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LTC3441 High Current Micropower Synchronous Buck-Boost DC/DC Converter
FEATURES
s s s s s
DESCRIPTIO
s s s s s s s s
Regulated Output with Input Above, Below or Equal to the Output Single Inductor, No Schottky Diodes High Efficiency: Up to 95% 25A Quiescent Current in Burst Mode(R) Operation Up to 1.2A Continuous Output Current from a Single Lithium-Ion True Output Disconnect in Shutdown 2.4V to 5.5V Input Range 2.4V to 5.25V Output Range 1MHz Fixed Frequency Operation Synchronizable Oscillator Selectable Burst Mode or Fixed Frequency Operation <1A Quiescent Current in Shutdown Small, Thermally Enhanced 12-Lead (4mm x 3mm) DFN package
The LTC(R)3441 is a high efficiency, fixed frequency, buckboost DC/DC converter that operates efficiently from input voltages above, below or equal to the output voltage. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for single lithium ion or multicell applications where the output voltage is within the battery voltage range. The device includes two 0.10 N-channel MOSFET switches and two 0.11 P-channel switches. External Schottky diodes are optional, and can be used for a moderate efficiency improvement. The operating frequency is internally set to 1MHz and can be synchronized up to 1.7MHz. Quiescent current is only 25A 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 is driven low or with a clock, then fixed frequency switching is enabled. Other features include a 1A shutdown, soft-start control, thermal shutdown and current limit. The LTC3441 is available in a thermally enhanced 12-lead (4mm x 3mm) DFN package.
APPLICATIO S
s s s s
Handheld Computers Handheld Instruments MP3 Players Digital Cameras
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
L1 4.7H 4 9 2.5V TO 4.2V 5 8
Li-Ion to 3.3V at 1A Buck-Boost Converter
VOUT 3.3V 1A 340k EFFICIENCY (%)
100 95 90 85 80 75 70 65
VOUT = 3.3V
SW1 PVIN VIN
SW2
10
Li-Ion
* CIN 10F
VOUT 12 LTC3441 FB 1 11 VC SHDN/SS 7 2 MODE/SYNC GND 3 6 PGND PGND
15k 1.5nF 200k
COUT 22F
60 55 50 2.5 3 3.5 4 VIN (V) 4.5 5 5.5
3441 TA02
*1 = Burst Mode OPERATION 0 = FIXED FREQUENCY
CIN: TAIYO YUDEN JMK212BJ106MG COUT: TAIYO YUDEN JMK325BJ226MM L1: TOKO A916CY-4R7M
3441 TA01
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Efficiency vs VIN
IOUT = 200mA IOUT = 1A
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1
LTC3441
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW SHDN/SS GND PGND SW1 SW2 PGND 1 2 3 4 5 6 13 12 FB 11 VC 10 VIN 9 8 7 PVIN VOUT MODE/SYNC
VIN, VOUT Voltage........................................ - 0.3V to 6V SW1, SW2 Voltage DC ...........................................................- 0.3V to 6V Pulsed < 100ns ...................................... - 0.3V to 7V SHDN/SS, MODE/SYNC Voltage ................. - 0.3V to 6V Operating Temperature Range (Note 2) .. - 40C to 85C Maximum Junction Temperature (Note 4) ........... 125C Storage Temperature Range ................ - 65C to 125C
ORDER PART NUMBER LTC3441EDE
DE12 PACKAGE 12-LEAD (4mm x 3mm) PLASTIC DFN TJMAX = 125C JA = 53C/W 1-LAYER BOARD JA = 43C/W 4-LAYER BOARD JC = 4.3C/W EXPOSED PAD IS PGND (PIN 13) MUST BE SOLDERED TO PCB
DE PART MARKING 3441
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER Input Start-Up 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 Input Current Limit Max Duty Cycle Min Duty Cycle Frequency Accuracy MODE/SYNC Threshold MODE/SYNC Input Current Error Amp AVOL Error Amp Source Current Error Amp Sink Current SHDN/SS Threshold SHDN/SS Threshold SHDN/SS Input Current VFB = 1.22V CONDITIONS
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT = 3.6V,unless otherwise noted.
