LTC1876_15 Datasheet, PDF (1/36 Pages) Linear Technology – High Efficiency, 2-Phase, Dual Synchronous Step-Down Switching Controller and Step-Up Regulator

LTC1876
High Efficiency, 2-Phase,
Dual Synchronous Step-Down Switching
Controller and Step-Up Regulator
FEATURES
Step-Down Controller
s _{Out-of-Phase Controllers Reduce Required Input}
Capacitance and Power Supply Induced Noise
s _{Power Good Output Voltage Indicator}
s _OPTI-LOOP^TM _{Compensation Minimizes COUT}
s _{DC Programmed Fixed Frequency 150kHz to 300kHz}
s _{Wide VIN Range: 3.5V to 36V Operation}
s _{Very Low Dropout Operation: 99% Duty Cycle}
s _{Adjustable Soft-Start Current Ramping}
s _{Latched Short-Circuit Shutdown with Defeat Option}
s _{Remote Output Voltage Sense and OV Protection}
s _{5V and 3.3V Standby Regulators}
s _{Selectable Const. Freq. or Burst Mode}^TM _Operation
Step-Up Regulator
s _{High Operating Switching Frequency of 1.2MHz}
s _{Low Internal VCESAT Switch: 400mV @ 1A, VIN = 3V}
s _{Wide VIN Range: 2.6V to 16V Operation}
s _{High Output VoltUage: Up to 34V}
APPLICATIO S
s _{3.3V Input Step-Down Converter}
s _{Notebook and Palmtop Computers, PDAs}
s _{Battery-Operated Digital Devices}
DESCRIPTIO
The LTC^®1876 is a high performance triple output switching
regulator. It incorporates a dual step-down switching con-
troller that drives all N-channel synchronous power MOSFET
stages. A step-up regulator with an internal 1A, 36V switch
provides the third output.
The step-down controllers minimize power loss and noise
by operating the output stage of each controller out of
phase. OPTI-LOOP compensation allows the transient
response to be optimized over a wide range of output
capacitance and ESR values. A RUN/SS pin for each
controller provides both soft-start and an optional timed,
short-circuit shutdown that can be configured to latch off
one or both controllers. Current foldback provides
additional short-circuit protection. In an overvoltage
condition, the bottom MOSFET is latched on until V_OUT
returns to normal. The FCB pin can be used to inhibit Burst
Mode operation or to enable regulation of a secondary
output voltage.
The step-up regulator operates at 1.2MHz, allowing the
use of tiny low cost capacitors and inductors. In addition,
its internal 1A switch allows high current outputs to be
generated. Its current mode control scheme provides
excellent line and load regulation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
V_IN
5.2V
TO 28V ^33µF
35V
ALUM
10µF
35V
CER
M3
6.3µH
1µF
CER
0.1µF
M4
0.01Ω
V_OUT2
3.3V
5A
+
56µF
4V
SP
63.4k
1%
1000pF
220pF
20k
1%
15k
INTV_CC AUXV_IN V_IN
TG2
TG1
BOOST2
BOOST1
SW2
SW1
LTC1876
BG2
BG1
AUXSW
PGND
AUXV_FB
PGOOD
SENSE2⁺
SENSE2^–
AUXSD
SENSE1⁺
SENSE1^–
V_OSENSE2
V_OSENSE1
I_TH2
I_TH1
RUN/SS2 SGND RUN/SS1
0.1µF
0.1µF
4.7µF
10V
M1
0.1µF
M2
10µH
10µF
20V
6.8µH
1000pF
86.6k, 1%
220pF
15k
105k
1%
10.2k 20k
1% 1%
V_OUT3
12V
200mA
0.01Ω
47µF
6.3V
SP
V_OUT1
5V
4A
M1, M2, M3, M4: FDS6680A
1876 TA01
Figure 1. High Efficiency Triple 5V/3.3V/12V Power Supply
1876fa
1