LT1940 Linear Technology, LT1940 Datasheet - Page 6

• Manufacturer Part Number: LT1940
• Description: Dual Monolithic 1.4A/ 1.1MHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

BLOCK DIAGRA
LT1940
The LT1940 is a dual, constant frequency, current mode
buck regulator with internal 2A power switches. The two
regulators share common circuitry including input source,
voltage reference and oscillator, but are otherwise inde-
pendent. This section describes the operation of the
LT1940; refer to the Block Diagram.
If the RUN/SS (run/soft-start) pins are both tied to ground,
the LT1940 is shut down and draws 30 A from the input
6
C
F
CLK
Figure 2. Block Diagram of the LT1940 with Associated External Components (One of Two Switching Regulators Shown)
RUN/SS2
RUN/SS1
R
C
C
GND
V
C
PG
C
RUN/SS
2 A
2 A
SLOPE
+
–
SLAVE
OSC
0.5V
W
0.9V
AND REF
INT REG
C1
V
IN
–
+
CLAMP
I
LIMIT
R
S
MASTER
OSC
Q
CLK1
CLK2
ERROR
source tied to V
external soft-start capacitors, generating voltage ramps at
these pins. If either RUN/SS pin exceeds 0.5V, the internal
bias circuits turn on, including the internal regulator,
1.25V reference and 1.1MHz master oscillator. In this
state, the LT1940 draws 3.5mA from V
both RUN/SS pins are high. Neither switching regulator
will begin to operate until its RUN/SS pin reaches ~0.8V.
AMP
–
+
+
–
125mV
1.25V
IN
. Internal 2 A current sources charge
1940 F02
BOOST
SW
V
FB
IN
R2
D1
C
IN
IN
C3
D2
L1
R1
IN
, whether one or
C1
OUT
1940i