MIN
q q q
TYP 2.3
MAX 2.4 5.25 1.25 50 40 1 900 7 10
UNITS V V V nA A A A A A A % %
2.4 1.19 1.22 1 25 0.1 520 0.1 0.1 0.10 0.11
VC = 0V, MODE/SYNC = 3V (Note 3) SHDN = 0V, Not Including Switch Leakage MODE/SYNC = 0V (Note 3) Switches B and C Switches A and D Switches B and C Switches A and D
q
2 70 100 0.85 0.4
3.2 88 0 1 0.01 90 14 300 1.15 1.4 1
Boost (% Switch C On) Buck (% Switch A In)
q q q q q
VMODE/SYNC = 5.5V
When IC is Enabled When EA is at Max Boost Duty Cycle VSHDN = 5.5V
q
0.4
1 2 0.01
1.4 2.4 1
2
U
% MHz V A dB A A V V A
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WW
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LTC3441
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3441E 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 measurements are preformed when the outputs are not switching. Note 4: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency
100 90 80 70 Burst Mode OPERATION VOUT 10mV/DIV AC-COUPLED BUCK VIN = 4.2V BUCK-BOOST VIN = 3.3V BOOST VIN = 2.7V
EFFICIENCY (%)
60 50 40 30 20 10 0 0.1 1 10 IOUT (mA) 100 1000
3441 G17
VIN = 2.7V
Load Transient Response, 100mA to 1A
VOUT 100mV/DIV
1A 100mA 100s/DIV
UW
VOUT Ripple at 1A Load
VIN = 4.2V VIN = 3.6V
L = 4.7H COUT = 47F IOUT = 1A VOUT = 3.3V
1s/DIV
3441 G02
Switch Pins in Buck-Boost Mode
Switch Pins Entering Buck-Boost Mode
SW1 2V/DIV
SW1 2V/DIV
SW2 2V/DIV
SW2 2V/DIV
3441 G01
VIN = 3.3V VOUT = 3.3V IOUT = 500mA
50ns/DIV
3441 G03
VIN = 4.2V VOUT = 3.3V IOUT = 500mA
50ns/DIV
3441 G04
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LTC3441 TYPICAL PERFOR A CE CHARACTERISTICS
Switch Pins Before Entering Boost Mode
630 620
VIN + VOUT CURRENT (A)
600 590 580 570 560 550 540 530 520 -55 -25 5 35 65 TEMPERATURE (C) 95 125
3441 G06
SW2 2V/DIV
VIN = 3V VOUT = 3.3V IOUT = 500mA
50ns/DIV
3441 G05
FEEDBACK VOLTAGE (V)
SW1 2V/DIV
Burst Mode Quiescent Current
50 VIN = VOUT = 3.6V
LINE REGULATION (dB)
40
80
EA SOURCE CURRENT (A)
VIN + VOUT CURRENT (A)
30
20
10 -55
-25
5 35 65 TEMPERATURE (C)
Error Amp Sink Current
400 VIN = VOUT = 3.6V 1.2
EA SINK CURRENT (A)
350
FREQUENCY (MHz)
CURRENT LIMIT (A)
300
250
200 -55
-25
5 35 65 TEMPERATURE (C)
4
UW
95
3441 G08
Active Quiescent Current
VIN = VOUT = 3.6V 1.241 1.236 1.231 1.226 1.221 1.216 1.211 1.206 1.201
Feedback Voltage
VIN = VOUT = 3.6V
610
1.196 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3441 G07
Feedback Voltage Line Regulation
90 VIN = VOUT = 2.4V TO 5.5V
20
Error Amp Source Current
VIN = VOUT = 3.6V
15
70
10
125
60 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3441 G09
5 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3441 G10
Output Frequency
VIN = VOUT = 3.6V
Current Limit
3.4 VIN = VOUT = 3.6V
1.1
3.2
1.0
3.0
0.9
95
125
3441 G11
0.8 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3441 G12
2.8 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3441 G13
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LTC3441 TYPICAL PERFOR A CE CHARACTERISTICS
NMOS RDS(ON)
0.15 VIN = VOUT = 3.6V SWITCHES B AND C 0.13 0.15 0.14 0.13 PMOS RDS(ON) () 0.12 0.11 0.10 0.09 0.08 0.07 0.06 0.05 -55 -25 5 35 65 TEMPERATURE (C) 95 125
3441 G14
MINIMUM START VOLTAGE (V)
NMOS RDS(ON) ()
0.11
0.09
0.07
PI FU CTIO S
SHDN/SS (Pin 1): Combined Soft-Start and Shutdown. Applied voltage < 0.4V shuts down the IC. Tie to >1.4V to enable the IC and >2.4V to ensure the error amp is not clamped from soft-start. An RC from the shutdown command signal to this pin will provide a soft-start function by limiting the rise time of the VC pin. GND (Pin 2): Signal Ground for the IC. PGND (Pins 3, 6, 13 Exposed Pad): Power Ground for the Internal NMOS Power Switches SW1 (Pin 4): Switch pin where the internal switches A and B are connected. Connect inductor from SW1 to SW2. An optional Schottky diode can be connected from this SW1 to ground. Minimize trace length to keep EMI down. SW2 (Pin 5): Switch pin where the internal switches C and D are connected. An optional Schottky diode can be connected from SW2 to VOUT (it is required where VOUT > 4.3V). Minimize trace length to keep EMI down. MODE/SYNC (Pin 7): Burst Mode Select and Oscillator Synchronization. MODE/SYNC = High: Enable Burst Mode Operation. During the period where the IC is supplying energy to the output, the inductor peak inductor current will reach 0.8A and return to zero current on each cycle. In Burst Mode operation the operation is variable frequency, which provides a significant efficiency improvement at light loads. The Burst Mode operation will continue until the pin is driven low. 