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LTC3402 2A, 3MHz Micropower Synchronous Boost Converter
FEATURES
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DESCRIPTIO
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Synchronous Rectification: Up to 97% Efficiency 2A Switch Current Rating Fixed Frequency Operation Up to 3MHz Wide Input Range: 0.5V to 5V Very Low Quiescent Current: 38A (Burst Mode(R) Operation) 2.6V to 5.5V Adjustable Output Voltage 0.85V (Typ) Start-Up Voltage No External Schottky Diode Required (VOUT < 4.3V) Synchronizable Switching Frequency Burst Mode Enable Control Antiringing Control Reduces Switching Noise PGOOD Output OPTI-LOOP(R) Compensation Very Low Shutdown Current: < 1A Small 10-Pin MSOP Package
The LTC(R)3402 is a high efficiency, fixed frequency, stepup DC/DC converter that operates from an input voltage below 1V. The device includes a 0.16 N-channel MOSFET switch and a 0.18 P-channel synchronous rectifier. Switching frequencies up to 3MHz are programmed with an external timing resistor and the oscillator can be synchronized to an external clock. An external Schottky diode is optional but will slightly improve efficiency. Quiescent current is only 38A in Burst Mode operation, maximizing battery life in portable applications. Burst Mode operation is user controlled and can be enabled by driving the MODE/SYNC pin high. If the MODE/SYNC pin has either a clock or is driven low, then fixed frequency switching is enabled. Other features include a 1A shutdown, antiringing control, open-drain power good output, thermal shutdown and current limit. The LTC3402 is available in the 10-lead thermally enhanced MSOP package. Lower current applications should use the 1A rated LTC3401 synchronous boost converter. Applications that require VOUT < 2.6V should use the LTC3424.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Cellular Telephones Handheld Computers MP3 Players 2-Way Pagers GPS Receivers Battery Backup Supplies CCFL Backlights
TYPICAL APPLICATIO
VIN = 1.8V to 3V L1 2.2H
All Ceramic Capacitor 2-Cell to 3.3V at 1A Step-Up Converter
100
VOUT 3.3V 1A
90 80
EFFICIENCY (%)
Burst Mode OPERATION 1MHz CONSTANT FREQUENCY
3 10
LTC3402 VIN SHDN SW VOUT
4 7 8 9 5 C3 470pF R5 82k
R2 909k C2 44F (2 x 22F) R1 549k C4 4.7pF
70 60 50 40 30 20 10 0
+2
CELLS
2 6
MODE/SYNC FB PGOOD Rt VC GND
C1 10F
1
Rt 30.1k
VIN = 2.4V WITH SCHOTTKY 0.1 1 10 IOUT (mA) 100 1000
3402 TA02
C1: TAIYO YUDEN JMK212BJ106MG 0 = FIXED FREQ C2: TAIYO YUDEN JMK325BJ226MM 1 = Burst Mode OPERATION L1: COILCRAFT: D03316P-222
3402 TA01
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Efficiency
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LTC3402
ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW Rt MODE VIN SW GND 1 2 3 4 5 10 9 8 7 6 SHDN VC FB VOUT PGOOD
VIN, VOUT Voltages ...................................... - 0.5V to 6V SW Voltage ................................................. - 0.5V to 6V VC, Rt Voltages ......................... - 0.5V to (VOUT + 0.3V) PGOOD, SHDN, FB, MODE Voltages ........... - 0.5V to 6V Operating Temperature Range (Note 2) .. - 40C to 85C Storage Temperature Range ................. - 65C to 125C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC3402EMS MS PART MARKING LTSK
MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125C JA = 130C/ W 1 LAYER BOARD JA = 100C/ W 4 LAYER BOARD
