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19-3872; Rev 0; 3/06
KIT ATION EVALU BLE AVAILA
2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
General Description Features
Wide Input Voltage Range: 6.5V to 76V Fixed (3.3V, 5V) and Adjustable (1.265V to 11V) Output-Voltage Versions 2A Output Current Efficiency Up to 92% Internal 0.26 High-Side DMOS FET 310A Quiescent Current at No Load 19A Shutdown Current Internal Frequency Compensation Fixed 127kHz Switching Frequency External Frequency Synchronization Thermal Shutdown and Short-Circuit Current Limit
MAX5090A/B/C
The MAX5090A/B/C easy-to-use, high-efficiency, highvoltage step-down DC-DC converters operate from an input voltage up to 76V, and consume only 310A quiescent current at no load. This pulse-width-modulated (PWM) converter operates at a fixed 127kHz switching frequency at heavy loads, and automatically switches to pulse-skipping mode to provide low quiescent current and high efficiency at light loads. The MAX5090 includes internal frequency compensation simplifying circuit implementation. The device can also be synchronized with external system clock frequency in a noise-sensitive application. The MAX5090 uses an internal low on-resistance and a high-voltage DMOS transistor to obtain high efficiency and reduce overall system cost. This device includes undervoltage lockout, cycle-by-cycle current limit, hiccup-mode output short-circuit protection, and overtemperature shutdown. The MAX5090 delivers up to 2A output current. External shutdown is included, featuring 19A (typ) shutdown current. The MAX5090A/MAX5090B versions have fixed output voltages of 3.3V and 5V, respectively, while the MAX5090C features an adjustable 1.265V to 11V output voltage. The MAX5090 is available in a space-saving 16-pin thin QFN package (5mm x 5mm) and operates over the automotive temperature range (-40C to +125C).
-40C to +125C Automotive Temperature Range 16-Pin (5mm x 5mm) Thin QFN Package Capable of Dissipating 2.67W at +70C
Ordering Information
PART TEMP RANGE PINPACKAGE* OUTPUT VOLTAGE (V) 3.3 3.3 5.0 5.0
MAX5090AATE+ -40C to +125C 16 TQFN-EP** MAX5090AATE -40C to +125C 16 TQFN-EP**
Applications
Automotive Industrial Distributed Power
MAX5090BATE+ -40C to +125C 16 TQFN-EP** MAX5090BATE -40C to +125C 16 TQFN-EP**
Ordering Information continued at end of data sheet. *The package code is T1655-3. **EP = Exposed pad. +Denotes lead-free package.
Typical Operating Circuit
PGND N.C.
Pin Configuration
SGND 10
TOP VIEW
VIN 7.5V TO 76V RIN 10 CBYPASS 0.47F VIN ON/OFF BST FB SYNC SGND PGND SS VD 3.3F CSS 0.047F DRAIN LX CBST 0.22F D1 PDS5100H COUT 100F 100H VOUT 5V/2A
12
11
ON/OFF 9
CIN 68F
DRAIN 13 DRAIN 14 N.C. 15 N.C. 16
EP
8 7
FB SS SYNC VD
MA5090
6 5
MAX5090B
1 LX
2 LX
3 BST
4 VIN
TQFN
________________________________________________________________ Maxim Integrated Products
1
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
ABSOLUTE MAXIMUM RATINGS
(Voltages referenced to PGND, unless otherwise specified.) VIN, DRAIN .............................................................-0.3V to +80V SGND, PGND..............................................-0.3V to +0.3V LX.................................................................-0.8V to (VIN + 0.3V) BST ...............................................................-0.3V to (VIN + 10V) BST to LX................................................................-0.3V to +10V ON/OFF........................................................-0.3V to (VIN + 0.3V) VD, SYNC ...............................................................-0.3V to +12V SS..................................................................-0.3 to +4V FB MAX5090A/MAX5090B......................... .......-0.3V to +15V MAX5090C ................1mA (internally clamped to +2V, -0.3V) *As per JEDEC 51 Standard Multilayer Board.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause 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.
