PT7716 Datasheet, PDF (7/9 Pages) Texas Instruments – 20-A Low-Voltage Programmable Integrated Switching Regulator

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.
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 V_ce(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.”
Figure 4-1
+5V
STBY
COM
1µH
(Optional)
64321
VID4 - VID0
7-11
Vin
PT7710
Synch
STBY _Out
5 27
GND
13-19
26
SNS(+)
20-25
Vo
SNS(-)
12
+
C_in
L
+
C_out
O
A
D
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