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER Minimum Start-Up Voltage Minimum Operating Voltage Output Voltage Adjust Range Feedback Voltage Feedback Input Current Quiescent Current--Burst Mode Operation Quiescent Current--SHDN Quiescent Current--Active NMOS Switch Leakage PMOS Switch Leakage NMOS Switch On Resistance PMOS Switch On Resistance NMOS Current Limit NMOS Burst Current Limit Maximum Duty Cycle Minimum Duty Cycle Switching Frequency MODE/SYNC Input High MODE/SYNC Input Low MODE/SYNC Input Current Error Amp Transconductance PGOOD Threshold VMODE/SYNC = 5.5V I = - 5A to 5A, VC = VFB Referenced to Feedback Voltage -6 0.01 85 -9 - 12 Rt = 15k Rt = 15k
q q q q
CONDITIONS ILOAD = <1mA (Note 4)
q q q
MIN
TYP 0.85
MAX 1.0 0.5 5.5
UNITS V V V V nA A A A A A A A %
2.6 1.22 1.25 1 38 0.1 440 0.1 0.1 0.16 0.18 2 80 1.6 1.4 2.5 0.66 85
1.28 50 65 1 800 5 10
VFB = 1.25V VC = 0V, MODE/SYNC = 3.3V (Note 3) SHDN = 0V, Not Including Switch Leakage VC = 0V, MODE/SYNC = 0V, Rt = 300k (Note 3)
0 2 2.4 0.4 1
mhos %
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% MHz V V A
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LTC3402
ELECTRICAL CHARACTERISTICS
The q denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER PGOOD Low Voltage PGOOD Leakage SHDN Input High SHDN Input Low SHDN Input Current VSHDN = 5.5V 0.01 CONDITIONS IPGOOD = 1mA VOUT = 1V, IPGOOD = 20A VPGOOD = 5.5V VIN = VSHDN 1 0.4 1 MIN TYP 0.1 0.1 0.01 MAX 0.2 0.4 1 UNITS V V A V V A
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3402E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
Note 3: Current is measured into the VOUT pin since the supply current is bootstrapped to the output pin and in the application will reflect to the input supply by (VOUT/VIN) * Efficiency. The outputs are not switching. Note 4: Once the output is started, the IC is not dependent upon the VIN supply.
TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25C unless otherwise noted)
SW Pin and Inductor Current (IC) in Discontinuous Mode. Ringing Control Circuitry Eliminates High Frequency Ringing
IL 50mA/DIV 0A SW 1V/DIV
Switching Waveform on SW Pin
50ns/DIV
Transient Response 50mA to 500mA
VOUT AC 100mV/DIV
VOUT 200mV/DIV
550mA 50mA COUT = 22F L = 3.3H fOSC = 1MHz 200s/DIV
3402 G04
UW
Transient Response 5mA to 50mA
VOUT 100mV/DIV
SW 1V/DIV 50mA IOUT 0V
3402 G01
5mA 200ns/DIV
3402 G02
COUT = 22F L = 3.3H fOSC = 1MHz
200s/DIV
3402 G03
Burst Mode Operation
VOUT AC 100mV/DIV
Burst Mode Operation
SW 1V/DIV
SW 1V/DIV
VIN = 1.2V 5ms/DIV VOUT = 3.3V COUT = 100F IOUT = 250A MODE/SYNC PIN = HIGH
3402 G05
VIN = 1.2V 200s/DIV VOUT = 3.3V COUT = 100F IOUT = 20mA MODE/SYNC PIN = HIGH
3402 G06
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LTC3402 TYPICAL PERFOR A CE CHARACTERISTICS
Converter Efficiency 1.2V to 3.3V
100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0.1 1 10 100 OUTPUT CURRENT (mA) 1000
3402 G07
300kHz Burst Mode OPERATION 3MHz
EFFICIENCY (%)
60 50 40 30 20 10 0 0.1
EFFICIENCY (%)
1MHz
Start-Up Voltage vs IOUT
500 TA = 25C
14 12
OUTPUT CURRENT (mA)
400
EFFICIENCY LOSS (%)
300
CURRENT (A)
200
100
2
0 0.8 0.9 1 1.1 VIN (V) 1.2 1.3 1.4
3402 G09
EA FB Voltage
1.28 1.27 2.05
FREQUENCY (MHz) VOLTAGE (V)
1.26 1.25 1.24 1.23 1.22 -55
RESISTANCE ()
-15
65 TEMPERATURE (C)
25
4
UW
3402 G13
(TA = 25C unless otherwise noted) Converter Efficiency 3.6V to 5V
100 Burst Mode OPERATION 90
Converter Efficiency 2.4V to 3.3V
100 90 80 70 300kHz 3MHz 1MHz Burst Mode OPERATION
80 70 60 50 40 30 20 10 VIN = 3.6V 0.1 1 100 10 LOAD CURRENT (mA) 1000
3402 G10
1MHz FIXED FREQUENCY
1 10 100 OUTPUT CURRENT (mA)
1000
3402 G08
0
Efficiency Loss Without Schottky vs Frequency
TA = 25C
Current Limit
3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 -55
10 8 6 4
0 0.2
0.6
2.2 1.0 1.4 1.8 FREQUENCY (MHz)
2.6
3.0
-15
25 65 TEMPERATURE (C)
105 125
3402 G12
3402 G11
Oscillator Frequency Accuracy
2.10 Rt = 15k 0.30
NMOS RDS(ON)
VOUT = 3.3V
0.25
0.20
2.00
0.15
1.95
0.10
105 125
