LTC1142/LTC1142L/LTC1142HV
Dual High Efficiency
Synchronous Step-Down
Switching Regulators
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DESCRIPTIO
FEATURES
The LTC®1142/LTC1142L/LTC1142HV are dual synchro-
nous step-down switching regulator controllers featuring
automatic Burst ModeTM operation to maintain high efficien-
cies at low output currents. The devices are composed of two
separate regulator blocks, each driving a pair of external
complementary power MOSFETs, at switching frequencies
up to 250kHz, using a constant off-time current mode archi-
tecture providing constant ripple current in the inductor.
■
Dual Outputs: 3.3V and 5V or User Programmable
■
Ultrahigh Efficiency: Over 95% Possible
■
Current Mode Operation for Excellent Line and Load
Transient Response
■
High Efficiency Maintained over 3 Decades of
Output Current
■
Low Standby Current at Light Loads: 160µA/Output
■
Independent Micropower Shutdown: IQ < 40µA
■
Wide VIN Range: 3.5V to 20V
The operating current level for both regulators is user pro-
grammableviaanexternalcurrentsenseresistor. Wideinput
supply range allows operation from 3.5V* to 18V (20V
maximum).Constantoff-timearchitectureprovideslowdrop-
out regulation limited only by the RDS(ON) of the external
MOSFET and resistance of the inductor and current sense
resistor.
■
Very Low Dropout Operation: 100% Duty Cycle
■
Synchronous FET Switching for High Efficiency
■
Available in Standard 28-Pin SSOP
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APPLICATIO S
■
Notebook and Palmtop Computers
The LTC1142 series is ideal for applications requiring dual
output voltages with high conversion efficiencies over a wide
load current range in a small amount of board space.
■
Battery-Operated Digital Devices
■
Portable Instruments
DC Power Distribution Systems
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATIO
V
IN
5.2V TO 18V
C
IN5
C
+
+
IN3
22µF
25V
× 2
22µF
25V
× 2
0.22µF
0.22µF
0V = NORMAL
>1.5V = SHDN
2
24
16
10
P-CH
P-CH
Si9430DY
Si9430DY
V
SHDN3
V
IN5
SHDN5
IN3
23
1
9
L2
L1
50µH
R
R
SENSE5
0.05Ω
SENSE3
PDRIVE 3
PDRIVE 5
50µH
V
0.05Ω
OUT3
3.3V/2A
V
OUT5
5V/2A
15
+
+
SENSE
SENSE
3
SENSE
SENSE
5
5
LTC1142HV
1000pF
1000pF
–
–
3
14
20
28
6
D1
MBRS130L
D2
NDRIVE 3
NDRIVE 5
MBRS130L
N-CH
Si9410DY
N-CH
Si9410DY
C
PGND3 SGND3
C
I
I
SGND5
17
PGND5
18
T5
T3
TH3
27
TH5
13
R
C5
1k
C
OUT5
C
+
+
OUT3
220µF
4
3
25
11
220µF
10V
× 2
10V
× 2
R
C3
1k
R
R
: DALE WSL-2010-.05
SENSE3, SENSE5
L1, L2: COILTRONICS CTX50-2-MP
PINS 5, 7, 8, 19, 21, 22: NC
C
C
C
C
T5
T3
C3
C5
560pF 3300pF 3300pF 390pF
1142 F01
NOTE: COMPONENTS OPTIMIZED FOR HIGHEST EFFICIENCY, NOT MINIMUM BOARD SPACE.
Figure 1. High Efficiency Dual 3.3V, 5V Supply
1