Datasheet LTC3901 (Analog Devices) - 6
| Hersteller | Analog Devices |
| Beschreibung | Secondary Side Synchronous Driver for Push-Pull and Full-Bridge Converters |
| Seiten / Seite | 16 / 6 — BLOCK DIAGRA. APPLICATIO S I FOR ATIO. Overview. Figure 2. Push-Pull … |
| Dateiformat / Größe | PDF / 239 Kb |
| Dokumentensprache | Englisch |
BLOCK DIAGRA. APPLICATIO S I FOR ATIO. Overview. Figure 2. Push-Pull Converter Switching Waveforms
Modelllinie für dieses Datenblatt
Textversion des Dokuments
LTC3901
W BLOCK DIAGRA
SYNC 9 SYNC+ S+ 16 VCC +1.4V 1 PVCC –1.4V SYNC– S– SYNC 3 ME AND CSE+ 6 ISE DRIVER 4 PGND 10.5mV LOGIC CSE– 5 – + DISABLE ZCSE DRIVER 11V 14 TIMER MF CSF+ 11 RESET 13 PGND 10.5mV UVLO ISF CSF– 12 – + ZCSF 11V TMR TIMER 7 R1 180k R2 ZTMR 45k 0.5 • VCC MTMR 8 10 3901 BD GND GND
U U W U APPLICATIO S I FOR ATIO Overview
the secondary side synchronous switches driven by the LTC3901’s ME and MF output. Inductor L1 and capacitor Push-pull and full bridge converters use power transform- C ers to provide input-to-output isolation and voltage step- OUT form the output filter, providing DC output voltage to the load. The feedback path from V up/down. Diodes are used as a simple solution for second- OUT through the opto- coupler driver and optocoupler back to the primary side ary side rectification. Unfortunately, as output currents controller is also shown in Figure 1. increase, the loss associated with diode forward voltage drop results in low overall efficiency. The LTC3901 over- Each full cycle of the push-pull converter consists of four comes this problem by providing control and drive for two distinct periods. Figure 2 shows the push-pull converter external N-channel synchronous MOSFETs. Synchroniza- waveforms. tion to the primary side controller is maintained through a DRVA small signal transformer. DRVB Figure 1 shows a simplified push-pull converter applica- tion. T1 is the power transformer; MA and MB are the SDRA primary side power transistors driven by the LTC3723 controller’s DRVA and DRVB outputs. The gate drive SDRB transformer T2 is driven by the LTC3723’s SDRA and SDRB outputs and provides the synchronization signal to SYNC 0V the LTC3901 on the secondary side. When both SDRA and SDRB are high, there is no voltage across the transformer’s ME primary and the LTC3901 SYNC input is approximately 0V. According to the polarity of the transformer: if SDRA goes MF 3901 F02 low while SDRB is high, SYNC is positive; if SDRB goes low while SDRA is high, SYNC is negative. ME and MF are
Figure 2. Push-Pull Converter Switching Waveforms
3901f 6
W BLOCK DIAGRA
SYNC 9 SYNC+ S+ 16 VCC +1.4V 1 PVCC –1.4V SYNC– S– SYNC 3 ME AND CSE+ 6 ISE DRIVER 4 PGND 10.5mV LOGIC CSE– 5 – + DISABLE ZCSE DRIVER 11V 14 TIMER MF CSF+ 11 RESET 13 PGND 10.5mV UVLO ISF CSF– 12 – + ZCSF 11V TMR TIMER 7 R1 180k R2 ZTMR 45k 0.5 • VCC MTMR 8 10 3901 BD GND GND
U U W U APPLICATIO S I FOR ATIO Overview
the secondary side synchronous switches driven by the LTC3901’s ME and MF output. Inductor L1 and capacitor Push-pull and full bridge converters use power transform- C ers to provide input-to-output isolation and voltage step- OUT form the output filter, providing DC output voltage to the load. The feedback path from V up/down. Diodes are used as a simple solution for second- OUT through the opto- coupler driver and optocoupler back to the primary side ary side rectification. Unfortunately, as output currents controller is also shown in Figure 1. increase, the loss associated with diode forward voltage drop results in low overall efficiency. The LTC3901 over- Each full cycle of the push-pull converter consists of four comes this problem by providing control and drive for two distinct periods. Figure 2 shows the push-pull converter external N-channel synchronous MOSFETs. Synchroniza- waveforms. tion to the primary side controller is maintained through a DRVA small signal transformer. DRVB Figure 1 shows a simplified push-pull converter applica- tion. T1 is the power transformer; MA and MB are the SDRA primary side power transistors driven by the LTC3723 controller’s DRVA and DRVB outputs. The gate drive SDRB transformer T2 is driven by the LTC3723’s SDRA and SDRB outputs and provides the synchronization signal to SYNC 0V the LTC3901 on the secondary side. When both SDRA and SDRB are high, there is no voltage across the transformer’s ME primary and the LTC3901 SYNC input is approximately 0V. According to the polarity of the transformer: if SDRA goes MF 3901 F02 low while SDRB is high, SYNC is positive; if SDRB goes low while SDRA is high, SYNC is negative. ME and MF are
Figure 2. Push-Pull Converter Switching Waveforms
3901f 6