1.90 -55
-15
65 TEMPERATURE (C)
25
105 125
3402 G14
0.05 -55
-15
25 65 TEMPERATURE (C)
105 125
3402 G22
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LTC3402 TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25C unless otherwise noted)
PMOS RDS(ON)
0.30 VOUT = 3.3V 1.1
0.25
RESISTANCE ()
VOLTAGE (V)
0.20
0.9
VOLTAGE (V)
0.15
0.10
0.05 -55
-15
65 TEMPERATURE (C)
25
PGOOD Threshold
-7.0 -7.5 44 42 40
CURRENT (A)
PERCENT FROM VFB (%)
-8.0 -8.5 -9.0 -9.5
VOLTAGE (V)
-10.0
-10.5 -11.0 -11.5 -12.0 -55 -15 65 TEMPERATURE (C) 25 105 125
3402 G19
UW
Start-Up Voltage
1.10 1.05 1.0 1.00 0.95 0.90 0.85 0.80 0.75 0.7 0.70 0.65 105 125
3402 G16
Shutdown Threshold
0.8
0.6 -55
-15
65 TEMPERATURE (C)
25
105 125
3402 G17
0.60 -55
-15
25 65 TEMPERATURE (C)
105 125
3402 G18
Burst Mode Operation Current
2.50 2.45 2.40 2.35 2.30 2.25 2.20 2.15 2.10 32 30 -55 2.05 -15 65 TEMPERATURE (C) 25 105 125
3402 G20
VOUT Turn-Off Voltage
38 36 34
2.00 -55
-15
25 65 TEMPERATURE (C)
105 125
3402 G21
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LTC3402
PI FU CTIO S
Rt (Pin 1): Timing Resistor to Program the Oscillator Frequency.
fOSC = 3 * 1010 Hz Rt
MODE/SYNC (Pin 2): Burst Mode Select and Oscillator Synchronization. MODE/SYNC = High. Enable Burst Mode operation. The inductor peak inductor current will be 1/3 the current limit value and return to zero current on each cycle. During Burst Mode operation the operation is variable frequency, providing a significant efficiency improvement at light loads. It is recommended the Burst Mode operation only be entered once the part has started up. MODE/SYNC = Low. Disable Burst Mode operation and maintain low noise, constant frequency operation. MODE/SYNC = External CLK. Synchronization of the internal oscillator and Burst Mode operation disable. A clock pulse width of 100ns to 2s is required to synchronize. VIN (Pin 3): Input Supply Pin. SW (Pin 4): Switch Pin. Connect inductor and Schottky diode here. For applications with output voltages over 4.3V, a Schottky diode is required to ensure that the SW pin voltage does not exceed its absolute maximum rating. Minimize trace length to keep EMI and high ringing down. For discontinuous inductor current, a controlled impedance is placed from SW to VIN from the
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IC to eliminate high frequency ringing due to the resonant tank of the inductor and SW node capacitance, therefore reducing EMI radiation. GND (Pin 5): Signal and Power Ground for the IC. PGOOD (Pin 6): Power Good Comparator Output. This open-drain output is low when VFB < - 9% from its regulation voltage. VOUT (Pin 7): Output of the Synchronous Rectifier and Bootstrapped Power Source for the IC. A ceramic capacitor of at least 1F is required and should be located as close to the VOUT and GND pins as possible (Pins 7 and 5). FB (Pin 8): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 2.6V to 5V. The feedback reference voltage is typically 1.25V. VC (Pin 9): Error Amp Output. A frequency compensation network is connected to this pin to compensate the loop. See the section "Compensating the Feedback Loop" for guidelines. SHDN (Pin 10): Shutdown. Grounding this pin shuts down the IC. Tie to >1V to enable (VIN or digital gate output). To operate with input voltages below 1V once the converter has started, a 1M resistor from SHDN to VIN and a 5M resistor from SHDN to VOUT will provide sufficient hysteresis. During shutdown, the output voltage will hold up to VIN minus a diode drop due to the body diode of the PMOS synchronous switch. If the application requires a complete disconnect during shutdown, refer to the section "Output Disconnect Circuits."