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 between 100ns and 2s and a clock frequency between 2.3MHz and 3.4MHz (twice the desired frequency) is required to synchronize the IC. fOSC = fSYNC/2 VOUT (Pin 8): Output of the Synchronous Rectifier. A filter capacitor is placed from VOUT to GND. A ceramic bypass capacitor is recommended as close to the VOUT and GND pins as possible. PVIN (Pin 9): Power VIN Supply Pin. A 10F ceramic capacitor is recommended as close to the PVIN and PGND pins as possible VIN (Pin 10): Input Supply Pin. Internal VCC for the IC. VC (Pin 11): Error Amp Output. A frequency compensation network is connected from this pin to the FB pin to compensate the loop. See the section "Compensating the Feedback Loop" for guidelines. FB (Pin 12): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 2.4V to 5.25V. The feedback reference voltage is typically 1.22V.
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PMOS RDS(ON)
2.30 VIN = VOUT = 3.6V SWITCHES A AND D 2.25
Minimum Start Voltage
2.20
2.15
0.05 -50
-25
35 65 5 TEMPERATURE (C)
95
125
3441 G15
2.10 -55
-25
5 35 65 TEMPERATURE (C)
95
125
3441 G16
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5
LTC3441
BLOCK DIAGRA
VIN 2.4V TO 5.5V 9 PVIN VIN SW B
+
10
ISENSE AMP
+
gm = 1 k 100 3.2A PGND
-
AVERAGE CURRENT LIMIT THERMAL SHUTDOWN
SUPPLY CURRENT LIMIT
+
4A VCC INTERNAL
-
UVLO
+
2.4V
-
1MHz OSC SYNC SLEEP /2 5s DELAY 7 MODE/SYNC 2 GND 6 PGND Burst Mode OPERATION CONTROL SHUTDOWN
1 = Burst Mode OPERATION 0 = FIXED FREQUENCY
6
-
PWM LOGIC AND OUTPUT PHASING
PWM COMPARATORS CLAMP
+
-
-
+
+
W
SW1 SW A GATE DRIVERS AND ANTICROSS CONDUCTION 4 5 SW2 SW D VOUT VOUT 2.4V TO 5.25V 8 -0.8A SW C REVERSE CURRENT LIMIT ERROR AMP
+ -
1.22V R1 FB 12
VC
11 R2
SHDN/SS
RSS 1 VIN
CSS
3440 BD
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LTC3441
OPERATIO
The LTC3441 provides high efficiency, low noise power for applications such as portable instrumentation. The LTC proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amp output voltage on the VC pin determines the output duty cycle of the switches. Since the VC pin is a filtered signal, it provides rejection of frequencies from well below the switching frequency. The low RDS(ON), low gate charge synchronous switches provide high frequency pulse width modulation control at high efficiency. Schottky diodes across the synchronous switch D and synchronous switch B are not required, but provide a lower drop during the break-before-make time (typically 15ns). The addition of the Schottky diodes will improve peak efficiency by typically 1% to 2%. High efficiency is achieved at light loads when Burst Mode operation is entered and when the IC's quiescent current is a low 25A. LOW NOISE FIXED FREQUENCY OPERATION Oscillator The frequency of operation is factory trimmed to 1MHz. The oscillator can be synchronized with an external clock applied to the MODE/SYNC pin. A clock frequency of twice the desired switching frequency and with a pulse width of at least 100ns is applied. The oscillator sync range is 1.15MHz to 1.7MHz (2.3MHz to 3.4MHz sync frequency). Error Amp The error amplifier is a voltage mode amplifier. The loop compensation components are configured around the amplifier to obtain stability of the converter. The SHDN/SS pin will clamp the error amp output, VC, to provide a softstart function. Supply Current Limit The current limit amplifier will shut PMOS switch A off once the current exceeds 4A typical. Before the switch current limit, the average current limit amp (3.2A typical) will source current into the FB pin to drop the output voltage. The current amplifier delay to output is typically 50ns.
