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PT6526R Datasheet(PDF) 4 Page - Texas Instruments |
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PT6526R Datasheet(HTML) 4 Page - Texas Instruments |
4 / 12 page For technical support and more information, see inside back cover or visit www.ti.com Application Notes Using the Standby Function of the PT6520 Series of Integrated Switching Regulators The PT6520 series of power modules are high efficiency regulators that operate off either a 3.3V or 5V input bus voltage. These regulators incorporate a Standby function, which may be used in applications that require power-up/shutdown sequencing, and wherever there is a requirement for the output status of the module to be controlled by external circuitry. The standby function is provided by the STBY* control, pin 3. If pin 3 is left open-circuit 1 the regulator operates normally, and provides a regulated output when a valid supply voltage is applied to Vin (pins 4–6) with respect to GND (pins 7–10). If a low voltage 2 is then applied to pin 3 the regulator output will be disabled and the input current drawn by the ISR will be reduced to about 15mA 3. The standby control may also be used to hold-off the regulator output during the period that input power is applied. Pin 3 is ideally controlled with an open-collector (or open- drain) discrete transistor (See Figure 1). The open-circuit voltage is typcially 12.6V. Table 1 gives the circuit pa- rameters for this control input. Table 1 Standby Control Requirements (2, 3) Parameter Min Typ Max Input Low (VIL) –0.1V +0.4V Istby (pin 3 =ground) –0.5mA Vstby (open circuit) 12.6V 15V Notes: 1 The standby control input requires no external pull-up resistor. The open-circuit voltage of the STBY* pin is typically 12.6V. 2. The standby control input is Not compatible with TTL or other devices that incorporate a totem-pole output drive. Use only a true open-collector device, preferably a discrete bipolar transistor (or MOSFET). To ensure the regulator output is disabled, the control pin must be pulled to less than 0.4Vdc with a low-level 0.5mA sink to ground. 3. When the regulator output is disabled the current drawn from the input source is typically reduced to 15mA. Figure 1 Turn-On Time: In the circuit of Figure 1, turning Q1 on applies a low voltage to the STBY control (pin 3) and disables the regulator ouput. Correspondingly, turning Q1 off removes the low-voltage signal and enables the output. Once enabled, the output will typically experience a 10–15ms delay followed by a predictable ramp-up of voltage. The regulator should provide a fully regulated output voltage within 40ms. The waveform of Figure 2 shows the output voltage and input current waveforms of a PT6521 (3.3V) following the turn-off of Q1. The turn off of Q1 corresponds to the rise in Vstby. The waveforms were measured with a 5Vdc input voltage, and 4.5A resistive load. Figure 2 C in + C out + Inhibit V in V o COM COM PT6520 11,12,13 14 7,8,9,10 4,5,6 Vin Vo GND Vo(adj) STBY 3 Vo(sense) 1 Q1 BSS138 PT6520 Series Vo (1V/Div) Iin (2A/Div) Vstby (10V/Div) HORIZ SCALE: 5ms/Div |
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