LT3463/LT3463A
U
U
U
PI FU CTIO S
SHDN1 (Pin 9): Shutdown Pin for Switcher 1. Pull this pin
above 1.5V to enable Switcher 1. Pull below 0.3V to turn
it off. Do not leave this pin floating.
GND (Pin 11): Exposed Pad. Solder this exposed pad
directly to the local ground plane. This pad must be
electrically connected for proper operation.
FB1 (Pin 10): Feedback Pin for Switcher 1. Set the output
voltage by selecting values for R1 and R2.
W
BLOCK DIAGRA
V
V
OUT2
OUT1
C4
L2
D3
L1
V
IN
V
IN
C2
C3
C1
3
2
1
5
4
V
V
D2
D2
SW1
SW2
OUT1
D1
IN
9
8
7
6
SHDN1
V
SHDN1
SHDN2
SHDN2
V
300ns
300ns
REF
Q1
Q2
1.25V
OUT1
ONE-SHOT
ONE-SHOT
R3
R2
FB2
FB1
10
+
+
+
–
–
+
R1
R4
R
R
S2
S1
1.25V
25mV
25mV
–
–
A1
A2
A4
A3
V
OUT2
SWITCHER 1
SWITCHER 2
GND
11
3463 F01
LT3463: R = R = 0.1Ω
S1 S2
LT3463A: R = 0.1Ω, R = 0.063Ω
S1 S2
Figure 1. Block Diagram
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OPERATIO
The LT3463 uses a constant off-time control scheme to
provide high efficiency over a wide range of output cur-
rent. Operation can be best understood by referring to the
block diagram in Figure 1. When the voltage at the FB1 pin
is slightly above 1.25V, comparator A1 disables most of
the internal circuitry. Output current is then provided by
capacitor C2, which slowly discharges until the voltage at
the FB1 pin goes below the hysteresis point of A1 (typical
hysteresis at the FB1 pin is 8mV). A1 then enables the
internal circuitry, turns on power switch Q1, and the
current in inductor L1 begins ramping up. Once the switch
current reaches 250mA, comparator A2 resets the one-
shot, which turns off Q1 for 300ns. Q1 turns on again and
the inductor currents ramp back up to 250mA, then A2
againresetstheone-shot. Thisswitchingactioncontinues
until the output voltage is charged up (until the FB1 pin
reaches 1.25V), then A1 turns off the internal circuitry and
the cycle repeats. The second switching regulator is an
inverting converter (which generates a negative output)
but the basic operation is the same.
3463f
4
Linear Systems [ Linear Systems ]