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Reverse Current Limit The reverse current limit amplifier monitors the inductor current from the output through switch D. Once a negative inductor current exceeds - 800mA typical, the IC will shut off switch D. Output Switch Control Figure 1 shows a simplified diagram of how the four internal switches are connected to the inductor, VIN, VOUT and GND. Figure 2 shows the regions of operation for the LTC3441 as a function of the internal control voltage, VCI. The VCI voltage is a level shifted voltage from the output of the error amp (VC pin) (see Figure 5). The output switches are properly phased so the transfer between operation modes is continuous, filtered and transparent to the user. When VIN approaches VOUT the Buck/Boost region is reached where the conduction time of the four switch region is typically 150ns. Referring to Figures 1 and 2, the various regions of operation will now be described.
PVIN 9 PMOS A SW1 4 NMOS B SW2 5 NMOS C VOUT 8 VOUT PMOS D
3441 F01
Figure 1. Simplified Diagram of Output Switches
75% DMAX BOOST A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK FOUR SWITCH PWM BUCK/BOOST REGION V2 (1.55V) D ON, C OFF PWM AB SWITCHES BUCK REGION 0% DUTY CYCLE V1 (0.9V) INTERNAL CONTROL VOLTAGE, VCI V3 (1.65V)
V4 (2.05V)
3441 F02
Figure 2. Switch Control vs Internal Control Voltage, VCI
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LTC3441
OPERATIO
Buck Region (VIN > VOUT) Switch D is always on and switch C is always off during this mode. When the internal control voltage, VCI, is above voltage V1, output A begins to switch. During the off time of switch A, synchronous switch B turns on for the remainder of the time. Switches A and B will alternate similar to a typical synchronous buck regulator. As the control voltage increases, the duty cycle of switch A increases until the maximum duty cycle of the converter in Buck mode reaches DMAX_BUCK, given by: DMAX_BUCK = 100 - D4SW % where D4SW = duty cycle % of the four switch range. D4SW = (150ns * f) * 100 % where f = operating frequency, Hz. Beyond this point the "four switch," or Buck/Boost region is reached. Buck/Boost or Four Switch (VIN ~ VOUT) When the internal control voltage, VCI, is above voltage V2, switch pair AD remain on for duty cycle DMAX_BUCK, and the switch pair AC begins to phase in. As switch pair AC phases in, switch pair BD phases out accordingly. When the VCI voltage reaches the edge of the Buck/Boost range, at voltage V3, the AC switch pair completely phase out the BD pair, and the boost phase begins at duty cycle D4SW. The input voltage, VIN, where the four switch region begins is given by:
VIN =
VOUT V 1 - (150ns * f)
The point at which the four switch region ends is given by: VIN = VOUT(1 - D) = VOUT(1 - 150ns * f) V Boost Region (VIN < VOUT) Switch A is always on and switch B is always off during this mode. When the internal control voltage, VCI, is above
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voltage V3, switch pair CD will alternately switch to provide a boosted output voltage. This operation is typical to a synchronous boost regulator. The maximum duty cycle of the converter is limited to 88% typical and is reached when VCI is above V4. 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 25A. In this mode the output ripple has a variable frequency component that depends upon load current. During the period where the device is delivering energy to the output, the peak current will be equal to 800mA typical and the inductor current will terminate at zero current for each cycle. In this mode the typical maximum average output current is given by:
IOUT(MAX)BURST
0.2 * VIN A VOUT + VIN
Burst Mode operation is user controlled, by driving the MODE/SYNC pin high to enable and low to disable. The peak efficiency during Burst Mode operation is less than the peak efficiency during fixed frequency because the part enters full-time 4-switch mode (when servicing the output) with discontinuous inductor current as illustrated in Figures 3 and 4. During Burst Mode operation, the control loop is nonlinear and cannot utilize the control voltage from the error amp to determine the control mode, therefore full-time 4-switch mode is required to maintain the Buck/Boost function. The efficiency below 1mA becomes dominated primarily by the quiescent current and not the peak efficiency. The equation is given by:
Efficiency Burst
( bm) * ILOAD 25A + ILOAD
where (bm) is typically 75% during Burst Mode operation.
