LTC1625
No R
SENSE
TM
Current Mode
Synchronous Step-Down
Switching Regulator
FEATURES
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DESCRIPTION
The LTC
®
1625 is a synchronous step-down switching
regulator controller that drives external N-Channel power
MOSFETs using few external components. Current mode
control with MOSFET V
DS
sensing eliminates the need for
a sense resistor and improves efficiency. The frequency of
a nominal 150kHz internal oscillator can be synchronized
to an external clock over a 1.5:1 frequency range.
Burst Mode
TM
operation at low load currents reduces
switching losses and low dropout operation extends oper-
ating time in battery-powered systems. A forced continu-
ous mode control pin can assist secondary winding
regulation by disabling Burst Mode operation when the
main output is lightly loaded.
Fault protection is provided by foldback current limiting
and an output overvoltage comparator. An external ca-
pacitor attached to the RUN/SS pin provides soft start
capability for supply sequencing. A wide supply range
allows operation from 3.7V (3.9V for LTC1625I) to 36V at
the input and 1.19V to V
IN
at the output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R
SENSE
and Burst Mode are trademarks of Linear Technology Corporation.
Highest Efficiency Current Mode Controller
No Sense Resistor Required
Stable High Current Operation
Dual N-Channel MOSFET Synchronous Drive
Wide V
IN
Range: 3.7V to 36V
Wide V
OUT
Range: 1.19V to V
IN
±1%
1.19V Reference
Programmable Fixed Frequency with Injection Lock
Very Low Drop Out Operation: 99% Duty Cycle
Forced Continuous Mode Control Pin
Optional Programmable Soft Start
Pin Selectable Output Voltage
Foldback Current Limit
Output Overvoltage Protection
Logic Controlled Micropower Shutdown: I
Q
< 30µA
Available in 16-Lead Narrow SSOP and SO Packages
APPLICATIONS
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Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Battery Chargers
Distributed Power
TYPICAL APPLICATION
Efficiency vs Load Current
SYNC
C
SS
0.1µF
RUN/SS
LTC1625
I
TH
R
C
10k
C
C
2.2nF
SW
BOOST
V
PROG
INTV
CC
SGND
BG
D
B
CMDSH-3
C
B
0.22µF
C
VCC
4.7µF
D1
MBRS140T3
M2
Si4410DY
V
IN
TK
TG
M1
Si4410DY
L1
10µH
C
IN
10µF
30V
×
2
V
IN
5V TO
28V
100
V
IN
= 10V
V
OUT
= 5V
+
+
+
V
OUT
3.3V
C
OUT
4.5A
100µF
10V
×
3
EFFICIENCY (%)
V
OSENSE
PGND
1625 F01
Figure 1. High Efficiency Step-Down Converter
U
U
U
90
V
OUT
= 3.3V
80
70
60
0.01
0.1
1
LOAD CURRENT (A)
10
1625 TA01
1
LINER [ LINEAR TECHNOLOGY ]
