Datasheet LTC1622 (Analog Devices) - 5
| Hersteller | Analog Devices |
| Beschreibung | Low Input Voltage Current Mode Step-Down DC/DC Controller |
| Seiten / Seite | 16 / 5 — FUNCTIONAL DIAGRA. OPERATIO. (Refer to Functional Diagram). Main Control … |
| Dateiformat / Größe | PDF / 198 Kb |
| Dokumentensprache | Englisch |
FUNCTIONAL DIAGRA. OPERATIO. (Refer to Functional Diagram). Main Control Loop. Burst Mode Operation
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LTC1622
U U W FUNCTIONAL DIAGRA
VIN VCC Y = “0” ONLY WHEN X IS A CONSTANT “1” BURST DEFEAT OTHERWISE Y = “1” Y 1µA X SLOPE SYNC/ COMP 5 MODE OSC 0.36V 0.3V – V 3 + SENSE– 1 8 V FB IN – EN FREQ + SHIFT – SLEEP 0.8V + VIN VREF EA 0.12V + + – ICOMP – Ω BURST 2.5µA gm = 0.5m VIN SWITCHING 0.8V 2 S LOGIC REFERENCE RUN/ RUN/SS 4 I AND TH SOFT-START R Q V V BLANKING IN REF 0.8V CIRCUIT R PDRV S1 7 UVLO + TRIP = 1.97V OV 6 VREF + 0.12V – GND SHUTDOWN 1622 BD
U OPERATIO (Refer to Functional Diagram) Main Control Loop
current source to charge up the soft-start capacitor CSS. When C The LTC1622 is a constant frequency current mode switch- SS reaches 0.7V, the main control loop is enabled with the I ing regulator. During normal operation, the external TH voltage clamped at approximately 5% of its maximum value. As C P-channel power MOSFET is turned on each cycle when SS continues to charge, ITH is gradu- ally released allowing normal operation to resume. the oscillator sets the RS latch (RS1) and turned off when the current comparator (ICOMP) resets the latch. The peak Comparator OV guards against transient overshoots inductor current at which ICOMP resets the RS latch is > 16% by turning off the P-channel power MOSFET and controlled by the voltage on the ITH pin, which is the output keeping it off until the fault is removed. of the error amplifier EA. An external resistive divider connected between V
Burst Mode Operation
OUT and ground allows EA to receive an output feedback voltage VFB. When the load current The LTC1622 can be enabled to go into Burst Mode increases, it causes a slight decrease in VFB relative to the operation at low load currents simply by leaving the SYNC/ 0.8V reference, which in turn causes the ITH voltage to MODE pin open or connecting it to a voltage of at least 2V. increase until the average inductor current matches the In this mode, the peak current of the inductor is set as if new load current. VITH = 0.36V (at low duty cycles) even though the voltage The main control loop is shut down by pulling the RUN/SS at the ITH pin is at lower value. If the inductor’s average pin low. Releasing RUN/SS allows an internal 2.5µA current is greater than the load requirement, the voltage at 5
U U W FUNCTIONAL DIAGRA
VIN VCC Y = “0” ONLY WHEN X IS A CONSTANT “1” BURST DEFEAT OTHERWISE Y = “1” Y 1µA X SLOPE SYNC/ COMP 5 MODE OSC 0.36V 0.3V – V 3 + SENSE– 1 8 V FB IN – EN FREQ + SHIFT – SLEEP 0.8V + VIN VREF EA 0.12V + + – ICOMP – Ω BURST 2.5µA gm = 0.5m VIN SWITCHING 0.8V 2 S LOGIC REFERENCE RUN/ RUN/SS 4 I AND TH SOFT-START R Q V V BLANKING IN REF 0.8V CIRCUIT R PDRV S1 7 UVLO + TRIP = 1.97V OV 6 VREF + 0.12V – GND SHUTDOWN 1622 BD
U OPERATIO (Refer to Functional Diagram) Main Control Loop
current source to charge up the soft-start capacitor CSS. When C The LTC1622 is a constant frequency current mode switch- SS reaches 0.7V, the main control loop is enabled with the I ing regulator. During normal operation, the external TH voltage clamped at approximately 5% of its maximum value. As C P-channel power MOSFET is turned on each cycle when SS continues to charge, ITH is gradu- ally released allowing normal operation to resume. the oscillator sets the RS latch (RS1) and turned off when the current comparator (ICOMP) resets the latch. The peak Comparator OV guards against transient overshoots inductor current at which ICOMP resets the RS latch is > 16% by turning off the P-channel power MOSFET and controlled by the voltage on the ITH pin, which is the output keeping it off until the fault is removed. of the error amplifier EA. An external resistive divider connected between V
Burst Mode Operation
OUT and ground allows EA to receive an output feedback voltage VFB. When the load current The LTC1622 can be enabled to go into Burst Mode increases, it causes a slight decrease in VFB relative to the operation at low load currents simply by leaving the SYNC/ 0.8V reference, which in turn causes the ITH voltage to MODE pin open or connecting it to a voltage of at least 2V. increase until the average inductor current matches the In this mode, the peak current of the inductor is set as if new load current. VITH = 0.36V (at low duty cycles) even though the voltage The main control loop is shut down by pulling the RUN/SS at the ITH pin is at lower value. If the inductor’s average pin low. Releasing RUN/SS allows an internal 2.5µA current is greater than the load requirement, the voltage at 5