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LTC3441
OPERATIO
Burst Mode Operation to Fixed Frequency Transient Response When transitioning from Burst Mode operation to fixed frequency, the system exhibits a transient since the modes of operation have changed. For most systems this transient is acceptable, but the application may have stringent input current and/or output voltage requirements that dictate a broad-band voltage loop to minimize the transient. Lowering the DC gain of the loop will facilitate the task (5M from FB to VC) at the expense of DC load regulation. Type 3 compensation is also recommended to broad band the loop and roll off past the two pole response of the LC of the converter (see Closing the Feedback Loop).
PVIN 9 A 4 SW1 B dI VIN L dt L D VOUT 8 A
+
-
IINDUCTOR
SW2 C
SW1 B 0mA T1
3441 F03
L
SW2 C
IINDUCTOR
6 GND
Figure 3. Inductor Charge Cycle During Burst Mode Operation
TO PWM COMPARATORS
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SOFT-START The soft-start function is combined with shutdown. When the SHDN/SS pin is brought above typically 1V, the IC is enabled but the EA duty cycle is clamped from the VC pin. A detailed diagram of this function is shown in Figure 5. The components RSS and CSS provide a slow ramping voltage on the SHDN/SS pin to provide a soft-start function.
PVIN 9 dI - VOUT L dt D 5 800mA VOUT 8 5 800mA 4
-
+
0mA T2
3441 F04
6 GND
Figure 4. Inductor Discharge Cycle During Burst Mode Operation
VIN 14A
ERROR AMP VOUT FB R1
+ -
SOFT-START CLAMP VCI
1.22V
12 VC 11 CP1 R2
SHDN/SS 1 CSS
RSS ENABLE SIGNAL
3441 F05
+
CHIP ENABLE
-
1V
Figure 5. Soft-Start Circuitry
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LTC3441
APPLICATIO S I FOR ATIO
COMPONENT SELECTION
1 SHDN/SS 2 GND 3 PGND 4 SW1 5 SW2 6 PGND FB 12 VC 11 VIN 10 PVIN 9 VOUT 8 MODE 7 VOUT VIN
GND
MULTIPLE VIAS
Figure 6. Recommended Component Placement. Traces Carrying High Current are Direct. Trace Area at FB and VC Pins are Kept Low. Lead Length to Battery Should be Kept Short. VOUT and VIN Ceramic Capacitors Close to the IC Pins
Inductor Selection The high frequency operation of the LTC3441 allows the use of small surface mount inductors. The inductor current ripple is typically set to 20% to 40% of the maximum inductor current. For a given ripple the inductance terms are given as follows:
L> L> VIN(MIN)2 * VOUT - VIN(MIN) * 100 f * IOUT(MAX) * %Ripple * VOUT2 VOUT * VIN(MAX) - VOUT * 100 f * IOUT(MAX) * %Ripple * VIN(MAX)
(
)
H,
(
)
H
where f = operating frequency, Hz %Ripple = allowable inductor current ripple, % VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V IOUT(MAX) = maximum output load current For high efficiency, choose an inductor with a high frequency core material, such as ferrite, to reduce core loses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses, and must be able to
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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 2 for a list of component suppliers.