VOUT Short-Circuit Duration.............................. ...Continuous VD Short-Circuit Duration.........................................Continuous Continuous Power Dissipation (TA = +70C)* 16-Pin TQFN (derate 33.3mW/C above +70C) ........2.667W Operating Junction Temperature Range ...........-40C to +125C Storage Temperature Range ............................-65C to +150C Junction Temperature..............................................+150C Lead Temperature (soldering, 10s) .................................+300C
ELECTRICAL CHARACTERISTICS
(VIN = +12V, VON/OFF = +12V, VSYNC = 0V, IOUT = 0, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Operating Circuit.) (Note 1)
PARAMETER Input Voltage Range Undervoltage Lockout UVLO Hysteresis Output Voltage Output Voltage Range Feedback Voltage Efficiency SYMBOL VIN UVLO UVLOHYS MAX5090A VOUT VOUT VFB MAX5090B MAX5090B VIN = 6.5V to 76V, IOUT = 0 to 2A VIN = 7.5V to 76V, IOUT = 0 to 2A VIN = 7V to 76V, IOUT = 0 to 1A 3.20 4.85 4.85 1.265 1.191 1.228 80 88 88 310 310 310 310 310 310 310 310 310 19 550 550 550 570 570 570 650 650 650 45 A A A A % VIN rising CONDITIONS MIN 6.5 5.70 6.17 0.5 3.3 5.0 5.0 3.39 5.15 5.15 11.000 1.265 V V V TYP MAX 76.0 6.45 UNITS V V V
MAX5090C only MAX5090C, VIN = 6.5V to 76V MAX5090A MAX5090B MAX5090C MAX5090A VIN = 12V, IOUT = 1A VIN = 12V, IOUT = 1A VIN = 12V, VOUT = 5V, IOUT = 1A VIN = 6.5V to 28V VIN = 7V to 28V VIN = 6.5V to 28V VIN = 6.5V to 40V VIN = 7V to 40V VIN = 6.5V to 40V VIN = 6.5V to 76V VIN = 7V to 76V VIN = 6.5V to 76V
Quiescent Supply Current (Note 2)
IQ
MAX5090B MAX5090C MAX5090A
Quiescent Supply Current (Note 2)
IQ
MAX5090B MAX5090C MAX5090A
Quiescent Supply Current (Note 2) Shutdown Current SOFT-START Default Internal Soft-Start Period Soft-Start Charge Current
IQ ISHDN
MAX5090B MAX5090C
VON/OFF = 0V, VIN = 14V
CSS = 0 ISS 4.5
700 10 16.0
s A
2
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V, VON/OFF = +12V, VSYNC = 0V, IOUT = 0, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Operating Circuit.) (Note 1)
PARAMETER Soft-Start Reference Voltage Peak Switch Current Limit Switch Leakage Current Switch On-Resistance PFM Threshold PFM Threshold FB Input Bias Current ON/OFF CONTROL INPUT ON/OFF Input-Voltage Threshold ON/OFF Input-Voltage Hysteresis ON/OFF Input Current Oscillator Frequency Synchronization Maximum Duty Cycle SYNC High-Level Voltage SYNC Low-Level Voltage SYNC Minimum Pulse Width SYNC Input Leakage INTERNAL VOLTAGE REGULATOR Regulator Output Voltage Dropout Voltage Load Regulation VD/IVD VD VIN = 9V to 76V, IOUT = 0 6.5V VIN 8.5V, IOUT = 15mA 0 to 15mA 7.0 7.8 0.5 10 8.4 V V -1 VON/OFF VHYST ION/OFF f0SC fSYNC DMAX VIN = 6.5V to 76V, VOUT 11V VON/OFF = 0V to VIN 106 119 80 2.0 0.8 350 +1 95 Rising trip point 1.180 1.38 100 10 127 100 150 200 1.546 V mV nA kHz kHz % V V ns A SYMBOL VSS(REF) ILIM IOL RDS(ON) IPFM IPFM IB (Note 3) VIN = 76V, VON/OFF = 0V, VLX = 0V ISWITCH = 1A Minimum switch current in any cycle Minimum switch current in any cycle at TJ +25C (Note 4) MAX5090C, VFB = 1.2V 1 14 -150 +0.1 CONDITIONS MIN 1.23 2.4 -10 0.26 60 TYP 1.46 3.3 MAX 1.65 5.0 +10 0.4 300 300 +150 UNITS V A A mA mA nA
MAX5090A/B/C
INTERNAL SWITCH/CURRENT LIMIT
OSCILLATOR/SYNCHRONIZATION
PACKAGE THERMAL CHARACTERISTICS Thermal Resistance (Junction to Ambient) THERMAL SHUTDOWN Thermal-Shutdown Junction Temperature Thermal-Shutdown Hysteresis TSH THYST Temperature rising +175 20 C C JA TQFN package (JEDEC 51) 30 C/W
Note 1: All limits at -40C are guaranteed by design, not production tested. Note 2: For total current consumption during switching (at no load), also see the Typical Operating Characteristics. Note 3: Switch current at which the current-limit circuit is activated. Note 4: Limits are guaranteed by design.
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
Typical Operating Characteristics
(VIN = 12V, VON/OFF =12V, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Operating Circuit, if applicable.)
