LTC1625 Datasheet, PDF (1/24 Pages) Linear Technology – No RSENSE TM Current Mode Synchronous Step-Down Switching Regulator

LTC1625
No R_SENSE^TM Current Mode
Synchronous Step-Down
Switching Regulator
FEATURES
s _{Highest Efficiency Current Mode Controller}
s _{No Sense Resistor Required}
s _{Stable High Current Operation}
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Wide VIN Range: 3.7V to 36V}
s _{Wide VOUT Range: 1.19V to VIN}
s _{±1% 1.19V Reference}
s _{Programmable Fixed Frequency with Injection Lock}
s _{Very Low Drop Out Operation: 99% Duty Cycle}
s _{Forced Continuous Mode Control Pin}
s _{Optional Programmable Soft Start}
s _{Pin Selectable Output Voltage}
s _{Foldback Current Limit}
s _{Output Overvoltage Protection}
s _{Logic Controlled Micropower Shutdown: IQ < 30µA}
s _{Available in 16-Lead Narrow SSOP and SO Packages}
U
APPLICATIONS
s _{Notebook and Palmtop Computers, PDAs}
s _{Cellular Telephones and Wireless Modems}
s _{Battery Chargers}
s _{Distributed Power}
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.
TYPICAL APPLICATION
C_SS
0.1µF
R_C
10k
C_C
2.2nF
SYNC
V_IN
RUN/SS TK
TG
LTC1625
I_TH
SW
BOOST
V_PROG INTV_CC
SGND
BG
V_OSENSE PGND
+
C_B 0.22µF
D_B
CMDSH-3
+
C_VCC 4.7µF
M1
Si4410DY _L1
10µH
D1
MBRS140T3
M2
Si4410DY
C_IN
10µF
V_IN
5V TO
28V
30V
×2
V_OUT
3.3V
+ ^COUT 4.5A
100µF
10V
×3
1625 F01
Figure 1. High Efficiency Step-Down Converter
Efficiency vs Load Current
100
V_IN = 10V
V_OUT = 5V
90
V_OUT = 3.3V
80
70
60
0.01
0.1
1
LOAD CURRENT (A)
10
1625 TA01
1