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LTC3822-1 データシート(PDF) 6 Page - Linear Technology |
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LTC3822-1 データシート(HTML) 6 Page - Linear Technology |
6 / 24 page LTC3822-1 6 38221f PIN FUNCTIONS PLLLPF (Pin 1/Pin 2): This pin serves as the frequency select input and PLL lowpass filter compensation point. When SYNC/MODE has a DC voltage on it, tying this pin to GND selects 300kHz operation; tying this pin to VIN selects 750kHz operation. Floating this pin selects 550kHz operation. When SYNC/MODE has a clock applied to it, connect an R-C network from this pin to ground. SYNC/MODE (Pin 2/Pin 3): This pin performs two func- tions: 1) external clock synchronization input for phase- locked loop and 2) Burst Mode, pulse skipping or forced continuous mode select. Applying a clock with frequency between 250kHz and 750kHz causes the internal oscilla- tor to phase-lock to the external clock and disables Burst Mode operation, but allows pulse skipping at low load currents. To select Burst Mode operation at light loads, tie this pin to VIN. Grounding this pin selects forced continuous operation, which allows the inductor current to reverse. Tying this pin to a voltage greater than 0.4V and less than 1.2V selects pulse skipping mode. In these cases, the frequency of the internal oscillator is set by the voltage on the PLLLPF pin. TRACK/SS (Pin 3/Pin 5): Tracking Input for the Control- ler or Optional External Soft-Start Input. This pin allows the start-up of VOUT to “track” the external voltage at this pin using an external resistor divider. The LTC3822-1 regulates the VFB voltage to the smaller of 0.6V or the voltage on the TRACK/SS pin. An internal 1µA pull-up current source is connected to this pin. Tying this pin to VIN allows VOUT start-up with the internal 1ms soft-start clamp. An external soft-start can be programmed by con- necting a capacitor between this pin and ground. Do not leave this pin floating. VFB (Pin 4/Pin 6): Feedback Pin. This pin receives the remotely sensed feedback voltage for the controller from an external resistor divider across the output. ITH (Pin 5/Pin 7): Current Threshold and Error Amplifier Compensation Point. Nominal operating range on this pin is from 0.7V to 2V. The voltage on this pin determines the threshold of the main current comparator. RUN (Pin 6/Pin 8): Run Control Input. Forcing this pin below 1.1V shuts down the chip. Driving this pin to VIN or releasing this pin enables the chip to start-up. IPRG (Pin 7/Pin 10): Three-State Pin to Select the Maxi- mum Peak Sense Voltage Threshold. This pin selects the maximum allowed voltage drop between the VIN and SW pins (i.e., the maximum allowed drop across the external topside MOSFET). Tie to VIN, GND or float to select 200mV, 82mV or 125mV respectively. (DD/GN) TYPICAL PERFORMANCE CHARACTERISTICS T A = 25°C unless otherwise noted. Pulse Skip Mode Operation Burst Mode Operation VOUT 20mV/DIV AC COUPLED IL 2A/DIV VSW 2V/DIV FIGURE 10 CIRCUIT VIN = 3.3V VOUT = 1.8V, 100mA 2 µs/DIV 38221 G18 VOUT 20mV/DIV AC COUPLED IL 2A/DIV VSW 2V/DIV FIGURE 10 CIRCUIT VIN = 3.3V VOUT = 1.8V, 100mA 10 µs/DIV 38221 G19 |
同様の部品番号 - LTC3822-1 |
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同様の説明 - LTC3822-1 |
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