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LTC3402
BLOCK DIAGRA
3
VIN ANTIRING
SHDN 10
SHUTDOWN
GND
5
PWM LOGIC SLEEP
+
-
9 Burst Mode CONTROL
Rt
1
OSC SLOPE COMP
POK 6 N
1.25V - 9%
3402 BD
-
CURRENT COMP
ERROR AMP 8
+
-
-
+
+
-
+
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+
1V TO VOUT + 0.3V 4 SW P VOUT 7 VOUT 2.6V TO 5.5V ANTICROSS COND N
+
ISENSE AMP
10mV
+ -
IZERO AMP
-
CURRENT LIMIT
+
2.8A TYP
1.25V R1 FB
VC
R2
2 MODE/SYNC
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LTC3402
APPLICATIO S I FOR ATIO
DETAILED DESCRIPTION
The LTC3402 provides high efficiency, low noise power for applications such as portable instrumentation. The current mode architecture with adaptive slope compensation provides ease of loop compensation with excellent transient load response. The low RDS(ON), low gate charge synchronous switches provide the pulse width modulation control at high efficiency. The Schottky diode across the synchronous PMOS switch provides a lower drop during the break-before-make time (typically 20ns) of the NMOS to PMOS transition. The addition of the Schottky diode will improve efficiency (see graph "Efficiency Loss Without Schottky vs Frequency"). While the IC's quiescent current is a low 38A, high efficiency is achieved at light loads when Burst Mode operation is entered. Low Voltage Start-Up The LTC3402 is designed to start up at input voltages of typically 0.85V. The device can start up under some load, (see graph Start-Up vs Input Voltage). Once the output voltage exceeds a threshold of 2.3V, then the IC powers itself from VOUT instead of VIN. At this point, the internal circuitry has no dependency on the input voltage, eliminating the requirement for a large input capacitor. The input voltage can drop below 0.5V without affecting the operation, but the limiting factor for the application becomes the availability of the power source to supply sufficient energy to the output at the low voltages. Low Noise Fixed Frequency Operation Oscillator. The frequency of operation is set through a resistor from the Rt pin to ground where f = 3 * 1010/Rt. An internally trimmed timing capacitor resides inside the IC. The oscillator can be synchronized with an external clock inserted on the MODE/SYNC pin. When synchronizing the oscillator, the free running frequency must be set to approximately 30% lower than the desired synchronized frequency. Keeping the sync pulse width below 2s will ensure that Burst Mode operation is disabled. Current Sensing. Lossless current sensing converts the peak current signal to a voltage to sum in with the internal slope compensation. This summed signal is compared to
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the error amplifier output to provide a peak current control command for the PWM. The slope compensation in the IC is adaptive to the input and output voltage. Therefore, the converter provides the proper amount of slope compensation to ensure stability and not an excess causing a loss of phase margin in the converter. Error Amp. The error amplifier is a transconductance amplifier with gm = 0.1ms. A simple compensation network is placed from the VC pin to ground. Current Limit. The current limit amplifier will shut the NMOS switch off once the current exceeds its threshold. The current amplifier delay to output is typically 50ns. Zero Current Amp. The zero current amplifier monitors the inductor current to the output and shuts off the synchronous rectifier once the current is below 50mA, preventing negative inductor current. Antiringing Control. The anitringing control will place an impedance across the inductor to damp the ringing on the SW pin during discontinuous mode operation. The LCSW ringing (L = inductor, CSW = capacitance on the switch pin) is low energy, but can cause EMI radiation. Burst Mode Operation Burst Mode operation is when the IC delivers energy to the output until it is regulated and then goes into a sleep mode where the outputs are off and the IC is consuming only 38A. In this mode, the output ripple has a variable frequency component with load current and the steady state ripple will be typically below 3%. During the period where the device is delivering energy to the output, the peak current will be equal to 1/6 the current limit value and the inductor current will terminate at zero current for each cycle. In this mode the maximum output current is given by:
I OUT(MAXBURST) VIN Amps 6 * VOUT
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Burst Mode operation is user controlled by driving the MODE/SYNC pin high to enable and low to disable. It is recommended that Burst Mode operation be entered after the part has started up.