VOUT vs. TEMPERATURE (MAX5090AATE, VOUT = 3.3V)
MAX5090 toc01
VOUT vs. TEMPERATURE (MAX5090BATE, VOUT = 5V)
MAX5090 toc02
LINE REGULATION (MAX5090AATE, VOUT = 3.3V)
3.38 3.36 3.34 IOUT = 0
MAX5090 toc03
3.40 3.38 3.36 3.34 VOUT (V)
5.15 5.10 5.05 VOUT (V)
3.40
3.30 3.28 3.26 3.24 3.22 3.20 -50 -25 0 25 50 75 100 125 150 AMBIENT TEMPERATURE (C) IOUT = 2A
5.00 4.95 4.90 4.85 -50 -25 0 25 50 75 100 125 150 AMBIENT TEMPERATURE (C) IOUT = 2A
VOUT (V)
3.32
IOUT = 0
IOUT = 0
3.32 3.30 3.28 3.26 3.24 3.22 3.20 6.5 16 26
IOUT = 2A
36
46
56
66
76
VIN (V)
LINE REGULATION (MAX5090BATE, VOUT = 5V)
MAX5090 toc04
LOAD REGULATION (MAX5090AATE, VOUT = 3.3V)
MAX5090 toc05
LOAD REGULATION (MAX5090BATE, VOUT = 5V)
MAX5090 toc06
5.15 5.10 5.05 VOUT (V) 5.00 4.95 4.90 4.85 6.5 16 26 36 46 56 66 IOUT = 0
3.40 3.38 3.36 3.34 VOUT (V) VIN = 76V
5.15 5.10 5.05 VOUT (V) 5.00 4.95 4.90 4.85 VIN = 6.5V VIN = 24V VIN = 76V
3.32 3.30 3.28
IOUT = 2A
3.26 3.24 3.22 3.20 76 0.1
VIN = 6.5V
VIN = 24V
1
10
100 ILOAD (mA)
1000
10,000
0.1
1
10
100 ILOAD (mA)
1000
10,000
VIN (V)
EFFICIENCY vs. LOAD CURRENT (MAX5090AATE, VOUT = 3.3V)
MAX5090 toc07
EFFICIENCY vs. LOAD CURRENT (MAX5090BATE, VOUT = 5V)
MAX5090 toc08
OUTPUT CURRENT LIMIT vs. TEMPERATURE (MAX5090AATE)
VOUT = 3.3V 5% DROP IN VOUT PULSED OUTPUT LOAD
MAX5090 toc09
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 400 800 1200 1600 VIN = 6.5V VIN = 12V VIN = 24V VIN = 48V VIN = 76V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VIN = 76V VIN = 6.5V VIN = 12V VIN = 24V VIN = 48V
4.0 3.5 3.0 2.5 2.0 1.5 1.0
OUTPUT CURRENT LIMIT (A)
2000
0
400
800
1200
1600
2000
-50
-25
0
25
50
75
100 125 150
LOAD CURRENT (mA)
LOAD CURRENT (mA)
AMBIENT TEMPERATURE (C)
4
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF =12V, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Operating Circuit, if applicable.)
OUTPUT CURRENT LIMIT vs. TEMPERATURE (MAX5090BATE)
MAX5090 toc010
OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE (MAX5090AATE)
VOUT = 3.3V 5% DROP IN VOUT PULSED OUTPUT LOAD
MAX5090 toc11
OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE (MAX5090BATE)
VOUT = 5V 5% DROP IN VOUT PULSED OUTPUT LOAD
MAX5090 toc12
4.0 3.5 3.0 2.5 2.0 1.5 1.0
OUTPUT CURRENT LIMIT (A)
OUTPUT CURRENT LIMIT (A)
OUTPUT CURRENT LIMIT (A)
VOUT = 5V 5% DROP IN VOUT PULSED OUTPUT LOAD
7.0 6.0 5.0 4.0 3.0 2.0 1.0
7.0 6.0 5.0 4.0 3.0 2.0 1.0
-50
-25
0
25
50
75
100 125 150
6.5
16
26
36
46
56
66
76
6.5
16
26
36
46
56
66
76
AMBIENT TEMPERATURE (C)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE (MAX5090AATE)
MAX5090 toc13
NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE (MAX5090AATE)
MAX5090 toc14
SHUTDOWN CURRENT vs. TEMPERATURE (MAX5090AATE)
VOUT = 3.3V SHUTDOWN CURRENT (A) 26
MAX5090 toc15
600 VOUT = 3.3V NO-LOAD SUPPLY CURRENT (A) 550 500 450 400 350 300 -50 -25 0 25 50 75
600 VOUT = 3.3V NO-LOAD SUPPLY CURRENT 550 500 450 400 350 300
30
22
18
14
10 6.5 16 26 36 46 56 66 76 -50 -25 0 25 50 100 125 150 175 INPUT VOLTAGE (V) AMBIENT TEMPERATURE (C)
100 125 150
AMBIENT TEMPERATURE (C)
SHUTDOWN CURRENT vs. INPUT VOLTAGE
MAX5090 toc16
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX5090 toc17
LOAD-TRANSIENT RESPONSE (MAX5090AATE)
MAX5090 toc18
45 40 SHUTDOWN CURRENT (A) 35 30 25 20 15 10 5 0 6.5 16 26 36 46 56 66 76 INPUT VOLTAGE (V) VOUT = 3.3V
13 MAX5090CATE VOUT = 11V VON/OFF = VIN
VOUT = 3.3V A
11
VOUT (V)
9 IOUT = 2A 6 IOUT = 1A IOUT = 0A B
3
0 5 6 7 8 9 10 11 11.5 12 12.5 13 VIN (V) 400s/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 1A/div, 1A TO 2A
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF =12V, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Operating Circuit, if applicable.)
