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PT5822 Datasheet(PDF) 6 Page - Texas Instruments |
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PT5822 Datasheet(HTML) 6 Page - Texas Instruments |
6 / 10 page For technical support and more information, see inside back cover or visit www.ti.com Application Notes Using the Inhibit Control of the PT5820 Series of Step-Down Regulators For applications requiring output voltage On/Off control, the PT5820 series of ISRs incorporate an inhibit function. This function can be used wherever there is a requirement for the output voltage from the ISR to be turned off. The On/Off function is provided by the Inhibit control (pin 2). The ISR functions normally with pin 2 open-circuit, providing a regulated output whenever a valid source voltage is applied between Vin (pins 5–7) and GND (pins 11–13). When a low-level ground signal is applied to pin 2, the regulator output is turned off. Figure 2-1 shows the typical application of the Inhibit function. Note the discrete transistor (Q1). The Inhibit control has its own internal pull-up to +Vin potential. An open-collector or open-drain device is required to control this input 1. The voltage thresholds are given in Table 2-1. Table 2-1; Inhibit Control Requirements Parameter Min Typ Max Enable (VIH)Vin – 0.5V — Open Disable (VIL) –0.2V — +0.8V I IL — –0.5 mA — Notes: 1. Use an open-collector device with a breakdown voltage of at least 15V (preferably a discrete transistor) for the Inhibit input. A pull-up resistor is not necessary. To disable the output voltage the control pin should be pulled low to less than +0.8VDC. 2. When a ground signal is applied to the Inhibit control (pin 2) the module output is turned off. The output voltage decays to zero as the load impedance discharges the output capacitors. 3. During the period ‘td’ in Figure 2-2 the module will assert a low impedance to ground. This will discharge any residual voltage across the output capacitors, and will crowbar any voltage supplied from external sources. Figure 2-1 Turn-On Time: In the circuit of Figure 2-1, turning Q1 on applies a low-voltage to the Inhibit control (pin 2) and disables the output of the regulator 2. If Q1 is then turned off, the ISR executes a soft-start power up. Power up consists of a short delay period, td (approx. 10-15msec) 3, followed by a period in which the output voltage rises to its full regulation voltage. The module produces a regulated output voltage within 20msec. Figure 2-2 shows the typical rise in both the output voltage and input current for a PT5821 (3.3V), following the turn- off of Q1. The turn off of Q1 corresponds to the rise in the waveform, Q1 Vds. The waveforms were measured with a 12VDC input voltage, and 10-A load. Figure 2-2 Vo (2V/Div) Iin (2A/Div) Q1 Vds (10V/Div) HORIZ SCALE: 5ms/Div td PT5820 Series PT5820 V IN 9–13 4 118 14–17 5, 6, 7 8 2 C IN 560µF C OUT 330µF 1 =Inhibit GND GND V OUT 3 Output Sense (+) Output Sense (–) Q 1 BSS138 |
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