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PT4529A Datasheet(PDF) 7 Page - Texas Instruments |
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PT4529A Datasheet(HTML) 7 Page - Texas Instruments |
7 / 10 page Application Notes For technical support and more information, see inside back cover or visit www.ti.com Using the Remote On/Off Function on the PT4500/ PT4520 Series of Isolated DC/DC Converters For applications requiring output voltage on/off control, the PT4500/4520 series of DC/DC converters incorporate a remote on/off function. This function may be used in applications that require battery conservation, power-up/ shutdown sequencing, and/or to coordinate the power-up of the regulator for active in-rush current control. (See the related application note, SLTA021). This function is provided by the Remote On/Off control, pin1. If pin 1 is left open-circuit, the converter provides a regulated output whenever a valid source voltage3 is applied between +Vin(pin 4, 5), and –Vin (pin 2, 3). Connecting pin 1 to pin 2, or applying a low-level signal to pin 1 (with respect to –Vin), 1 will disable the regulator output 5. Table 3-1 provides details of the interface requirements for the Remote On/Off pin. Figure 3-1 shows how a discrete MOSFET (Q1), may be referenced to the negative input voltage rail and used with this control input. Table 3-1 Inhibit Control Requirements 1 Parameter Min Max Enable (VIH) 2.5V (Open Circuit) 4 Disable (VIL) –0.3V 0.8V Notes: 1. The on/off control uses -Vin (pin 1), on the primary side of the converter, as its ground reference. All voltages specified are with respect to -Vin. 2. The on/off control internal circuitry is a high impedance 10µA current source. The open-circuit voltage may be as high as 8.3Vdc. 3. The PT4500/20 series incorporates an “Under-Voltage Lockout” (UVLO) function. The UVLO prevents operation of the converter when there is sufficient input voltage to support a regulated output. Below the UVLO threshold voltage, there is no output from the module and the Remote On/Off control is inoperative. 4. The Remote On/Off input of the PT4500/20 series must be controlled with a low-leakage (<100nA) open- drain MOSFET. Do not use a pull-up resistor. 5. When the converter output is disabled, the current drawn from the input supply is typically reduced to 8mA (16mA maximum). 6. Keep the on/off transition to less than 1ms. This prevents erratic operation of the ISR, whereby the output voltage may drift un-regulated between 0V and the rated output during power-up. Figure 3-1 Turn-On Time: The converter typically produces a fully regulated output voltage within 35ms after the removal of the low voltage signal from the Remote On/Off pin. Using the circuit of Figure 3-1, Figure 3-2 shows the output voltage and input current waveforms of a PT4521 after Q1 is turned off. The turn off of Q1 corresponds to the drop in Q1 Vgs voltage. The waveforms were mea- sured with a 48Vdc input voltage, and 2.75-A resistive load. Figure 3-2 +V in – V in +V o – V o Q1 BSS138 V GS Note 4 PT4500/4520 + Vout –Vout +Vin –Vin Remote On/Off V o (adj) 1 2, 3 4, 5 9,10 7, 8 6 PT4500/4520 Series Vout (2V/Div) Iin (0.2A/Div) Q1 Vgs (10V/Div) HORIZ. SCALE: 5ms/Div |
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