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LTC3402
APPLICATIO S I FOR ATIO
COMPONENT SELECTION Inductor Selection
The high frequency operation of the LTC3402 allows the use of small surface mount inductors. The minimum inductance value is proportional to the operating frequency and is limited by the following constraints:
VIN(MIN) * VOUT(MAX) - VIN(MIN) 2 L > H and L > H f f * Ripple * VOUT(MAX)
(
where f = Operating Frequency (Hz) Ripple = Allowable Inductor Current Ripple (A) VIN(MIN) = Minimum Input Voltage (V) VOUT(MAX) = Maximum Output Voltage (V) The inductor current ripple is typically set to 20% to 40% of the maximum inductor current.
SHDN Rt MODE VC VIN FB SW VOUT GND POK
VOUT
3402 F01
Figure 1. Recommended Component Placement. Traces Carrying High Current Are Direct. Trace Area FB and VC Pins Are Kept Low. Lead Length to Battery Should be Kept Short
For high efficiency, choose an inductor with a high frequency core material, such as ferrite, to reduce core losses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses and must be able to handle the peak inductor current without saturating. Molded chokes or chip inductors usually do not have enough core to support the peak inductor currents in the 1A to 2A region. To minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. See Table 1 for suggested components and Table 1 for a list of component suppliers.
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Table 1. Inductor Vendor Information
SUPPLIER Coilcraft Coiltronics Murata Sumida USA: (847) 956-0666 (847) 956-0702 Japan: 81-3-3607-5111 81-3-3607-5144 www.japanlink.com sumida PHONE (847) 639-6400 (516) 241-7876 (814) 237-1431 (800) 831-9172 FAX (847) 639-1469 (516) 241-9339 (814) 238-0490 WEBSITE www.coilcraft.com www.coiltronics.com www.murata.com
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Output Capacitor Selection The output voltage ripple has several components. The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The max ripple due to charge is given by:
VRBULK =
where
IP * VIN V COUT * VOUT * f
IP = Peak Inductor Current The ESR can be a significant factor for ripple in most power converters. The ripple due to capacitor ESR is simply given by: VRCESR = IP * RESR V where RESR = Capacitor Series Resistance Low ESR capacitors should be used to minimize output voltage ripple. For surface mount applications, AVX TPS series tantalum capacitors and Sanyo POSCAP or TaiyoYuden ceramic X5R or X7R type capacitors are recommended. For through-hole applications Sanyo OS-CON capacitors offer low ESR in a small package size. See Table 2 for a list of component suppliers. In some layouts it may be required to place a 1F low ESR capacitor as close to the VOUT and GND pins as possible.
Table 2. Capacitor Vendor Information
SUPPLIER AVX Sanyo Taiyo Yuden PHONE (803) 448-9411 (619) 661-6322 (408) 573-4150 FAX (803) 448-1943 (619) 661-1055 (408) 573-4159 WEBSITE www.avxcorp.com www.sanyovideo.com www.t-yuden.com
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LTC3402
APPLICATIO S I FOR ATIO
Input Capacitor Selection
The input filter capacitor reduces peak currents drawn from the input source and reduces input switching noise. Since the IC can operate at voltages below 0.5V once the output is regulated, then demand on the input capacitor is much less and in most applications a 4.7F is recommended. Output Diode For applications with output voltages over 4.3V, a Schottky diode is required to ensure that the SW pin voltage does not exceed its absolute maximum rating. The Schottky diode across the synchronous PMOS switch provides a lower drop during the break-before-make time (typically 20ns) of the NMOS to PMOS transition. The Schottky diode improves peak efficiency (see graph "Efficiency Loss Without Schottky vs Frequency). Use of a Schottky diode such as a MBR0520L, 1N5817 or equivalent. Since slow recovery times will compromise efficiency, do not use ordinary rectifier diodes. Operating Frequency Selection There are several considerations in selecting the operating frequency of the converter. The first is determining the sensitive frequency bands that cannot tolerate any spectral noise. For example, in products incorporating RF communications, the 455kHz IF frequency is sensitive to any noise, therefore switching above 600kHz is desired. Some communications have sensitivity to 1.1MHz. In this case, a 2MHz converter frequency may be employed. The second consideration is the physical size of the converter. As the operating frequency goes up, the inductor and filter caps go down in value and size. The trade off is in efficiency since the switching losses due to gate charge are going up proportional with frequency. For example in Figure 2, for a 2.4V to 3.3V converter, the efficiency at 100mA is 5% less at 2MHz compared to 300kHz. Another operating frequency consideration is whether the application can allow "pulse skipping." In this mode, the minimum on time of the converter cannot support the duty cycle, so the converter ripple will go up and there will be a low frequency component of the output ripple. In many
EFFICIENCY (%)
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applications where physical size is the main criterion then running the converter in this mode is acceptable. In applications where it is preferred not to enter this mode, then the maximum operating frequency is given by:
fMAX _ NOSKIP = VOUT - VIN Hz VOUT * tON(MIN)
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where tON(MIN) = minimum on time = 120ns.
