LTC3521 Datasheet, PDF (8/20 Pages) Linear Technology – Wide VIN, 1A Buck-Boost DC/DC and Dual 600mA Buck DC/DC Converters

LTC3521
Pin Functions
NC (Pin 19, UF Package Only): No Internal Connection.
PV_IN2 (Pin 20/Pin 22): High Current Power Supply Connec-
tion Used to Supply the Buck Converter Power Switches.
This pin should be bypassed by a 10µF or larger ceramic
cap. The bypass capacitor should be placed as close to
the pin as possible and should have a short return path
to ground. Pins V_IN, PV_IN1, and PV_IN2 must be connected
together in the application circuit.
Exposed Pad (Pin 21/Pin 25): The Exposed Pad must
be electrically connected to ground. Pins GND, PGND1A,
PGND1B, PGND2 and the Exposed Pad must be connected
together in the application circuit.
PGND1A (Pin 21, UF Package Only): High Current Ground
Connection for the Buck-Boost Switch B. The PCB trace
connecting this pin to ground should be made as short
and wide as possible.
Block Diagram (UF Package)
11
PV_IN1
15
14
SW1A SW1B
A
INTERNAL
V_CC
4 ^VIN
BC
PGND1A PGND1B
16
PV_OUT
FILTER
FORWARD
+ ILIMIT 0.55V +
D
2.1A –
–
+
0.375A –
REVERSE I_LIMIT
+
0A –
I_ZERO
PGOOD1
3
PV_OUT
PWM
6
SHDN2
8
22 ^PVIN2
PV_IN2
GATE
DRIVES
BUCK-BOOST
PWM
LOGIC
OSCILLATOR
UVLO
FB1
10
0.6V
SOFT-START
RAMP
SHDN1
9
SHDN3
7
PV_IN2
SW2
19
GATE
DRIVES
BUCK
PWM
LOGIC
BUCK
PWM
LOGIC
GATE
DRIVES
SW3
17
FB2
24
PGND2
+
ZERO CROSSING
0A –
1.05A +
I_LIMIT
–
+
SLOPE
COMPENSATION
–^gm
+
0.60V ₊₊
–
ZERO CROSSING
I_LIMIT
PGND2
0A
1.05A
SLOPE
COMPENSATION
g_m
FB3
23
0.60V
SOFT-START
RAMP
PGOOD2
2
0.55V
1V
0.6V
0.9V
0.55V
BANDGAP
REFERENCE
AND OT
SHUTDOWN
GND
PGND1A PGND1B
PGND2
5
21
12
18
SOFT-START
RAMP
–
0.55V ⁺
PGOOD3
1
3521 BD

3521f