Table 1. Inductor Vendor Information
SUPPLIER Coilcraft Coiltronics Murata
3441 F06
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PHONE (847) 639-6400 (561) 241-7876 USA: (814) 237-1431 (800) 831-9172
FAX (847) 639-1469 (561) 241-9339 USA: (814) 238-0490
WEB SITE www.coilcraft.com www.coiltronics.com www.murata.com
Sumida
USA: www.japanlink.com/ (847) 956-0666 (847) 956-0702 sumida Japan: 81(3) 3607-5111 81(3) 3607-5144
Output Capacitor Selection The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The steady state ripple due to charge is given by:
%Ripple _ Boost = %Ripple _ Buck = IOUT(MAX) * VOUT - VIN(MIN) * 100 COUT * VOUT * f
2
(
)
% %
IOUT(MAX) * VIN(MAX) - VOUT * 100 COUT * VIN(MAX) * VOUT * f
(
)
where COUT = output filter capacitor, F The output capacitance is usually many times larger in order to handle the transient response of the converter. For a rule of thumb, the ratio of the operating frequency to the unity-gain bandwidth of the converter is the amount the output capacitance will have to increase from the above calculations in order to maintain the desired transient response. The other component of ripple is due to the ESR (equivalent series resistance) of the output capacitor. Low ESR capacitors should be used to minimize output voltage ripple. For surface mount applications, Taiyo Yuden ceramic capacitors, AVX TPS series tantalum capacitors or Sanyo POSCAP are recommended.
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LTC3441
APPLICATIO S I FOR ATIO
Input Capacitor Selection Since the VIN pin is the supply voltage for the IC it is recommended to place at least a 4.7F, low ESR bypass capacitor.
Table 2. Capacitor Vendor Information
SUPPLIER AVX Sanyo PHONE (803) 448-9411 (619) 661-6322 FAX (803) 448-1943 (619) 661-1055 (408) 573-4159 WEB SITE www.avxcorp.com www.sanyovideo.com www.t-yuden.com
Taiyo Yuden (408) 573-4150
Optional Schottky Diodes The Schottky diodes across the synchronous switches B and D are not required (VOUT < 4.3V), but provide a lower drop during the break-before-make time (typically 15ns) of the NMOS to PMOS transition, improving efficiency. Use a Schottky diode such as an MBRM120T3 or equivalent. Do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency. For applications with an output voltage above 4.3V, a Schottky diode is required from SW2 to VOUT. Output Voltage < 2.4V The LTC3441 can operate as a buck converter with output voltages as low as 0.4V. The part is specified at 2.4V minimum to allow operation without the requirement of a Schottky diode. Synchronous switch D is powered from VOUT and the RDS(ON) will increase at low output voltages, therefore a Schottky diode is required from SW2 to VOUT to provide the conduction path to the output. Output Voltage > 4.3V A Schottky diode from SW to VOUT is required for output voltages over 4.3V. The diode must be located as close to the pins as possible in order to reduce the peak voltage on SW2 due to the parasitic lead and trace inductance. Input Voltage > 4.5V For applications with input voltages above 4.5V which could exhibit an overload or short-circuit condition, a 2/1nF series snubber is required between the SW1 pin and GND. A Schottky diode from SW1 to VIN should also be added as close to the pins as possible. For the higher
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input voltages, VIN bypassing becomes more critical; therefore, a ceramic bypass capacitor as close to the VIN and GND pins as possible is also required. Operating Frequency Selection Additional quiescent current due to the output switches GATE charge is given by: Buck: 800e-12 * VIN * f Boost: 400e-12 * (VIN + VOUT) * f Buck/Boost: f * (1200e-12 * VIN + 400e-12 * VOUT) where f = switching frequency Closing the Feedback Loop The LTC3441 incorporates voltage mode PWM control. The control to output gain varies with operation region (Buck, Boost, Buck/Boost), but is usually no greater than 15. The output filter exhibits a double pole response is given by:
fFILTER _ POLE = 1 Hz 2 * * L * COUT
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where COUT is the output filter capacitor. The output filter zero is given by:
fFILTER _ ZERO = 1 2 * * RESR * COUT Hz
where RESR is the capacitor equivalent series resistance. A troublesome feature in Boost mode is the right-half plane zero (RHP), and is given by:
fRHPZ
VIN = Hz 2 * * IOUT * L * VOUT
2
The loop gain is typically rolled off before the RHP zero frequency. A simple Type I compensation network can be incorporated to stabilize the loop but at a cost of reduced bandwidth and slower transient response. To ensure proper phase margin, the loop requires to be crossed over a decade before the LC double pole.