LOAD-TRANSIENT RESPONSE (MAX5090AATE)
MAX5090 toc19
LX WAVEFORMS (MAX5090AATE)
MAX5090 toc20
LX WAVEFORMS (MAX5090AATE)
MAX5090 toc21
VOUT = 3.3V A A VOUT = 3.3V VOUT = 3.3V A
B
B 0
B
400s/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 500mA/div, 0.1A TO 1A
4s/div A: SWITCH VOLTAGE (LX PIN), 20mV/div (VIN = 48V) B: INDUCTOR CURRENT, 2A/div (I0 = 2A)
4s/div A: SWITCH VOLTAGE, 20V/div (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (I0 = 75mA)
LX WAVEFORM (MAX5090AATE)
MAX5090 toc22
STARTUP WAVEFORM (IOUT = 0)
MAX5090 toc23
STARTUP WAVEFORM (IOUT = 2A)
MAX5090 toc24
VOUT = 3.3V A A A
B B CSS = 0.047F 4s/div A: SWITCH VOLTAGE, 20V/div (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (IOUT = 0) A: VON/OFF, 2V/div B: VOUT, 1V/div 4ms/div A: VON/OFF, 2V/div B: VOUT, 1V/div 4ms/div CSS = 0.047F
B
PEAK SWITCH CURRENT vs. INPUT VOLTAGE
MAX5090 toc25
SYNCHRONIZATION
MAX5090 toc26
SYNCHRONIZATION
MAX5090 toc27
7.0 6.0 5.0 4.0 3.0 2.0 1.0 6.5 16 26 36 46 56 66 MAX5090AATE VOUT = 3.3V 5% DROP IN VOUT PULSED OUTPUT LOAD
fSYNC = 119kHz SYNC 2V/div
fSYNC = 200kHz SYNC 2V/div
PEAK SWITCH CURRENT (A)
LX 10V/div
LX 10V/div
76
2s/div
1s/div
INPUT VOLTAGE (V)
6
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
Pin Description
PIN 1, 2 3 4 5 6 7 NAME LX BST VIN VD SYNC SS FUNCTION Source Connection of Internal High-Side Switch Boost Capacitor Connection. Connect a 0.22F ceramic capacitor from BST to LX. Input Voltage. Bypass VIN to SGND with a low-ESR capacitor as close to the device as possible. Internal Regulator Output. Bypass VD to PGND with a 3.3F/10V or greater ceramic capacitor. Synchronization Input. Connect SYNC to an external clock for synchronization. Connect to SGND to select the internal 127kHz switching frequency. Soft-Start Capacitor Connection. Connect an external capacitor from SS to SGND to adjust the softstart time. Output Sense Feedback Connection. For fixed output voltage (MAX5090A/MAX5090B), connect FB to VOUT. For adjustable output voltage (MAX5090C), use an external resistive voltage-divider to set VOUT. VFB regulating set point is 1.228V. Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for normal operation. Connect ON/OFF to VIN with short leads for always-on operation. Signal Ground. SGND must be connected to PGND for proper operation. No Connection. Not internally connected. Power Ground Internal High-Side Switch Drain Connection Exposed Pad. Solder EP to SGND plane to aid in heat dissipation. Do not use as the only electrical ground connection.
MAX5090A/B/C
8
FB
9 10 11, 15, 16 12 13, 14 --
ON/OFF SGND N.C. PGND DRAIN EP
Detailed Description
The MAX5090 step-down DC-DC converter operates from a 6.5V to 76V input voltage range. A unique voltage-mode control scheme with voltage feed-forward and an internal switching DMOS FET provides high efficiency over a wide input voltage range. This pulsewidth-modulated converter operates at a fixed 127kHz switching frequency or can be synchronized with an external system clock frequency. The device also features automatic pulse-skipping mode to provide high efficiency at light loads. Under no load, the MAX5090 consumes only 310A, and in shutdown mode, consumes only 20A. The MAX5090 also features undervoltage-lockout, hiccup-mode output short-circuit protection and thermal shutdown.
