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TPS62623 Datasheet(PDF) 8 Page - Texas Instruments |
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TPS62623 Datasheet(HTML) 8 Page - Texas Instruments |
8 / 28 page TPS62620, TPS62621, TPS62622 TPS62623, TPS62624, TPS62625 SLVS848D – JULY 2009 – REVISED OCTOBER 2015 www.ti.com 8.3 Feature Description 8.3.1 Mode Selection The MODE pin allows to select the operating mode of the device. Connecting this pin to GND enables the automatic PWM and power-save mode operation. The converter operates in regulated frequency PWM mode at moderate to heavy loads and in the PFM mode during light loads, which maintains high efficiency over a wide load current range. Pulling the MODE pin high forces the converter to operate in the PWM mode even at light load currents. The advantage is that the converter operates with a fixed frequency that allows simple filtering of the switching frequency for noise-sensitive applications. In this mode, the efficiency is lower compared to the power-save mode during light loads. For additional flexibility, it is possible to switch from power-save mode to forced PWM mode during operation. This allows efficient power management by adjusting the operation of the converter to the specific system requirements. 8.3.2 Enable The device starts operation when EN is set high and starts up with the soft start. For proper operation, the EN pin must be terminated and must not be left floating. Pulling the EN pin low forces the device into shutdown, with a shutdown quiescent current of typically 0.1 μA. In this mode, the P- and N-channel MOSFETs are turned off, the internal resistor feedback divider is disconnected, and the entire internal-control circuitry is switched off. 8.3.3 Undervoltage Lockout The undervoltage lockout circuit prevents the device from misoperation at low input voltages. It prevents the converter from turning on the switch or rectifier MOSFET under undefined conditions. The TPS6262x devices have a UVLO threshold set to 2.05 V (typical). Fully functional operation is permitted down to 2.1 V input voltage. 8.3.4 Thermal Shutdown As soon as the junction temperature, TJ, exceeds typically 140°C, the device goes into thermal shutdown. In this mode, the P- and N-channel MOSFETs are turned off. The device continues its operation when the junction temperature again falls below typically 130°C. 8.4 Device Functional Modes 8.4.1 Soft Start The TPS6262x devices have an internal soft-start circuit that limits the inrush current during start-up. This limits input voltage drops when a battery or a high-impedance power source is connected to the input of the converter. The soft-start system progressively increases the on-time from a minimum pulse-width of 35 ns as a function of the output voltage. This mode of operation continues for ca. 100 μs after enable. Should the output voltage not have reached its target value by this time, such as in the case of heavy load, the soft-start transitions to a second mode of operation. The converter then operates in a current limit mode, specifically the P-MOS current limit is set to half the nominal limit, and the N-channel MOSFET remains on until the inductor current has reset. After a further 100 μs, the device ramps up to the full current limit operation if the output voltage has risen above 0.5 V (approximately). Therefore, the start-up time mainly depends on the output capacitor and load current. 8.4.2 Switching Frequency The magnitude of the internal ramp, which is generated from the duty cycle, reduces for duty cycles either set of 50%. Thus, there is less overdrive on the main comparator inputs which tends to slow the conversion down. The intrinsic maximum operating frequency of the converter is about 10 MHz to 12 MHz, which is controlled to circa 6 MHz by a frequency locked loop. 8 Submit Documentation Feedback Copyright © 2009–2015, Texas Instruments Incorporated |
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