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LTC3441
APPLICATIO S I FOR ATIO
1 fUG = Hz 2 * * R1 * CP1 Most applications demand an improved transient response to allow a smaller output filter capacitor. To achieve a higher bandwidth, Type III compensation is required. Two zeros are required to compensate for the double-pole response.
1 Hz 2 * * 32 e3 * R1 * CP1 Which is extremely close to DC 1 fZERO1 = Hz 2 * * RZ * CP1 1 fZERO2 = Hz 2 * *R1 * CZ 1 fPOLE1 1 fPOLE2 = Hz 2 * * RZ * CP 2
The unity-gain frequency of the error amplifier with the Type I compensation is given by:
L1 4.7H 4 9 2.5V TO 4.2V 10 5 8 R1 348k R3 15k C4 220pF 5M R2 200k 220pF 2.2k
SW1 PVIN
SW2
Li-Ion
* CIN 10F
VOUT 12 LTC3441 VIN FB 1 11 SHDN/SS VC 7 2 MODE/SYNC GND 3 6 PGND PGND
*1 = Burst Mode OPERATION 0 = FIXED FREQUENCY
C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ476MM L1: TOKO A916CY-4R7M
Figure 9. Fast Transient Response Compensation for Step Load or Mode Change
12
U
VOUT
W
UU
+
ERROR AMP
1.22V FB 12 VC 11 CP1 R2
3441 F07
R1
-
Figure 7. Error Amplifier with Type I Compensation
VOUT
+
ERROR AMP
1.22V FB 12 VC 11 CP2
3441 F08
R1
CZ1
-
RZ
CP1
R2
Figure 8. Error Amplifier with Type III Compensation
VOUT 3.3V 1A
Load Transient Response, 100mA to 1A
C2 47F
VOUT 100mV/DIV
1A 100mA
3441 F09
100s/DIV
3441 G01
3441f
LTC3441
TYPICAL APPLICATIO S
Li-Ion to 3.3V at 1.2A Converter
L1 4.7H 4 9 2.8V TO 4.2V 10 5 8 R1 340k R3 15k C4 1.5nF D1 VOUT 3.3V 1.2A COUT 22F R2 200k
Li-Ion
*1 = Burst Mode OPERATION 0 = FIXED FREQUENCY
EFFICIENCY (%)
U
SW1 PVIN
SW2
D2 CIN 10F
*
VOUT 12 LTC3441 VIN FB 1 11 SHDN/SS VC 7 2 MODE/SYNC GND 3 6 PGND PGND
C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM D1, D2: ON SEMICONDUCTOR MBRM120LT3 L1: TOKO A916CY-3R3M
3441 TA03a
Efficiency
100 90 80 70 60 50 40 30 20 10 0 0.1 1 10 100 IOUT (mA) 1000 10000 2.7VIN PWM 4.2VIN PWM 3.6VIN PWM 4.2VIN BURST
3441 TA03b
3441f
13
LTC3441
TYPICAL APPLICATIO S
Li-Ion to 5V at Boost 600mA Boost Converter with Output Disconnect
L1 4.7H 4 9 2.5V TO 4.2V 1M Li-Ion 0.047F C1 10F * 10 5 8 D1 VOUT 5V 600mA R1 619k R3 15k C4 1.5nF COUT 22F R2 200k
*1 = Burst Mode OPERATION 0 = FIXED FREQUENCY
EFFICIENCY (%)
14
U
SW1 PVIN VIN
SW2
VOUT 12 LTC3441 FB 1 11 SHDN/SS VC 7 2 MODE/SYNC GND 3 6 PGND PGND
C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM D1: MBRM120LT3 L1: TOKO A916CY-4R7M
3441 TA04a
Efficiency
100 90 80 70 60 50 40 30 20 10 0 0.1 1 10 100 OUTPUT CURRENT (mA) 1000
3441 TA04b
VIN = 4.2V Burst Mode OPERATION VIN = 3.6 V VIN = 2.7V
3441f
LTC3441
PACKAGE DESCRIPTIO
3.50 0.05 1.70 0.05 2.20 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 3.30 0.05 (2 SIDES) 0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 0.10 (2 SIDES) R = 0.20 TYP 3.00 0.10 (2 SIDES) 1.70 0.10 (2 SIDES) PIN 1 NOTCH
(UE12/DE12) DFN 0603
PIN 1 TOP MARK (NOTE 6)
0.200 REF
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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
DE/UE Package 12-Lead Plastic DFN (4mm x 3mm)