R1 VUVLO(TH) = 1 + x 1.38 R2 Set the external VUVLO(TH) to greater than 6.45V. The maximum recommended value for R2 is less than 1M. ON/OFF is a logic input and can be safely driven to the full VIN range. Connect ON/OFF to VIN for automatic startup. Drive ON/OFF to ground to shut down the MAX5090. Shutdown forces the internal power MOSFET off, turns off all internal circuitry, and reduces the V IN supply current to 20A (typ). The ON/OFF rising threshold is 1.546V (max). Before any operation begins, the voltage at ON/OFF must exceed 1.546V. The ON/OFF input has 100mV hysteresis. If the external UVLO threshold setting divider is not used, an internal undervoltage-lockout feature monitors the supply voltage at VIN and allows the operation to start when VIN rises above 6.45V (max). The internal UVLO rising threshold is set at 6.17V with 0.5V hysteresis. The VIN and VON/OFF voltages must be above 6.5V and 1.546V, respectively, for proper operation.
7
ON/OFF/Undervoltage Lockout (UVLO)
Use the ON/OFF function to program the external UVLO threshold at the input. Connect a resistive voltagedivider from V IN to SGND with the center node to ON/OFF, as shown in Figure 1. Calculate the threshold value by using the following formula:
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
Simplified Functional Diagram
ON/OFF VIN DRAIN
ENABLE 1.38V
REGULATOR (FOR ANALOG)
CPFM
IREF-PFM HIGH-SIDE CURRENT SENSE
VD
REGULATOR (FOR DRIVER)
VREF
OSC
RAMP
CILIM IREF-LIM
CLKI SRMP SYNC SRAMP SCK MUX
RMP BST
SS MIN FB *RH x1 *RL TYPE 3 COMPENSATION EAMP RAMP
CLK N CONTROL LOGIC LX CPWM
THERMAL SHUTDOWN PGND
MAX5090
*RH = 0 AND RL = FOR MAX5090C
SGND
8
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
Boost High-Side Gate Drive (BST)
Connect a flying bootstrap capacitor between LX and BST to provide the gate-drive voltage to the high-side n-channel DMOS switch. The capacitor is alternately charged from the internally regulated output-voltage VD and placed across the high-side DMOS driver. Use a 0.22F, 16V ceramic capacitor located as close to the device as possible. On startup, an internal low-side switch connects LX to ground and charges the BST capacitor to (VD - VDIODE). Once the BST capacitor is charged, the internal low-side switch is turned off and the BST capacitor voltage provides the necessary enhancement voltage to turn on the high-side switch.
Soft-Start (SS)
The MAX5090 provides the flexibility to externally program a suitable soft-start time for a given application. Connect an external capacitor from SS to SGND to use the external soft-start. Soft-start gradually ramps up the reference voltage seen by the error amplifier to control the output's rate of rise and reduce the input surge current during startup. For soft-start time longer than 700s, use the following equation to calculate the soft-start capacitor (CSS) required for the soft-start time (tSS): CSS = 10 x 10 -6 x t SS 1.46
MAX5090A/B/C
Synchronization (SYNC)
SYNC controls the oscillator frequency. Connect SYNC to SGND to select 127kHz operation. Use the SYNC input to synchronize to an external clock. SYNC has a guaranteed frequency range of 119kHz to 200kHz when using an external clock. When SYNC is connected to SGND, the internal clock is used to generate a ramp with the amplitude in proportion to V IN and the period corresponding to the internal clock frequency to modulate the duty cycle of the high-side switch. If an external clock (SYNC clock) is applied at SYNC for four cycles, the MAX5090 selects the SYNC clock. The MAX5090 generates a ramp (SYNC ramp) with the amplitude in proportion to VIN and the period corresponding to the SYNC clock frequency. The MAX5090 initially blanks the SYNC ramp for 375s (typ) to allow the ramp to reach its target amplitude (proportion to the VIN supply). After the SYNC blanking time, the SYNC ramp and the SYNC clock switch to the PWM controller and replace the internal ramp and the internal clock, respectively. If the SYNC clock is removed for three internal clock cycles, the internal clock and the internal ramp switch back to the PWM controller. The minimum pulse-width requirement for the external clock is 350ns, and if the requirement is not met, the MAX5090 could ignore the clock as a noisy bounce.
where tSS > 700s and CSS is in Farads. The MAX5090 also provides an internal soft-start (700s, typ) with a current source to charge an internal capacitor to rise up to the bandgap reference voltage. The internal soft-start voltage will eventually be pulled up to 3.4V. The internal soft-start reference also feeds to the error amplifier. The error amplifier takes the lowest voltage among SS, the internal soft-start voltage, and the bandgap reference voltage as the input reference for VOUT. Soft-start occurs when power is first applied and when the device exits shutdown. The MAX5090 also goes through soft-start when coming out of thermal-overload protection. During a soft-start, if the voltage at SS (VSS) is charged up to 1.46V in less than 700s, the MAX5090 takes its default internal soft-start (700s) to ramp up as its reference. After the SS and the internal soft-start ramp up over the bandgap reference, the error amplifier takes the bandgap reference.
