Datasheet LT3463, LT3463A (Analog Devices) - 4

LT3463/LT3463A
U U U PI FU CTIO S SHDN1 (Pin 9):
Shutdown Pin for Switcher 1. Pull this pin
GND (Pin 11):
Exposed Pad. Solder this exposed pad above 1.5V to enable Switcher 1. Pull below 0.3V to turn directly to the local ground plane. This pad must be it off. Do not leave this pin floating. 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
VOUT1 VOUT2 L1 D3 C4 L2 VIN VIN C1 C2 C3 3 2 1 5 4 VIN SW1 VOUT1 D2 SW2 D1 D2 SHDN1 9 SHDN1 SHDN2 8 SHDN2 300ns 300ns V Q1 REF V Q2 OUT1 ONE-SHOT 1.25V ONE-SHOT 7 R2 R3 FB1 FB2 10 – + + + 6 R1 R4 RS1 RS2 1.25V + – 25mV 25mV – – A1 A2 A4 A3 VOUT2 SWITCHER 1 SWITCHER 2 GND 11 LT3463: R 3463 F01 S1 = RS2 = 0.1Ω LT3463A: RS1 = 0.1Ω, RS2 = 0.063Ω
Figure 1. Block Diagram U OPERATIO
The LT3463 uses a constant off-time control scheme to current in inductor L1 begins ramping up. Once the switch provide high efficiency over a wide range of output cur- current reaches 250mA, comparator A2 resets the one- rent. Operation can be best understood by referring to the shot, which turns off Q1 for 300ns. Q1 turns on again and block diagram in Figure 1. When the voltage at the FB1 pin the inductor currents ramp back up to 250mA, then A2 is slightly above 1.25V, comparator A1 disables most of again resets the one-shot. This switching action continues the internal circuitry. Output current is then provided by until the output voltage is charged up (until the FB1 pin capacitor C2, which slowly discharges until the voltage at reaches 1.25V), then A1 turns off the internal circuitry and the FB1 pin goes below the hysteresis point of A1 (typical the cycle repeats. The second switching regulator is an hysteresis at the FB1 pin is 8mV). A1 then enables the inverting converter (which generates a negative output) internal circuitry, turns on power switch Q1, and the but the basic operation is the same. 3463f 4