(Reference LTC DWG # 05-08-1695)
0.65 0.05 7 R = 0.115 TYP 0.38 0.10 12 0.75 0.05 6 0.25 0.05 3.30 0.10 (2 SIDES) 1 0.50 BSC 0.00 - 0.05
3441f
15
LTC3441
TYPICAL APPLICATIO
VIN 2.5V TO 5.5V 1A MAX
RS 0.05
R4 1k
AVERAGE INPUT CURRENT CONTROL
RELATED PARTS
PART NUMBER LT 1613 LT1615/LT1615-1 LT1616 LTC1776 LTC1877 LTC1878 LTC1879 LT1930/LT1930A
(R)
DESCRIPTION 550mA (ISW) 1.4MHz High Efficiency Step-Up DC/DC Converter 300mA/80mA (ISW) Constant Off-Time, High Efficiency Step-Up DC/DC Converter 500mA (IOUT) 1.4MHz High Efficiency Step-Down DC/DC Converter 500mA (IOUT) 200kHz High Efficiency Step-Down DC/DC Converter 600mA (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 600mA (IOUT) 550kHz Synchronous Step-Down DC/DC Converter 1.2A (IOUT) 550kHz Synchronous Step-Down DC/DC Converter
1A (ISW) 1.2MHz/2.2MHz High Efficiency Step-Up DC/DC Converter VIN: 2.6V to 16V, VOUT(MAX): 34V, IQ: 5.5mA, ISD: 1A, ThinSOT 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 20A, ISD: 1A, ThinSOT 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 20A, ISD: 1A, ThinSOT 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 40A, ISD: 1A, 10-Lead MS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60A, ISD: 1A, 10-Lead MS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60A, ISD: 1A, TSSOP16E 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 2.5V, IQ: 25A, ISD: 1A, 10-Lead MS
3441f
LTC3405/LTC3405A 300mA (IOUT) 1.5MHz Synchronous Step-Down DC/DC Converter LTC3406/LTC3406B 600mA (IOUT) 1.5MHz Synchronous Step-Down DC/DC Converter LTC3407 LTC3411 LTC3412 LTC3440 600mA (IOUT) x2 1.5MHz Dual Synchronous Step-Down DC/DC Converter 1.25A (IOUT) 4MHz Synchronous Step-Down DC/DC Converter 2.5A (IOUT) 4MHz Synchronous Step-Down DC/DC Converter 600mA (IOUT) 2MHz Synchronous Buck-Boost DC/DC Converter
ThinSOT is a trademark of Linear Technology Corporation.
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
U
PCMCIA Powered GSM Modem
L1 10H 4 9 10 5 8 R6 24k 1N914 R1 392k VOUT 3.6V 2A (PULSED) SW1 PVIN VIN SW2 C1 10F VOUT 12 LTC3441 FB 1 11 VC SHDN/SS 7 2 MODE/SYNC GND 3 6 PGND PGND
+
1/2 LT1490A
-
C4 10nF R5 24k R2 200k
COUT 2200F
3441 TA05
-
1/2 LT1490A 2N3906 ICURRENTLIMIT = 1.22 * R4 R5 * RS
+
C1: TAIYO YUDEN JMK212BJ106MG C2: SANYO MV-AX SERIES L1: TOKO A916CY-4R7M
COMMENTS VIN: 0.9V to 10V, VOUT(MAX): 34V, IQ: 3mA, ISD: 1A, ThinSOTTM VIN: 1.2V to 15V, VOUT(MAX): 34V, IQ: 20A, ISD: 1A, ThinSOT High Efficiency, VIN: 3.6V to 25V, VOUT(MIN): 1.25V, IQ: 1.9mA, ISD: 1A, ThinSOT High Efficiency, VIN: 7.4V to 40V, VOUT(MIN): 1.24V, IQ: 3.2mA, ISD: 30A, N8, S8 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN): 0.8V, IQ: 10A, ISD: 1A, MS8 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 10A, ISD: 1A, MS8 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN): 0.8V, IQ: 15A, ISD: 1A, TSSOP16
LT/TP 0703 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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