Thermal-Overload Protection
The MAX5090 features integrated thermal-overload protection. Thermal-overload protection limits power dissipation in the device, and protects the device from a thermal overstress. When the die temperature exceeds +175C, an internal thermal sensor signals the shutdown logic, turning off the internal power MOSFET, resetting the internal soft-start and allowing the IC to cool. The thermal sensor turns the internal power MOSFET back on after the IC's die temperature cools down to +155C, resulting in a pulsed output under continuous thermal-overload conditions.
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
VIN 6.5V TO 76V RIN 10 CBYPASS 0.47F VIN ON/OFF R2 BST DRAIN LX 0.22F D1 PDS5100H COUT 100F 100H VOUT 3.3V, 2A
CIN 68F R1
MAX5090A
SYNC SGND PGND
FB SS VD 3.3F 0.047F
Figure 1. Fixed Output-Voltage Configuration
VIN 7.5V TO 76V RIN 10 CBYPASS 0.47F VIN ON/OFF DRAIN LX 0.22F BST D1 PDS5100H COUT 100F 100H VOUT 5.25V, 2A
CIN 68F
R3
MAX5090C
SYNC SGND PGND
FB SS 0.047F VD 3.3F R4
Figure 2. Adjustable Output-Voltage Configuration
10
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
Thermal-overload protection is intended to protect the MAX5090 in the event of a fault condition. For normal circuit operation, do not exceed the absolute maximum junction temperature rating of TJ = +150C.
MAX5090A/B/C
Table 1. Diode Selection
VIN (V) DIODE PART NUMBER B340LB 6.5 to 36 RB051L-40 MBRS340T3 MBRM560 6.5 to 56 RB095B-60 MBRD360T4 6.5 to 76 50SQ80 PDS5100H MANUFACTURER Diodes Inc. Central Semiconductor ON Semiconductor Diodes Inc. Central Semiconductor ON Semiconductor IR Diodes Inc.
Setting the Output Voltage
The MAX5090A/MAX5090B have preset output voltages of 3.3V and 5.0V, respectively. Connect FB to VOUT for the preset output voltage (Figure 1). The MAX5090C offers an adjustable output voltage. Set the output voltage with a resistive divider connected from the circuit's output to ground (Figure 2). Connect the center node of the divider to FB. Choose R4 less than 15k, then calculate R3 as follows: R3 = (VOUT - 1.228) x R4 1.228
The MAX5090 features internal compensation for optimum closed-loop bandwidth and phase margin. Because of the internal compensation, the output must be sensed immediately after the primary LC.
Inductor Selection
The MAX5090 is a fixed-frequency converter with fixed internal frequency compensation. The internal fixed compensation assumes a 100H inductor and 100F output capacitor with 50m ESR. It relies on the location of the double LC pole and the ESR zero frequency for proper closed-loop bandwidth and the phase margin at the closed-loop unity-gain frequency. See Table 2 for proper component values. Usually, the choice of an inductor is guided by the voltage difference between VIN and VOUT, the required output current and the operating frequency of the circuit. However, use the recommended inductors in Table 2 to ensure stable operation with optimum bandwidth. Use an inductor with a maximum saturation current rating greater than or equal to the maximum peak current limit (5A). Use inductors with low DC resistance for a higher efficiency converter.
rating greater than the highest expected output current. Use a rectifier with a voltage rating greater than the maximum expected input voltage, VIN. Use a low forward-voltage Schottky rectifier for proper operation and high efficiency. Avoid higher than necessary reversevoltage Schottky rectifiers that have higher forward-voltage drops. Use a Schottky rectifier with forward-voltage drop (V F) less than 0.55V and 0.45V at +25C and +125C, respectively, and at maximum load current to avoid forward biasing of the internal parasitic body diode (LX to ground). See Figure 3 for forward-voltage drop vs. temperature of the internal body diode of the MAX5090. Internal parasitic body-diode conduction may cause improper operation, excessive junction temperature rise, and thermal shutdown. Use Table 1 to choose the proper rectifier at different input voltages and output current.
