LTC1439_15 Datasheet, PDF (1/32 Pages) Linear Technology – Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators

LTC1438/LTC1439
FEATURES
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
DESCRIPTIO
■ _{Maintains Constant Frequency at Low Output}
Currents
■ _{Dual N-Channel MOSFET Synchronous Drive}
■ _{Programmable Fixed Frequency (PLL Lockable)}
■ _{Wide VIN Range: 3.5V to 36V Operation}
■ _{Ultrahigh Efficiency}
■ _{Very Low Dropout Operation: 99% Duty Cycle}
■ _{Low Dropout, 0.5A Linear Regulator for VPP}
Generation or Low Noise Audio Supply
■ _{Built-In Power-On Reset Timer}
■ _{Programmable Soft Start}
■ _{Low-Battery Detector}
■ _{Remote Output Voltage Sense}
■ _{Foldback Current Limiting (Optional)}
■ _{Pin Selectable Output Voltage}
■ _{Logic-Controlled Micropower Shutdown: IQ < 30µA}
■ _{Output Voltages from 1.19V to 9V}
■ _{Available in 28- and 36-Lead SSOP Packages}
U
APPLICATIO S
■ _{Notebook and Palmtop Computers, PDAs}
■ _{Portable Instruments}
■ _{Battery-Operated Devices}
■ _{DC Power Distribution Systems}
The LTC ^®1438/LTC1439 are dual, synchronous step-
down switching regulator controllers which drive external
N-channel power MOSFETs in a phase-lockable fixed
frequency architecture. The Adaptive Power^TM output stage
selectively drives two N-channel MOSFETs at frequencies
up to 400kHz while reducing switching losses to maintain
high efficiencies at low output currents.
An auxiliary 0.5A linear regulator using an external PNP
pass device provides a low noise, low dropout voltage
source. A secondary winding feedback control pin (SFB1)
guarantees regulation regardless of load on the main
output by forcing continuous operation.
An additional comparator is available for use as a low
battery detector. A power-on reset timer (POR) is included
which generates a signal delayed by 65536/f_CLK (typ
300ms) after the output is within 5% of the regulated
output voltage. Internal resistive dividers provide pin
selectable output voltages with remote sense capability on
one of the two outputs.
The operating current levels are user-programmable via
external current sense resistors. Wide input supply range
allows operation from 3.5V to 30V (36V maximum).
, LTC and LT are registered trademarks of Linear Technology Corporation. Adaptive
Power is a trademark of Linear Technology Corporation. All other trademarks are the prop-
erty of their respective owners. Protected by U.S. Patents including 5481178, 6304066,
5929620, 6580258, 5705919, 5731731.
TYPICAL APPLICATIO
D_B1, CMDSH-3
D_B2, CMDSH-3 + _4.7µF
16V
BOOST 1
V_PROG1
V_IN
INTV_CC BOOST 2
M1
TGL1
TGL2
L1
10µH
D1
MBR140T3
V_OUT1
5V
3.5A
R_SENSE1
0.03Ω
+ C_OUT1
220µF
10V
M3*
C_B1
0.1µF
M2
1000pF
C_C1
1000pF
C_C1A
220pF
TGS1
SW1
BG1
SENSE⁺ 1
LTC1439
SENSE^– 1
I_TH1
RUN/SS1
C_OSC V_PROG2
R_C1
C_SS1
C_OSC
10k
0.1µF
56pF
SGND
TGS2
SW2
BG2
SENSE⁺ 2
SENSE^– 2
V_OSENSE2
I_TH2
PGND RUN/SS2
C_SS2
0.1µF
M6*
C_B2, 0.1µF
M5
1000pF
C_C2
1000pF
R_C2
C_C2A
10k
470pF
M1, M2, M4, M5: Si4412ADY M3, M6: IRLML2803 *NOT REQUIRED FOR LTC1438 BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
+
M4
L2
10µH
C_IN
22µF
35V
×4
V_IN
5.2V TO 28V
D2
MBR140T3
R_SENSE2
0.03Ω
+
1438 F01
V_OUT2
3.3V
3.5A
C_OUT
220µF
10V
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