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PT7745N Datasheet(PDF) 7 Page - Texas Instruments |
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PT7745N 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 PT7710 Family Pin-Coded Output Voltage Adjustment of the PT7710 Excalibur™ Series of 20-A ISRs The PT7710 Excalibur™ family of converters incorporate a pin-coded control to adjust the output voltage. This feature uses the control pins VID0–VID4 (pins 1–6). When the control pins are left open-circuit, the ISR output regulates at its default output voltage. Each control pin is internally connected to a precision resistor, which when grounded applies a weighted change to the output voltage. By selectively grounding VID0–VID4, the output voltage of these ISRs can be programmed in incremental steps over the specified output voltage range. The program codes and output voltage range offered by these ISRs are compatible with the Voltage ID specifica- tions defined by Intel Corporation for VRMs (voltage regulator modules). The codes are used by both the Pentium® and Athlon® microprocessors. Refer to Figure 4-1 for the connection schematic, and the respective device Data Sheet for the programming code information. Notes: 1. The programming convention is as follows:- Logic 0: Connect to pin 12 (Remote Sense Ground). Logic 1: Open circuit/open drain (See notes 2, & 4) 2. Do not connect pull-up resistors to the voltage programming pins. 3. Use pin 12 (Remote Sense Ground) as the logic “0” reference. While the regular ground (pins 13-19) can also be used for programming, doing so will degrade the load reglation of the product. If the remote sense ground is not used, pin 12 must be connected to pin 13 for optimum output voltage accuracy. Figure 4-1 4. If active devices are used to ground the voltage control pins, low-level open drain MOSFET devices should be used over bipolar transistors. The inherent Vce(sat) in bipolar devices introduces errors in the device’s internal divider network. Discrete transistors such as the BSS138, 2N7002, or IRLML2402 are examples of appropriate devices. Active Voltage Programming: Special precautions should be taken when making changes to the output voltage progam code while the unit is powered. This activity can induce current transients through the device as a result of the electrolytic output capacitors being either charged or discharged to the new output voltage set-point. The transient current can be minimized by making only incremental changes to the binary code, i.e. one LSB at a time. A minimum of 100µs settling time between each program state is also recom- mended. Making non-incremental changes to VID3 or VID4 is discouraged. When active devices are used to program the output voltage, their state should be asserted prior to the input power being applied. An alternative is to pull pin 5 (STBY) control to GND during the application of input voltage, then assert the required program code and release pin 5. The module will then intiate a soft-start power-up to the desired program voltage. For more information on the use of the Standby function, consult the related applica- tion note, “Using the Standby Function on the PT7710 Excalibur™ Series of 20-A ISRs.” C out + C in + 1µH (Optional) +5V COM STBY L O A D PT7710 64321 26 20-25 12 5 13-19 27 7-11 Vo Vin GND SNS(+) SNS(-) Synch Out STBY VID4 - VID0 |
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