Input Bypass Capacitor
The discontinuous input current waveform of the buck converter causes large ripple currents in the input capacitor. The switching frequency, peak inductor current, and the allowable peak-to-peak voltage ripple reflecting back to the source dictate the capacitance requirement. The MAX5090 high switching frequency allows the use of smaller value input capacitors. The input ripple is comprised of VQ (caused by the capacitor discharge) and VESR (caused by the ESR of the capacitor). Use low-ESR aluminum electrolytic capacitors with high-ripple current capability at the input. Assuming that the contribution from the ESR and capacitor discharge is equal to 90% and 10%, respectively, calculate the input capacitance and the ESR required for a specified ripple using the following equations:
Selecting a Rectifier
The MAX5090 requires an external Schottky rectifier as a freewheeling diode. Connect this rectifier close to the device using short leads and short PC board traces. The rectifier diode must fully conduct the inductor current when the power FET is off to have a full rectifier function. Choose a rectifier with a continuous current
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
ESRIN = VESR IL IOUT + 2
800 700 600 VF_D1 (mV) 500 400 300 200 100 0 -40 25 100 TEMPERATURE (C) 125 150
I x D(1 - D) CIN = OUT VQ x fSW where: IL = (VIN - VOUT ) x VOUT VIN x fSW x L V D = OUT VIN
IOUT is the maximum output current of the converter and fSW is the oscillator switching frequency (127kHz). For example, at VIN = 48V, VOUT = 3.3V, the ESR and input capacitance are calculated for the input peak-topeak ripple of 100mV or less, yielding an ESR and capacitance value of 40m and 100F, respectively. Low-ESR ceramic multilayer chip capacitors are recommended for size-optimized application. For ceramic capacitors assume the contribution from ESR and capacitor discharge is equal to 10% and 90%, respectively. The input capacitor must handle the RMS ripple current without significant rise in the temperature. The maximum capacitor RMS current occurs at approximately 50% duty cycle. Ensure that the ripple specification of the input capacitor exceeds the worst-case capacitor RMS ripple current. Use the following equations to calculate the input capacitor RMS current: ICRMS = IPRMS2 - IAVGin2 where:
IPRMS = IAVGin = D (IPK 2 + IDC 2 + IPK xIDC ) x 3 VOUT x IOUT
Figure 3. Forward-Voltage Drop vs. Temperature of the Internal Body Diode of MAX5090
Output Filter Capacitor
The output capacitor COUT forms double pole with the inductor and a zero with its ESR. The MAX5090's internal fixed compensation is designed for a 100F capacitor, and the ESR must be from 20m to 100m. The use of an aluminum or tantalum electrolytic capacitor is recommended. See Table 2 to choose an output capacitor for stable operation. The output ripple is comprised of VOQ (caused by the capacitor discharge), and VOESR (caused by the ESR of the capacitor). Use low-ESR tantalum or aluminum electrolytic capacitors at the output. Use the following equations to calculate the contribution of output capacitance and its ESR on the peak-to-peak output ripple voltage: VOESR = IL x ESR IL VOQ 8 xCOUT x fSW The MAX5090 has a programmable soft-start time (tSS). The output rise time is directly proportional to the output capacitor, output voltage, and the load. The output rise time also depends on the inductor value and the current-limit threshold. It is important to keep the output rise time at startup the same as the soft-start time (tSS) to avoid output overshoot. Large output capacitors take longer than the programmed soft-start time (tSS) and cause error-amplifier saturation. This results in output overshoot. Use greater than 2ms soft-start time for a 100F output capacitor.
VIN x IL IPK = IOUT + 2 IL IDC = IOUT - 2 VOUT D= VIN
IPRMS is the input switch RMS current, I AVGin is the input average current, and is the converter efficiency. The ESR of the aluminum electrolytic capacitor increases significantly at cold temperatures. Use a 1F or greater value ceramic capacitor in parallel with the aluminum electrolytic input capacitor, especially for input voltages below 8V.
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
In a dynamic load application, the allowable deviation of the output voltage during the fast transient load dictates the output capacitance value and the ESR. The output capacitors supply the step-load current until the controller responds with a greater duty cycle. The response time (tRESPONSE) depends on the closedloop bandwidth of the converter. The resistive drop across the capacitor ESR and capacitor discharge cause a voltage droop during a step-load. Use a combination of low-ESR tantalum and ceramic capacitors for better transient load and ripple/noise performance. Use the following equations to calculate the deviation of output voltage due to the ESR and capacitance value of the output capacitor: VOESR = ISTEP x ESROUT VOQ = ISTEP x tRESPONSE COUT 2) Minimize lead lengths to reduce stray capacitance, trace resistance, and radiated noise. In particular, place the Schottky rectifier diode right next to the device. Also, place the BST and VD bypass capacitors very close to the device. 3) Connect the exposed pad of the IC to the SGND plane. Do not make a direct connection between the exposed pad plane and SGND (pin 7) under the IC. Connect the exposed pad and pin 7 to the SGND plane separately. Connect the ground connection of the feedback resistive divider, ON/OFF threshold resistive divider, and the soft-start capacitor to the SGND plane. Connect the SGND plane and PGND plane at one point near the input bypass capacitor at VIN. 4) Use large SGND plane as a heatsink for the MAX5090. Use large PGND and LX planes as heatsinks for the rectifier diode and the inductor.