100 90 80 70 60 50 40 30 20 10 0 0.1 1 10 100 OUTPUT CURRENT (mA) 1000
3402 G08
Burst Mode OPERATION 3MHz 300kHz 1MHz
Figure 2. Converter Efficiency 2.4V to 3.3V
Reducing Output Capacitance with a Load Feed Forward Signal In many applications the output filter capacitance can be reduced for the desired transient response by having the device commanding the change in load current, (i.e. system microcontroller), inform the power converter of the changes as they occur. Specifically, a "load feed forward" signal coupled into the VC pin gives the inner current loop a head start in providing the change in output current. The transconductance of the LTC3402 converter at the VC pin with respect to the inductor current is typically 170mA/100mV, so the amount of signal injected is proportional to the anticipated change of inductor current with load. The outer voltage loop performs the remainder of the correction, but because of the load feed forward signal, the range over which it must slew is greatly reduced. This results in an improved transient response. A logic level feed forward signal, VFF, is coupled through components C5 and R6. The amount of feed forward
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LTC3402
APPLICATIO S I FOR ATIO
signal is attenuated with resistor R6 and is given by the following relationship:
V * R5 * VIN * 1.5 R6 FF - R5 VOUT * IOUT
where IOUT = load current change.
VIN 3 10 2 6 1 LTC3402 VIN SHDN SW VOUT 4 7 8 9 5 C3 VOUT
MODE/SYNC FB PGOOD Rt VC GND
R5 C5 3.3nF
3402 F03
LOAD FEED FORWARD SIGNAL
R6 VFF
Figure 3
Closing the Feedback Loop The LTC3402 used current mode control with internal adaptive slope compensation. Current mode control eliminates the 2nd order filter due to the inductor and output capacitor exhibited in voltage mode controllers, and simplifies it to a single-pole filter response. The product of the modulator control to output DC gain plus the error amp open-loop gain equals the DC gain of the system. GDC = GCONTROLOUTPUT * GEA
2 * VIN GCONTROL = , GEA 2000 IOUT
The output filter pole is given by:
fFILTERPOLE = IOUT Hz * VOUT * COUT
where COUT is the output filter capacitor.
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The output filter zero is given by:
fFILTERZERO = 1 2 * * RESR * COUT Hz
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where RESR is the capacitor equivalent series resistance. A troublesome feature of the boost regulator topology is the right half plane zero (RHP) and is given by:
fRHPZ = VIN RO
2 2LVO 2
Hz
At heavy loads this gain increase with phase lag can occur at a relatively low frequency. The loop gain is typically rolled off before the RHP zero frequency. The typical error amp compensation is shown in Figure 4. The equations for the loop dynamics are as follows:
fPOLE1
1 Hz 2 * * 20 * 106 * CC1
which is extremelyclose to DC 1 Hz 2 * * RZ * CC1 1 fPOLE2 Hz 2 * * RZ * CC2 f ZERO1 =
Refer to AN76 for more closed-loop examples.
