LTC1438 Datasheet, PDF (1/32 Pages) Linear Technology – Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators

LTC1438/LTC1439
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
FEATURES
DESCRIPTION
s Maintains Constant Frequency at Low Output Currents The LTC ^®1438/LTC1439 are dual, synchronous step-
s Dual N-Channel MOSFET Synchronous Drive
down switching regulator controllers which drive external
s Programmable Fixed Frequency (PLL Lockable)
N-channel power MOSFETs in a phase-lockable fixed
s Wide V_IN Range: 3.5V to 36V Operation
s Ultrahigh Efficiency
frequency architecture. The Adaptive Power^TM output stage
selectively drives two N-channel MOSFETs at frequencies
s Very Low Dropout Operation: 99% Duty Cycle
up to 400kHz while reducing switching losses to maintain
s Low Dropout, 0.5A Linear Regulator for VPP
high efficiencies at low output currents.
Generation or Low Noise Audio Supply
s Built-In Power-On Reset Timer
s Programmable Soft Start
s Low-Battery Detector
s Remote Output Voltage Sense
s Foldback Current Limiting (Optional)
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.
s Pin Selectable Output Voltage
An additional comparator is available for use as a low
s Logic-Controlled Micropower Shutdown: I_Q < 30µA
s Output Voltages from 1.19V to 9V
s Available in 28- and 36-Lead SSOP Packages
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
U
APPLICATIONS
output voltage. Internal resistive dividers provide pin
selectable output voltages with remote sense capability on
one of the two outputs.
s _{Notebook and Palmtop Computers, PDAs}
s _{Portable Instruments}
s _{Battery-Operated Devices}
s _{DC Power Distribution Systems}
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.
TYPICAL APPLICATION
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_DSC 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: Si4412DY M3, M6: IRLML2803 *NOT REQUIRED FOR LTC1438 BOLD LINES INDICATE HIGH CURRENT PATHS
+
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
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
1