MAX5090A/B/C
where I STEP is the load step and t RESPONSE is the response time of the controller. Controller response time is approximately one-third of the reciprocal of the closed-loop unity-gain bandwidth, 20kHz typically.
Board Layout Guidelines
1) Minimize ground noise by connecting the anode of the Schottky rectifier, the input bypass capacitor ground lead, and the output filter capacitor ground lead to a large PGND plane.
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
Application Circuit
VIN RIN CIN R1 VIN ON/OFF R2 DRAIN LX CBST BST D1 COUT CBYPASS L1 VOUT
MAX5090B
SYNC SGND PGND
FB SS VD 3.3F CSS
Figure 4. Fixed Output Voltage
Table 2. Typical External Components Selection (Circuit of Figure 4)
VIN (V) VOUT (V) IOUT (A) EXTERNAL COMPONENTS MAX5090AATE CIN = 2 x 68F/100V EEVFK2A680Q, Panasonic CBYPASS = 0.47F/100V, GRM21BR72A474KA, Murata COUT = 220F/6.3V 6SVP220MX, Sanyo CBST = 0.22F/16V, GRM188R71C224K, Murata R1 = 0 R2 = Open RIN = 10, 1% (0603) D1 = PDS5100H, Diodes Inc. L1 = 47H, DO5022P-473 MAX5090BATE CIN = 2 x 68F/100V EEVFK2A680Q, Panasonic CBYPASS = 0.47F/100V, GRM21BR72A474KA, Murata COUT = 100F/6.3V 6SVP100M, Sanyo CBST = 0.22F/16V, GRM188R71C224K, Murata R1 = 0 R2 = Open RIN = 10, 1% (0603) D1 = PDS5100H, Diodes Inc. L1 = 47H, DO5022P-473
6.5 to 76
3.3
2
7.5 to 76
5
2
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
Table 2. Typical External Components Selection (Circuit of Figure 4) (continued)
VIN (V) VOUT (V) IOUT (A) EXTERNAL COMPONENTS MAX5090AATE CIN = 330F/50V EEVFK1H331Q, Panasonic CBYPASS = 0.47F/50V, GRM21BR71H474KA, Murata COUT = 100F/6.3V 6SVP100M, Sanyo CBST = 0.22F/16V, GRM188R71C224K, Murata R1 = 0 R2 = Open RIN = 10, 1% (0603) D1 = B360, Diodes Inc. L1 = 100H, DO5022P-104 MAX5090BATE CIN = 330F/50V EEVFK1H331Q, Panasonic CBYPASS = 0.47F/50V, GRM21BR71H474KA, Murata COUT = 100F/6.3V 6SVP100M, Sanyo CBST = 0.22F/16V, GRM188R71C224K, Murata R1 = 0 R2 = Open RIN = 10, 1% (0603) D1 = B360, Diodes Inc. L1 = 100H, DO5022P-104 MAX5090CATE (VOUT programmed to 11V) CIN = 330F/50V EEVFK1H331Q, Panasonic CBYPASS = 0.47F/50V, GRM21BR71H474KA, Murata COUT = 100F/16V 16SVP100M, Sanyo CBST = 0.22F/16V, GRM188R71C224K, Murata R1 = 910k R2 = 100k R3 = 88.2k, 1% (0603) R4 = 10k, 1% (0603) RIN = 10, 1% (0603) D1 = B360, Diodes Inc. L1 = 100H, DO5022P-104
MAX5090A/B/C
6.5 to 40
3.3
2
7.5 to 40
5
2
15 to 40
11
2
Table 3. Component Suppliers
SUPPLIER AVX Coilcraft Diodes Incorporated Panasonic Sanyo TDK Vishay WEBSITE www.avxcorp.com www.coilcraft.com www.diodes.com www.panasonic.com www.sanyo.com www.component.tdk.com www.vishay.com
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C
VIN 12V CIN 68F CBYPASS VIN ON/OFF PTC Rt Ct BST DRAIN LX CBST D1 B360 COUT 100F 100H
RIN VOUT 5V, 2A
MAX5090B
SYNC SGND PGND
FB SS VD 3.3F CSS
*LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENT AS POSSIBLE.
Figure 5. Load-Temperature Monitoring with ON/OFF (Requires Accurate VIN)
Chip Information
PROCESS: BCD TRANSISTOR COUNT: 7893
Ordering Information (continued)
PART TEMP RANGE PINPACKAGE* OUTPUT VOLTAGE (V) Adj Adj
MAX5090CATE+ -40C to +125C 16 TQFN-EP** MAX5090CATE -40C to +125C 16 TQFN-EP**
*The package code is T1655-3. **EP = Exposed pad. +Denotes lead-free package.
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2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters
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
MAX5090A/B/C
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 (c) 2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
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