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PT5526N Datasheet(PDF) 6 Page - Texas Instruments |
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PT5526N Datasheet(HTML) 6 Page - Texas Instruments |
6 / 9 page Application Notes For technical support and more information, see inside back cover or visit www.ti.com PT5500/5520 Series Using the Inhibit Control on the PT5500/PT5520 Series of Excalibur Step-Down ISRs For applications requiring output voltage On/Off control, both the PT5500 and PT5520 series of power modules incorporate an inhibit function. This function can be used for power-up sequencing or wherever there is a require- ment for the module to be switched off. The On/Off function is provided by the Inhibit (pin 1) control. The ISR functions normally with Pin 1 open-circuit, providing a regulated output whenever a valid source voltage is applied to Vin, (pin 2). When a low-level2 ground signal is applied to pin 1, the regulator output will be disabled. Figure 1 shows an application schematic, which details the typical use 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 pin. The Inhibit pin control thresholds are given in Table 1. Equation 1 may be used to determine the approximate current drawn from the input source, and by Q1 when the regulator is in the inhibit state. Table 1; Inhibit Control Requirements Parameter Min Max Enable (VIH)Vin – 0.5 Open Disable (VIL) –0.2V+0.5V Equation 1 Iinh =Vin ÷ 10kΩ ± 20% Notes: 1. Use an open-collector device (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 +0.5VDC. 2. Do not control the Inhibit input with an external DC voltage. This will lead to erratic operation of the ISR and may over-stress the regulator. 5. Avoid capacitance greater than 500pF at the Inhibit control pin. Excessive capacitance at this pin will cause the ISR to produce a pulse on the output voltage bus at turn-on. 6. Keep the On/Off transition to less than 10µs. This prevents erratic operation of the ISR, which could cause a momentary high output voltage. Figure 1 Turn-On Time: In the circuit of Figure 1, turning Q1 on applies a low-voltage to the Inhibit control (pin 1) and disables the regulator output. Correspondingly, turning Q1 off allows the Inhibit control pin to be pulled high by its internal pull-up resistor. The ISR produces a fully regulated output voltage within 10-msec of the release of the Inhibit control pin. The actual turn-on time will vary with input voltage, output load, and the total amount of load capacitance. Figure 2 shows the typical rise in both output voltage and input current for a PT5502 (2.5V) following the turn-off of Q1 at time t =0. The waveform was measured with a 5Vdc input voltage, and 2.5A resistive load. Figure 2 C2 100 µF + C1, 1 µF (Optional) +V O COM +V IN COM Inhibit Q1 BSS138 PT5502 2 13 4 Vin V o GND INH -1 0 1 23 456 78 t (milli-secs) Vo (1V / Div) IIN (1A / Div) VINH (5V / Div) |
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