Datasheet LT1615, LT1615-1 (Analog Devices) - 4
| Manufacturer | Analog Devices |
| Description | Micropower Step-Up DC/DC Converters in ThinSOT |
| Pages / Page | 8 / 4 — BLOCK DIAGRA. Figure 1. LT1615 Block Diagram. OPERATIO |
| File Format / Size | PDF / 168 Kb |
| Document Language | English |
BLOCK DIAGRA. Figure 1. LT1615 Block Diagram. OPERATIO
Model Line for this Datasheet
Text Version of Document
LT1615/LT1615-1
W BLOCK DIAGRA
D1 L1 V V IN OUT C1 V C2 IN SHDN SW 5 4 1 R5 R6 40k 40k A1 + ENABLE VOUT – R1 (EXTERNAL) FB Q1 Q2 400ns 3 Q3 X10 ONE-SHOT R2 DRIVER (EXTERNAL) R3 RESET 30k + R4 0.12Ω 140k – 42mV* A2 GND 2 1615/-1 BD * 12mV FOR LT1615-1
Figure 1. LT1615 Block Diagram U OPERATIO
The LT1615 uses a constant off-time control scheme to current ramps back up to 350mA, then A2 resets the one- provide high efficiencies over a wide range of output shot, again allowing L1 to deliver current to the output. current. Operation can be best understood by referring to This switching action continues until the output voltage is the block diagram in Figure 1. Q1 and Q2 along with R3 and charged up (until the FB pin reaches 1.23V), then A1 turns R4 form a bandgap reference used to regulate the output off the internal circuitry and the cycle repeats. The LT1615 voltage. When the voltage at the FB pin is slightly above contains additional circuitry to provide protection during 1.23V, comparator A1 disables most of the internal cir- start-up and under short-circuit conditions. When the FB cuitry. Output current is then provided by capacitor C2, pin voltage is less than approximately 600mV, the switch which slowly discharges until the voltage at the FB pin off-time is increased to 1.5µs and the current limit is drops below the lower hysteresis point of A1 (typical reduced to around 250mA (70% of its normal value). This hysteresis at the FB pin is 8mV). A1 then enables the reduces the average inductor current and helps minimize internal circuitry, turns on power switch Q3, and the the power dissipation in the LT1615 power switch and in current in inductor L1 begins ramping up. Once the switch the external inductor and diode. The LT1615-1 operates in current reaches 350mA, comparator A2 resets the one- the same manner, except the switch current is limited to shot, which turns off Q3 for 400ns. L1 then delivers 100mA (the A2 reference voltage is 12mV instead of current to the output through diode D1 as the inductor 42mV). current ramps down. Q3 turns on again and the inductor sn16151 16151fas 4
W BLOCK DIAGRA
D1 L1 V V IN OUT C1 V C2 IN SHDN SW 5 4 1 R5 R6 40k 40k A1 + ENABLE VOUT – R1 (EXTERNAL) FB Q1 Q2 400ns 3 Q3 X10 ONE-SHOT R2 DRIVER (EXTERNAL) R3 RESET 30k + R4 0.12Ω 140k – 42mV* A2 GND 2 1615/-1 BD * 12mV FOR LT1615-1
Figure 1. LT1615 Block Diagram U OPERATIO
The LT1615 uses a constant off-time control scheme to current ramps back up to 350mA, then A2 resets the one- provide high efficiencies over a wide range of output shot, again allowing L1 to deliver current to the output. current. Operation can be best understood by referring to This switching action continues until the output voltage is the block diagram in Figure 1. Q1 and Q2 along with R3 and charged up (until the FB pin reaches 1.23V), then A1 turns R4 form a bandgap reference used to regulate the output off the internal circuitry and the cycle repeats. The LT1615 voltage. When the voltage at the FB pin is slightly above contains additional circuitry to provide protection during 1.23V, comparator A1 disables most of the internal cir- start-up and under short-circuit conditions. When the FB cuitry. Output current is then provided by capacitor C2, pin voltage is less than approximately 600mV, the switch which slowly discharges until the voltage at the FB pin off-time is increased to 1.5µs and the current limit is drops below the lower hysteresis point of A1 (typical reduced to around 250mA (70% of its normal value). This hysteresis at the FB pin is 8mV). A1 then enables the reduces the average inductor current and helps minimize internal circuitry, turns on power switch Q3, and the the power dissipation in the LT1615 power switch and in current in inductor L1 begins ramping up. Once the switch the external inductor and diode. The LT1615-1 operates in current reaches 350mA, comparator A2 resets the one- the same manner, except the switch current is limited to shot, which turns off Q3 for 400ns. L1 then delivers 100mA (the A2 reference voltage is 12mV instead of current to the output through diode D1 as the inductor 42mV). current ramps down. Q3 turns on again and the inductor sn16151 16151fas 4
