to enter the above equation into a spreadsheet and test estimated resistors' values. A good starting point is with 100k at R2 and R3.
24
STEP-DOWN PGNDB
10F
3.3V TO CPU 1M
FBSU SDOK
1M
INSD 10F
TO VBATT OR OUTSU
LXSD
4.7H
VCORE 1.5V 10F
FBSD PGNDA
Figure 12. Using SDOK to Gate 3.3V Power to CPU After the Core Voltage is OK
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Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply
Designing a PC Board
Good PC board layout is important to achieve optimal performance from the MAX1565. Poor design can cause excessive conducted and/or radiated noise. Conductors carrying discontinuous currents, and any high-current path should be made as short and wide as possible. A separate low-noise ground plane containing the reference and signal grounds should connect to the power-ground plane at only one point to minimize the effects of power-ground currents. Typically, the ground planes are best joined right at the IC. Keep the voltage feedback network very close to the IC, preferably within 0.2in (5mm) of the FB_ pin. Nodes with high dV/dt (switching nodes) should be kept as small as possible and should be routed away from high-impedance nodes such as FB_. Refer to the MAX1565EVKIT evaluation kit data sheet for a full PC board example.
VSU 3.3V OUTSUA OUTSUB FBSELSD
MAX1565
MAX1565 (PARTIAL)
INSD 10F
CURRENT-MODE STEP-DOWN
LXSD
4.7H 22F
VSD 0.8V
PGNDA FBSD R3 100k VFBSD 1.25V R1 56k
R2 100k
Figure 13. Setting OUTSD for Outputs Below 1.25V
Chip Information
TRANSISTOR COUNT: 9420 PROCESS: BiCMOS
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25
Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply MAX1565
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
QFN THIN.EPS
L
REV.
0.15 C A
D2
C L
D
b D2/2
0.10 M C A B
PIN # 1 I.D.
D/2
0.15 C B
k
PIN # 1 I.D. 0.35x45
E/2 E2/2 E (NE-1) X e
C L
E2
k L
DETAIL A
e (ND-1) X e
C L
C L
L
e 0.10 C A 0.08 C
e
C
A1 A3
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO.
21-0140
C
1 2
COMMON DIMENSIONS
EXPOSED PAD VARIATIONS
NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm.
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO. REV.
21-0140
C
2 2
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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