VOUT
+
ERROR AMP
1.25V FB 8 VC 9 CC1 RZ
3402 F04
R1
-
R2
CC2
Figure 4
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LTC3402
OUTPUT DISCO
VIN = 1.8V TO 3V LTC3402 VIN SHDN SW VOUT
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ECT CIRCUITS
Single Cell Output Disconnect
ZETEX FMMT717
VIN = 0.9V TO 1.5V LTC3402 VIN SHDN SW VOUT
VOUT
3 10 2 6 1
4 7 8 9 5
RB*
MODE/SYNC FB PGOOD Rt VC GND
C5 1F
3402 TA03
(V - VINMIN - 0.7V) * 100 *SET RB TO FORCE BETA OF 100; RB = OUT IOUTMAX 0 = FIXED FREQUENCY 1 = Burst Mode OPERATION
Dual Cell Output Disconnect Allowing Full Load Start-Up
IRLML6401 VOUT 3 10 2 6 1 4 7 8 9 5 2N2222 C5 1F RG 1M
R7 1M
MODE/SYNC FB PGOOD Rt VC GND
3402 TA04
0 = FIXED FREQUENCY 1 = Burst Mode OPERATION
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TYPICAL APPLICATIO S
Single Cell to 3V at 500mA, All Ceramic Capacitor, 3MHz Step-Up Converter
90
D1 VOUT 3V 500mA R2 866k
VIN = 0.9V TO 1.5V
L1 2.2H
R4 5.1M
3 10
VIN SHDN
SW VOUT
4 7 8 9 5 C3 470pF R5 39k
EFFICIENCY (%)
R3 1M
LTC3402
+1
CELL
2 6
MODE/SYNC FB PGOOD Rt VC GND
C1 3.3F
1
Rt 10k
0 = FIXED FREQUENCY 1 = Burst Mode OPERATION
C1: TAIYO YUDEN JMK212BJ335MG C2: TAIYO YUDEN JMK325BJ106MM D1: ON SEMICONDUCTOR MBRM120T3 L1: COILCRAFT DO1608-222
Li-Ion to 5V at 300mA, 1MHz Step-Up Converter
L1 10H D1*
100
VIN = 2.5V TO 4.2V
EFFICIENCY (%)
R3 1M
3 10
LTC3402 VIN SHDN SW VOUT
Li-Ion C1 4.7F
2 6 1
MODE/SYNC FB PGOOD Rt VC GND
Rt 30.1k
0 = FIXED FREQUENCY 1 = Burst Mode OPERATION
*LOCATE COMPONENTS AS CLOSE TO IC AS POSSIBLE C1: TAIYO YUDEN JMK212BJ475MG C2: TAIYO YUDEN JMK325BJ226MM D1: ON SEMICONDUCTOR MBRM120T3 L1: SUMIDA CDH53-100
U
4 7 8 9 5
Efficiency
80 70 60 50 40 30 20
Burst Mode OPERATION 3MHz FIXED FREQUENCY
C2 10F
C4 20pF
R1 619k
10 0 0.1 1 10 100 OUTPUT CURRENT (mA) 1000
3402 TA05b
3404 TA05a
Efficiency
VOUT 5V 600mA
Burst Mode OPERATION
90 80 70 60 50 40 30 1MHz FIXED FREQUENCY
R2 1.65M
C2* 22F C3 470pF R5 82k C4 4.7pF R1 549k
20 10 0 VIN = 3.6V 0.1 1 100 10 LOAD CURRENT (mA) 1000
3402 G10 3402 TA07a
3402fa
13
LTC3402
TYPICAL APPLICATIO S
High Efficiency, Compact CCFL Supply with Remote Dimming
VIN = 2.5V TO 4.2V
C1 10F
C1: TAIYO YUDEN JMK212BJ106MG C2: PANASONIC ECH-U D1: ZETEX ZHCS-1000 D2 TO D4: 1N4148
14
U
C3 27pF 1kV
T1 1 10 2
6
5
3
4
R1 300
CCFL C2 Q1 0.22F Q2 L1 33F
D1
D4
R4 20k
DIMMING INPUT 0V TO 2.5V
R5 Li-Ion 1M
3 10 2 6 1
LTC3402 VIN SHDN SW VOUT
4 7 D2 8 9 5 C5 1F C4 0.1F
3402 TA06
D3
MODE/SYNC FB PGOOD Rt VC GND
R2 10k R3 1k
Rt 150k
L1: SUMIDA CD-54-330MC Q1, Q2: ZETEX FMMT-617 T1: SUMIDA C1Q122
CCFL BACKLIGHT APPLICATION CIRCUITS CONTAINED IN THIS DATA SHEET ARE COVERED BY U.S. PATENT NUMBER 5408162 AND OTHER PATENTS PENDING
3402fa
LTC3402
PACKAGE DESCRIPTION
MS Package 10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661)
