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PT8105C Datasheet(PDF) 11 Page - Texas Instruments |
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PT8105C Datasheet(HTML) 11 Page - Texas Instruments |
11 / 14 page For technical support and more information, see inside back cover or visit www.ti.com Application Notes 11 Using the On/Off Standby Function of the PT8100 Series of Programmable ISRs The PT8100 series of programmable ISRs incorporates an On/Off Standby function. This feature may be used to turn the regulated output of the module off while input voltage is applied. This places the module in “standby” mode. The standby control may be used for power-up sequencing, or wherever there is a requirement to control the module’s output status from another circuit. The Standby function is provided by the STBY* control, pin 6. If pin 6 is left open-circuit the regulator operates normally, providing a regulated output when a valid sup- ply voltage is applied to Vin (pins 10-16) with respect to GND (pins 17-22). Connecting pin 6 to ground 1 places the regulator in standby mode 2, and reduces the input current to typically 20mA. Applying a ground signal to pin 6 prior to power-up, will inhibit the output during the period that input power is applied. When the ground signal to pin 6 is removed, the regulator initiates a soft- start to re-establish the set output voltage. 3 To ensure that the regulator output is properly enabled, the STBY* control pin must be open circuit. Table 1 Standby Control Requirements 2 Parameter Min Typ Max VIH — Open Cct. 1 VIL –0.2V — 0.8V ISTBY –0.5mA Notes: 1. The standby on a PT8100 series regulators must be controlled with an open-collector (or open-drain) transistor (See fig. 1). Do Not use a pull-up resistor. Table 1 gives the STBY* pin parameters. The control pin has an open-circuit voltage equal to Vin. To shut the regulator output off, the control pin must be “pulled” to less than 0.8Vdc with a low-impedance sink to ground. Figure 1 Figure 2 PT8100 Series 2. In the standby mode the output of the regulator is tri- state, and the output voltage falls at the rate that the load circuit discharges the output filter capacitors. 3. When the ground signal to the Standby pin is removed, the regulator output initiates a soft-start cycle by first asserting a low impedance to ground. If an external voltage is applied to the output bus, it will sink current and possibly over-stress the part. Turn-On Time Turning Q1 in Figure 1 off, removes the low-voltage signal at pin 6. After approximately 4ms the regulator output rises and reaches full regulation within 10ms. Fig. 2 shows the typical waveforms of a PT8101 following the prompt turn-off of Q1. The turn-off of Q1 corresponds to the rise in Vstby. The output voltage was set to 1.8V, and the waveforms were measured with a 5V input source, and 9.25A resistive load. L O A D C OUT + C IN + V IN V O =1.8V GND V O SENSE 1 =Off L in 1µH GND PT8101 4321 31 23–30 617–22 12–16 5 11 VID4 – VID0 Sense V IN V OUT STBY GND VID Common Q1 BSS138 Vo (1V/Div) Iin (2A/Div) Vstby (5V/Div) HORIZ SCALE: 1ms/Div |
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