Datasheet

7
LTC1702
1702fa
TEST CIRCUIT
Test Circuit 1
controllers allow, improving stability and maximizing tran-
sient response. The 800mV internal reference allows
regulated output voltages as low as 800mV without exter-
nal level shifting amplifiers.
The LTC1702’s synchronous switching logic transitions
automatically into Burst Mode operation, maximizing effi-
ciency with light loads. Onboard power-good and over-
voltage (OV) fault flags indicate when the output is in
regulation or an OV fault has occurred. The OV flag can be
set to latch the device off when an OV fault has occurred,
or to automatically resume operation when the fault is
removed.
The LTC1702 takes a low input voltage and generates two
lower output voltages at very high currents. Its strengths
are small size, unmatched regulation and transient
response and high efficiency. This combination makes it
ideal for providing multiple low voltage logic supplies to
microprocessors or high density ASICs in systems using
a “2-step” regulation architecture, used in portable and
advanced desktop computers.
OVERVIEW
The LTC1702 is a dual, step-down (buck), voltage mode
feedback switching regulator controller. It is designed to
be used in a synchronous switching architecture with two
external N-channel MOSFETs per channel. It is intended to
operate from a low voltage input supply (7V maximum)
and provide a high power, high efficiency, precisely regu-
lated output voltage. Several features make it particularly
suited for microprocessor supply regulation. Output regu-
lation is extremely tight, with DC line and load regulation
and initial accuracy better than 1%, and total regulation
including transient response inside of 3% with a properly
designed circuit. The 550kHz switching frequency allows
the use of physically small, low value external components
without compromising performance.
The LTC1702’s internal feedback amplifier is a 25MHz
gain-bandwidth op amp, allowing the use of complex
multipole/zero compensation networks. This allows the
feedback loop to maintain acceptable phase margin at
higher frequencies than traditional switching regulator
APPLICATIONS INFORMATION
WUU
U
V
CC
5V
5V
10k
2k
C
L
C
L
C
L
C
L
BOOST1
TG1
BG1
SW1
I
MAX1
FCB
PGOOD1
RUN/SS1
COMP1
FB1
LTC1702
BOOST2
TG2
BG2
SW2
I
MAX2
PGOOD2
FAULT
RUN/SS2
COMP2
FB2
0.1µF
100µF
V
PGOOD1
V
FB1
V
FB2
V
PGOOD2
V
FAULT
I
BOOST1
I
CC
I
PVCC
I
BOOST2
f
OSC
MEASURED
1702 TC
PV
CC
GND PGND
+
2k
5V
10k