LT3463 Ver la hoja de datos (PDF) - Linear Technology
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LT3463 Datasheet PDF : 8 Pages
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LT3463/LT3463A
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.
FB1 (Pin 10): Feedback Pin for Switcher 1. Set the output
voltage by selecting values for R1 and R2.
GND (Pin 11): Exposed Pad. Solder this exposed pad
directly to the local ground plane. This pad must be
electrically connected for proper operation.
BLOCK DIAGRA
L1
VIN
C1
VOUT1
VOUT2 D3
C4
C2
C3
L2
VIN
3
VIN
SHDN1 9 SHDN1
2
SW1
1
VOUT1
D1
5
4
D2 SW2
D2
SHDN2 8 SHDN2
VOUT1
R2
FB1
10
–
R1
1.25V +
300ns
ONE-SHOT
A1
A2
SWITCHER 1
LT3463: RS1 = RS2 = 0.1Ω
LT3463A: RS1 = 0.1Ω, RS2 = 0.063Ω
Q1
Q2
RS1
25mV
RS2
25mV
GND
11
Figure 1. Block Diagram
300ns
ONE-SHOT
VREF
1.25V
7
A4
A3
SWITCHER 2
R3
FB2
6
R4
VOUT2
3463 F01
U
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
again resets the one-shot. This switching action continues
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
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