1
LTC1736
5-Bit Adjustable
High Efficiency Synchronous
Step-Down Switching Regulator
Figure 1. High Efficiency Step-Down Converter
■
Dual N-Channel MOSFET Synchronous Drive
■
Synchronizable/Programmable Fixed Frequency
■
Wide V
IN
Range: 3.5V to 36V Operation
■
5-Bit Digital-to-Analog V
OUT
Selection:
0.925V to 2.00V Range with 50mV/25mV Steps
■
OPTI-LOOP
TM
Compensation Minimizes C
OUT
■
±
1% Output Voltage Accuracy
■
Power Good Output Voltage Monitor
■
Active Voltage Positioning Compatible
■
Output Overvoltage Crowbar Protection
■
Internal Current Foldback
■
Latched Short-Circuit Shutdown Timer
with Defeat Option
■
Forced Continuous Control Pin
■
Optional Programmable Soft-Start
■
Remote Output Voltage Sense
■
Available in 24-Lead SSOP Package
■
Notebook and Palmtop Computers, PDAs
■
Power Supply for Mobile Pentium
®
II and
Pentium III Processors
■
Low Voltage Power Supplies
The LTC
®
1736 is a synchronous step-down switching
regulator controller optimized for CPU power. The output
voltage is programmed by a 5-bit digital-to-analog con-
verter (DAC) that adjusts the output voltage from 0.925V
to 2.00V according to Intel mobile VID specifications. The
0.8V reference is compatible with future microprocessor
generations.
The operating frequency (synchronizable up to 500kHz) is
set by an external capacitor allowing maximum flexibility
in optimizing efficiency. The output voltage is monitored by
a power good window comparator that indicates when the
output is within 7.5% of its programmed value.
Protection features include: internal foldback current lim-
iting, output overvoltage crowbar and optional short-cir-
cuit shutdown. Soft-start is provided by an external capaci-
tor that can be used to properly sequence supplies. The
operating current level is user-programmable via an exter-
nal current sense resistor. Wide input supply range allows
operation from 3.5V to 30V (36V maximum).
Pin defeatable Burst Mode
TM
operation provides high effi-
ciency at low load currents. OPTI-LOOP compensation
allows the transient response to be optimized over a wide
range of output capacitance and ESR values.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
V
OSENSE
I
TH
47pF
C
C1
330pF
C
B
0.22
µ
F
D
B
CMDSH-3
V
IN
5V TO 24V
C
OSC
47pF
RUN/SS
PGND
BG
1000pF
BOOST
SW
VIDV
CC
INTV
CC
4.7
µ
F
M2
FDS6680A
×
2
M1
FDS6680A
C
OUT
: PANASONIC EEFUEOG181R
C
IN
: MARCON THCR70EIH226ZT
L1: PANASONIC ETQP6RZIR20HFA
R
SENSE
: IRC LRF2010-01-R004J
D1
MBRS340T3
1736 F01
C
SS
0.1
µ
F
C
C2
47pF
C
OSC
R
C
33k
R
SENSE
0.004
Ω
PGOOD
VID4
VID3
VID2
VID1
VID0
SGND
SENSE
–
LTC1736
SENSE
+
TG
V
IN
+
C
OUT
180
µ
F/4V
×
4
C
IN
22
µ
F/50V
×
2
CERAMIC
V
OUT
1.35V TO 1.60V
12A
+
L1
1.2
µ
H
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
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