Datasheet LT3473, LT3473A (Analog Devices) - 7
| Hersteller | Analog Devices |
| Beschreibung | Micropower 1A Boost Converter with Schottky and Output Disconnect |
| Seiten / Seite | 12 / 7 — APPLICATIO S I FOR ATIO. Operation. Switching Waveforms. Transient … |
| Dateiformat / Größe | PDF / 276 Kb |
| Dokumentensprache | Englisch |
APPLICATIO S I FOR ATIO. Operation. Switching Waveforms. Transient Response. Shutdown Waveforms. Start-Up Waveforms
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LT3473/LT3473A
U U W U APPLICATIO S I FOR ATIO Operation
causes the FB voltage to decrease, VC increases causing A1 to enable the power section circuitry. The chip starts switch- The LT3473 combines a current mode, fixed frequency ing. If the load is light, the output voltage (and FB voltage) PWM architecture with Burst Mode micropower operation will increase until A1 turns off the power section. The output to maintain high efficiency at light loads. Operation can voltage starts to fall again. This cycle repeats and gener- best be understood by referring to the Block Diagram. ates low frequency ripple at the output. This Burst Mode The reference of the part is determined by the lower of the operation keeps the output regulated and reduces average internal 1.25V bandgap reference and the voltage at the current into the IC, resulting in high efficiency at light load. CTRL pin. The error amplifier compares voltage at the FB If the output load increases sufficiently, A1’s output remains pin with the reference and generates an error signal VC. high, resulting in continuous operation. When VC is below the Burst Mode threshold voltage, BTH, At the start of each oscillator cycle, the SR latch is set, the hysteretic comparator, A1, shuts off the power section turning on the power switch Q1. A voltage proportional to leaving only the low power circuitry running. Total current the switch current is added to a stabilizing ramp and the consumption in this state is minimized. As output loading
Switching Waveforms Switching Waveforms Transient Response
VOUT IL IL 200mV/DIV 200mA/DIV 200mA/DIV IL 200mA/DIV VSW VSW 10V/DIV 10V/DIV 11mA ILOAD 1mA V V 0.5 V 500µs/DIV 3473 AI03 IN = 3.6V 0.5µs/DIV 3473 AI01 IN = 3.6V µs/DIV 3473 AI02 IN = 3.6V V V V OUT = 20V OUT = 20V OUT = 20V I I LOAD = 50mA LOAD = 8mA
Transient Response Transient Response Transient Response
V V OUT VOUT OUT 500mV/DIV 500mV/DIV 500mV/DIV I I L L IL 500mA/DIV 500mA/DIV 500mA/DIV 51mA 55mA 75mA ILOAD ILOAD I 1mA LOAD 5mA 25mA VIN = 3.6V 500µs/DIV 3473 AI04 VIN = 3.6V 500µs/DIV 3473 AI05 VIN = 3.6V 200µs/DIV 3473 AI06 VOUT = 20V VOUT = 20V VOUT = 20V
Shutdown Waveforms Start-Up Waveforms
VOUT V 10V/DIV OUT 10V/DIV CAP 0.5V/DIV IL 500mA/DIV SHDN SHDN 5V/DIV 2V/DIV VIN = 3.6V 100µs/DIV 3473 AI07 VIN = 3.6V 500µs/DIV 3473 AI08 VOUT = 20V VOUT = 20V ILOAD = 60mA ILOAD = 30mA SHDN 20k, 100nF 3473f 7
U U W U APPLICATIO S I FOR ATIO Operation
causes the FB voltage to decrease, VC increases causing A1 to enable the power section circuitry. The chip starts switch- The LT3473 combines a current mode, fixed frequency ing. If the load is light, the output voltage (and FB voltage) PWM architecture with Burst Mode micropower operation will increase until A1 turns off the power section. The output to maintain high efficiency at light loads. Operation can voltage starts to fall again. This cycle repeats and gener- best be understood by referring to the Block Diagram. ates low frequency ripple at the output. This Burst Mode The reference of the part is determined by the lower of the operation keeps the output regulated and reduces average internal 1.25V bandgap reference and the voltage at the current into the IC, resulting in high efficiency at light load. CTRL pin. The error amplifier compares voltage at the FB If the output load increases sufficiently, A1’s output remains pin with the reference and generates an error signal VC. high, resulting in continuous operation. When VC is below the Burst Mode threshold voltage, BTH, At the start of each oscillator cycle, the SR latch is set, the hysteretic comparator, A1, shuts off the power section turning on the power switch Q1. A voltage proportional to leaving only the low power circuitry running. Total current the switch current is added to a stabilizing ramp and the consumption in this state is minimized. As output loading
Switching Waveforms Switching Waveforms Transient Response
VOUT IL IL 200mV/DIV 200mA/DIV 200mA/DIV IL 200mA/DIV VSW VSW 10V/DIV 10V/DIV 11mA ILOAD 1mA V V 0.5 V 500µs/DIV 3473 AI03 IN = 3.6V 0.5µs/DIV 3473 AI01 IN = 3.6V µs/DIV 3473 AI02 IN = 3.6V V V V OUT = 20V OUT = 20V OUT = 20V I I LOAD = 50mA LOAD = 8mA
Transient Response Transient Response Transient Response
V V OUT VOUT OUT 500mV/DIV 500mV/DIV 500mV/DIV I I L L IL 500mA/DIV 500mA/DIV 500mA/DIV 51mA 55mA 75mA ILOAD ILOAD I 1mA LOAD 5mA 25mA VIN = 3.6V 500µs/DIV 3473 AI04 VIN = 3.6V 500µs/DIV 3473 AI05 VIN = 3.6V 200µs/DIV 3473 AI06 VOUT = 20V VOUT = 20V VOUT = 20V
Shutdown Waveforms Start-Up Waveforms
VOUT V 10V/DIV OUT 10V/DIV CAP 0.5V/DIV IL 500mA/DIV SHDN SHDN 5V/DIV 2V/DIV VIN = 3.6V 100µs/DIV 3473 AI07 VIN = 3.6V 500µs/DIV 3473 AI08 VOUT = 20V VOUT = 20V ILOAD = 60mA ILOAD = 30mA SHDN 20k, 100nF 3473f 7