LTC1735-1_15 Datasheet, PDF (1/28 Pages) Linear Technology – High Efficiency Synchronous Step-Down Switching Regulator

FEATURES
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Programmable/Synchronizable Fixed Frequency}
s _{VOUT Range: 0.8V to 7V}
s _{Wide VIN Range: 3.5V to 36V Operation}
s _{Very Low Dropout Operation: 99% Duty Cycle}
s _OPTI-LOOP^TM _{Compensation Minimizes COUT}
s _{±1% Output Voltage Accuracy}
s _{Power Good Output Voltage Monitor}
s _{Internal Current Foldback}
s _{Output Overvoltage Crowbar Protection}
s _{Latched Short-Circuit Shutdown Timer}
with Defeat Option
s _{Optional Programmable Soft-Start}
s _{Remote Output Voltage Sense}
s _{Logic Controlled Micropower Shutdown: IQ < 25µA}
s _{Available in 16-Lead Narrow SSOP and SO Packages}
U
APPLICATIO S
s _{Notebook and Palmtop Computers, PDAs}
s _{Power Supply for Mobile Pentium}^® _{III Processor with}
SpeedStep^TM Technology
s _{Cellular Telephones and Wireless Modems}
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation. SpeedStep is a trademark of Intel
Corporation.
LTC1735-1
High Efficiency
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
The LTC^®1735-1 is a synchronous step-down switching
regulator controller optimized for CPU power. OPTI-LOOP
compensation allows the transient response to be opti-
mized over a wide range of output capacitance and ESR
values.
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, con-
forming to Intel Mobile CPU Specifications.
Protection features include internal foldback current lim-
iting, output overvoltage crowbar and optional short-
circuit shutdown. Soft-start is provided by an external
capacitor that can be used to properly sequence supplies.
The operating current level is user-programmable via an
external current sense resistor. Wide input supply range
allows operation from 3.5V to 30V (36V maximum).
Pin defeatable Burst Mode^TM operation provides high
efficiency at low load currents while 99% duty cycle
provides low dropout operation.
TYPICAL APPLICATIO
PGOOD
V_IN
4.5V TO 24V
C_OSC 47pF
C_C2 330pF
47pF
1
16
C_OSC
TG
C_SS 0.1µF
R_C1 33k
2
RUN/SS
15
BOOST
3
14
I_TH LTC1735-1 SW
C_C1 47pF
4
PGOOD
13
V_IN
5 _{SENSE –}
1000pF _{6 SENSE +}
12
INTV_CC
11
BG
C_B 0.22µF
D1
CMDSH-3
+
4.7µF
7
V_OSENSE
PGND ¹⁰
8
SGND
9
EXTV_CC
5V
(OPTIONAL)
10Ω
10Ω
Q1
FDS6680A
L1
1.2µH
D2
MBRS340T3
Q2, Q3
FDS6680A
×2
C_IN
22µF
50V
CERAMIC
×2
R_SENSE
0.004Ω
47pF
47pF
R2
14.3k
0.5%
C_IN: MARCON THCR70E1H226ZT
C_OUT: PANASONIC EEFUE06181R
L1: PANASONIC ETQP6RZ1R20HFA
R_SENSE: IRC CRF2010-01-R004J
R1
10k
0.5% ₊
R3
33.2k
1%
Q4
2N7002
V_OUT
1.35V TO 1.60V
12A
C_OUT
180µF
4V
PANASONIC SP
×4
V_SEL = 1: V_OUT = 1.60V
V_SEL = 0: V_OUT = 1.35V
GND
1735-1 F01
Figure 1. CPU Core DC/DC Converter with Dynamic Voltage Selection from SpeedStep Enabled Processors
1