LTC3772B
Micropower No RSENSE
Constant Frequency Step-Down
DC/DC Controller
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FEATURES
DESCRIPTIO
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The LTC®3772B is a constant frequency current mode
step-down DC/DC controller in a low profile 8-lead SOT-23
(ThinSOTTM) and a 3mm × 2mm DFN package. The No
RSENSETM architecture eliminates the need for a current
sense resistor, improving efficiency and saving board
space.
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No Current Sense Resistor Required
High Output Currents Easily Achieved
Internal Soft-Start Ramps VOUT
Wide VIN Range: 2.75V to 9.8V
Low Dropout: 100% Duty Cycle
Constant Frequency 550kHz Operation
Low Ripple Pulse Skipping Operation at Light Load
Output Voltage as Low as 0.8V
±1.5% Voltage Reference Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
Only 8µA Supply Current in Shutdown
Low Profile 8-Lead SOT-23 (1mm) and
(3mm × 2mm) DFN (0.75mm) Packages
The LTC3772B automatically switches into pulse skipping
operation at light loads. It consumes only 200µA of quiescent current under a no-load condition.
The LTC3772B incorporates an undervoltage lockout feature that shuts down the device when the input voltage
falls below 2V. To maximize the runtime from a battery
source, the external P-channel MOSFET is turned on
continuously in dropout (100% duty cycle). High switching frequency of 550kHz allows the use of a small inductor
and capacitors. An internal soft-start smoothly ramps the
output voltage from zero to its regulation point.
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APPLICATIO S
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1- or 2-Cell Li-Ion Battery-Powered Applications
Wireless Devices
Portable Computers
Distributed Power Systems
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
ThinSOT and No RSENSE are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by
U.S. Patents including 5731694, 6127815.
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TYPICAL APPLICATIO
Efficiency and Power Loss vs Load Current
(Figure 5 Circuit)
550kHz Micropower Step-Down DC/DC Converter
ITH/RUN
VIN
2.75V TO 9.8V
VIN
LTC3772B
SW
47µF
VOUT
2.5V
2A
174k
60
0.1
50
40
POWER LOSS
30
3772B TA01
1
EFFICIENCY
70
3.3µH
VFB
80
10µF
PGATE
82.5k
90
POWER LOSS (W)
GND
22pF
10
100
20k
EFFICIENCY (%)
680pF
0.01
20
VIN = 3.3V
VIN = 5V
10
0
1
10
100
1000
LOAD CURRENT (mA)
0.001
10000
3772B TA01b
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1
LTC3772B
W W
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W
ABSOLUTE MAXIMUM RATINGS (Note 1)
Input Supply Voltage (VIN)........................ – 0.3V to 10V
IPRG Voltage ............................... – 0.3V to (VIN + 0.3V)
VFB, ITH/RUN Voltages ............................. – 0.3V to 2.4V
SW Voltage ........... – 2V to (VIN + 1V) or 10V Maximum
PGATE Peak Output Current (1µF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25)(CLOAD).
Thus a 10µF capacitor would require a 250µs rise time,
limiting the charging current to about 200mA.
Minimum On-Time Considerations
Minimum on-time, tON(MIN), is the smallest amount of
time that the LTC3772B is capable of turning the top
MOSFET on and then off. It is determined by internal
timing delays and the gate charge required to turn on the
top MOSFET. The minimum on-time for the LTC3772B is
about 250ns. Low duty cycle and high frequency applications may approach this minimum on-time limit and care
should be taken to ensure that:
tON(MIN) <
VOUT
f • VIN
If the duty cycle falls below what can be accommodated by
the minimum on-time, the LTC3772B will begin to skip
cycles. The output voltage will continue to be regulated,
but the ripple current and ripple voltage will increase.
