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PT3328 Datasheet(PDF) 7 Page - Texas Instruments |
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PT3328 Datasheet(HTML) 7 Page - Texas Instruments |
7 / 9 page For technical support and more information, see inside back cover or visit www.ti.com Application Notes Using Remote On/Off on Power Trends’ 30W Isolated DC-DC Converter Series Power Trends’ 30W isolated series of DC/DC converters incorporate a Remote On/Off function. This function may be used in applications for battery conservation, power- up/shutdown sequencing, or to co-ordinate the power-up of the regulator for active in-rush current control. (See TI application reports, SLTA021, and SLUA250). The Remote On/Off function is provided by pin 2. If pin 2 is left open-circuit, the converter provides a regu- lated output whenever a valid source voltage 1 is applied between +Vin (pins 7-9), and –Vin (pins 4-6). Applying a low voltage 2, with respect to –Vin (pin 2), disables the regulator output 3. Table 1 details the control requirements for this input. Figure 1 shows how a discrete MOSFET (Q1) may be referenced to the negative input voltage rail to control the Remote On/Off pin. Table 1 Remote On/Off Control Requirements 2 Parameter min max Enable (VIH) 2.5V 5 15V (or open circuit) 4 Disable (VIL) –0.3V 0.8V Notes: 1. These converters incorporate an “Under Voltage Lockout” (UVLO) function. This function automatically holds the converter output in the “Off” state until there is sufficient input voltage for the converter to produce a regulated output. Table 2 gives the applicable UVLO thresholds. Table 2 UVLO Thresholds Series UVLO Threshold Vin Range PT3320/4560 34 ± 2.0V 36 – 75V PT3340/4580 16.5 ± 1.5V 18 – 60V 2. The Remote On/Off control pin uses –Vin (pins 4-6) as its ground reference. All voltages specified are with respect to –Vin. 3. When the converter output is disabled the current drawn from the input supply is typically reduced to 8mA (16mA maximum). 4. The internal circuitry comprises of a high impedance (3µA -10µA) current source. The open-circuit voltage is less than 10V. 5. The Remote On/Off pin is ideally controlled using devices with an open-collector (or open-drain) output. A small low-leakage MOSFET (<100nA) is recommended. A pull-up resistor is not required, but may be necessary to ensure that the Remote On/Off pin exceeds VIH(min) (see Table 1). Do not use a pull-up resistor to the +Vin input, or drive the pin above VIH(max). Figure 1 Turn-On Time: When the Remote On/Off input is left open-circuit, the output of the converter is automatically enabled when a valid input voltage 1 is applied to the input power pins. The converter typically rises to full regulation within 30ms of the application of power (or after the release of the Remote On/Off pin with input power applied). The actual turn-on time will vary with the input voltage, output load, and the total amount of capacitance connected to the output. Using the circuit of Figure 1, Figure 2 shows the typical output voltage and input current waveforms for a PT3322/PT4562 after Q1 is turned off. The turn off of Q1 correlates with the fall of the Q1 Vgs waveform. The waveforms were measured with a 48Vdc input voltage, and 5-A resistive load. Figure 2 PT3320/3340/4560/4580 Series 30W Isolated 18 4, 5, 6 7, 8, 9 +Vin + V o u t -Vin Vo(adj) Remote On/Off 2 Sns(+) 19 10 - 12 -Vout 14 - 17 Sns(-) 13 C out + C in + Q1 BSS138 +V o –V o +V in -V in OFF/ ON C 1 0.01µF R 1 , 10 k R1 & C1 -See Note 7 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 voltage during power-up. 7. In Figure 1, Q1 is a low-threshold MOSFET. The components R1 and C1 are added to improve noise susceptibility. Vo (2V/Div) Iin (0.5A/Div) Q1Vgs (10V/Div) HORIZ SCALE: 2ms/Div |
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