5.23 (.206) MIN
0.50 0.305 0.038 (.0197) (.0120 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
0.254 (.010) GAUGE PLANE
0.18 (.007) SEATING PLANE 0.17 - 0.27 (.007 - .011) 0.13 0.05 (.005 .002)
MSOP (MS) 0402
NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
0.889 0.127 (.035 .005)
3.2 - 3.45 (.126 - .136) 3.00 0.102 (.118 .004) (NOTE 3) 10 9 8 7 6
0.497 0.076 (.0196 .003) REF
DETAIL "A" 0 - 6 TYP
4.88 0.10 (.192 .004)
3.00 0.102 (.118 .004) NOTE 4
12345 0.53 0.01 (.021 .006) DETAIL "A" 1.10 (.043) MAX 0.86 (.034) REF
0.50 (.0197) TYP
3402fa
15
LTC3402
TYPICAL APPLICATIO
VIN =1.8V TO 3V
+
2 CELLS
C1 4.7F
0 = FIXED FREQ 1 = Burst Mode OPERATION
C1: TAIYO YUDEN JMK212BJ475MG C2: TAIYO YUDEN JMK325BJ226MM D1: ON SEMICONDUCTOR MBRM120T3 D2 TO D7: ZETEX FMND7000 DUAL DIODE L1: SUMIDA CD43-2R2M
RELATED PARTS
PART NUMBER LT(R)1306 LT1308A/LT1308B LT1613 LT1615 LT1619 LTC1872 LT1930/LT1930A LT1949 LTC3400 LTC3401 LTC3424 DESCRIPTION Sync, Fixed Frequency, Step-Up DC/DC Converter High Current, Micropower, Single Cell 600kHz DC/DC Converter 1.4MHz, Single Cell DC/DC Converter in SOT-23 Micropower Step-Up DC/DC Converter in SOT-23 High Efficiency Boost DC/DC Controller SOT-23 Boost DC/DC Controller 1.2MHz/2.2MHz DC/DC Converters in SOT-23 600kHz, 1A Switch PWM DC/DC Converter Single Cell, High Current (600mA), Micropower, Synchronous 1.2MHz Step-Up DC/DC Converter Single Cell, High Current (1A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter Single Cell, High Current (2A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter COMMENTS Internal 2A Switches; VIN As Low As 1.8V 5V at 1A with Single Li-Ion Cell, VOUT to 34V VIN As Low As 1.1V, 3V at 30mA from Single Cell IQ = 20A, 1A Shutdown Current, VIN As Low As 1V 1A Gate Drive, 1.1V to 20V Input, Separate VCC for Gate Drive 550kHz, 2.5V to 9.8V Input VIN = 2.6V to 16V, 5V at 450mA from 3.3V Input 1A, 0.5, 30V Internal Switch, VIN As Low As 1.5V, Low-Battery Detect Active in Shutdown VIN = 0.85V to 5.5V, Up to 92% Efficiency Synchronizable Oscillator from 100kHz to 1.2MHz, ThinSOT Package VIN = 0.5V to 5V, Up to 97% Efficiency Synchronizable Oscillator from 100kHz to 3MHz, 10-Lead MSOP Package VOUT = 1.5V, Up to 97% Efficiency Synchronizable Oscillator from 100kHz to 3MHz, 10-Lead MSOP Package
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
U
Triple Output Converter
D2 D3 D4 D5 8V 2mA 0.1F 0.1F 0.1F 4.7F L1 2.2H D1 VOUT 3.3V 500mA R2 909k R3 1M 3 10 2 6 1 LTC3402 VIN SHDN SW VOUT 4 7 8 9 5 C3 470pF R5 82k R1 549k C4 4.7pF C2 22F MODE/SYNC FB PGOOD Rt VC GND Rt 30.1k
3402 TA08
0.1F D6 4.7F D7 -2.5V 1mA
3402fa LT/TP 0502 1.5K REV A * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2000

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