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LTC3772B
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TYPICAL APPLICATIO S
550kHz Micropower, 1A, 2-Cell Li-Ion to 3.3VOUT
Step-Down DC/DC Converter
100pF
15k
ITH/RUN
VIN
CIN
22µF
LTC3772B
GND
56.2k
Si2341DS
PGATE
IPRG
L1 4.7µH
VFB
SW
UPS120
22pF
VIN
5V TO 8.4V
COUT
47µF
VOUT
3.3V
1A
174k
3772B TA02a
L1: SUMIDA CR43-4R7
CIN: MURATA GRM32ER61C226KA65B
COUT: MURATA GRM32ER60J476ME20B
Efficiency vs Load Current
100
VIN = 5.5V
90
EFFICIENCY (%)
VIN = 7.2V
80
VIN = 8.4V
70
60
50
40
1
10
100
1000
LOAD CURRENT (mA)
10000
3772B TA02b
Start-Up
Load Step
VOUT
2V/DIV
VOUT
100mV/DIV
(AC)
ITH/RUN
1V/DIV
IL
500mA/DIV
IL
1A/DIV
ILOAD
500mA/DIV
VIN = 5.5V
VOUT = 3.3V
RLOAD = 3Ω
400µs/DIV
3772B TA02c
20µs/DIV
VIN = 5.5V
VOUT = 3.3V
ILOAD = 40mA TO 500mA
3772B TA02d
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LTC3772B
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TYPICAL APPLICATIO S
550kHz Micropower 3A Step-Down DC/DC Converter
220pF
34.8k
ITH/RUN
VIN
CIN
22µF
LTC3772B
GND
PGATE
IPRG
82.5k
VFB
NTMS5PO2R2
L1 2.2µH
SW
COUT
100µF
×2
B320A
22pF
VIN
2.75V TO 9.8V
174k
VOUT
2.5V
3A
3772B TA03a
L1: VISHAY IHLP-2525CZ-01
CIN: GRM32ER61A220KA65B
COUT: TAIYO YUDEN LDK375BJ107MM
Efficiency vs Load Current
100
90
EFFICIENCY (%)
VIN = 3.3V
80
VIN = 5V
70
60
50
40
1
100
1000
10
LOAD CURRENT (mA)
10000
3772B TA03b
Start-Up
Load Step
VOUT
2V/DIV
VOUT
100mV/DIV
(AC)
ITH/RUN
1V/DIV
IL
2A/DIV
IL
2A/DIV
ILOAD
2A/DIV
CITH = 220pF
RITH = 34.8k
RLOAD = 1.5Ω
400µs/DIV
3772B TA03c
VIN = 5V
20µs/DIV
VOUT = 2.5V
ILOAD = 15OmA TO 2A
3772B TA03d
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LTC3772B
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TYPICAL APPLICATIO S
550kHz Micropower 5VIN to 1.8VOUT at 8A DC/DC Converter
470pF
15k
ITH/RUN
VIN
CIN
22µF
LTC3772B
GND
140k
VIN
PGATE
IPRG
VFB
Si9433DBY
×2
L1 1µH
SW
CSHD10-45L
22pF
174k
VIN
5V
COUT
100µF
×2
VOUT
1.8V
8A
3772B TA04a
L1: TOKO FDV0630-1R0
CIN: MURATA GRM32ER61C226K
COUT: MURATA GRM32ER60J107K
Efficiency vs Load Current
100
EFFICIENCY (%)
90
80
70
60
50
40
100
1000
LOAD CURRENT (mA)
10000
3772B TA04b
Start-Up
Load Step
VOUT
1V/DIV
VOUT
200mV/DIV
AC COUPLED
ITH/RUN
1V/DIV
IL
10A/DIV
IL
5A/DIV
ILOAD
10A/DIV
VIN = 5V
VOUT = 1.8V
RLOAD = 0.25Ω
500µs/DIV
3772B TA04c
VIN = 5V
20µs/DIV
VOUT = 1.8V
ILOAD = 800mA TO 8A
3772B TA04d
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LTC3772B
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PACKAGE DESCRIPTIO
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702)
0.61 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
R = 0.115
TYP
5
R = 0.05
TYP
0.40 ± 0.10
8
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.20 ±0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
2.00 ±0.10
(2 SIDES)
0.56 ± 0.05
(2 SIDES)
0.75 ±0.05
0 – 0.05
4
0.25 ± 0.05
1
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
(DDB8) DFN 0905 REV B
0.50 BSC
2.15 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) 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
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LTC3772B
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PACKAGE DESCRIPTIO
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
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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.
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LTC3772B
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TYPICAL APPLICATIO
220pF
15k
VIN
ITH/RUN
CIN
22µF
LTC3772B
GND
82.5k
PGATE
IPRG
VFB
FDC638P
L1 3.3µH
SW
B220A
22pF
VIN
3V TO 8V
COUT
47µF
VOUT
2.5V
2A
174k
3772B F05
L1: TOKO D53LC #A915AY-3R3M
CIN: TAIYO YUDEN LMK316BJ226ML
COUT: TAIYO YUDEN JMK325BJ476MM
Figure 5. 550kHz Micropower Step-Down DC/DC Converter
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Linear Technology Corporation
LT 0606 REV A • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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© LINEAR TECHNOLOGY CORPORATION 2005