PT7761-5V Datasheet, PDF (7/8 Pages) Texas Instruments – 40-A Programmable Integrated Switching Regulator Module

Application Notes
PT7761
Pin-Coded Output Voltage Adjustment of
PT7761 “Excalibur™” ISRs
The PT7761 Excalibur power module incorporates a
pin-coded output voltage control. These regulators in-
clude five control pins, identified VID0–VID4 (pins 1–5)
respectively. By selectively grounding VID0-VID4, the
output voltage of this regulator can be programmed in
incremental steps over the output voltage range, 1.3V to
3.5V. The program code and voltage range is designed to
be compatible with the “Voltage ID” specification defined
for popular microprocessors. Refer to Figure 1 for the
connection schematic, and the applicable data sheet for
the program code.
Notes:
1. The programming convention is as follows:-
Logic 0: Connect to pin15 (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 15 (Rem Sense Gnd) as the logic “0” reference.
While the regular ground (pins 16–22) can also be used for
programming, doing so will degrade the load regulation of
the product. If the remote sense ground is not used,
pin 15 must be connected to pin 16 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
voltage control circuit. Discrete transistors such as the
BSS138, 2N7002, IRLML2402, are examples of
appropriate devices.
Active Voltage Programming:
Special precautions should be taken when making changes
to the voltage control progam code while the unit is
powered. It is highly recommended that the ISR be either
powered down or held in standby. Changes made to the
program code while V_out is enabled induces high current
transients through the device. This is the result of the
electrolytic output capacitors being either charged or dis-
charged 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 recommended. Making non-incremental
changes to VID3 and VID4 with the output enabled is
discouraged. If they are changed, the transients induced
can overstress the device. If the program code cannot be
asserted prior to power-up, pull pin 6 (STBY) to GND
during the period that the input voltage is applied. The
release of pin 6 will then to allow the device to initiate a
soft-start power-up to the program voltage.
Figure 1
+5V
1 µH
(Optional)
STBY
COM
+
C_in
54321
VID0 - VID4
31
Sns (+)
9–14
V_IN
PT7761
23–30
V_OUT
Stby Sync GND Sns (–)
67
16–22 15
L
+
C_out
O
A
D
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