PT7615 Datasheet, PDF (6/7 Pages) Texas Instruments – 20-A Low-Voltage Programmable Integrated Switching Regulator

Application Notes
PT7708/09, PT7615
Pin-Coded Output Voltage Adjustment of
20-A Programmable Regulators
The 20-A family of programmable ISRs 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 module’s output voltage range. The program
codes and output voltage range offered by these ISRs are
compatible with the Voltage ID specifications defined by
Intel Corporation for VRMs (voltage regulator mod-
ules). The codes are used by both the Pentium® and
Athlon® microprocessors. Refer to Figure 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 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
discharged to the new output voltage set-point. The
transient current can be minimized by making only in-
cremental 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 or VID4 while the output
is enabled is discouraged. The transients induced can
overstress the device. If the program code cannot be
asserted priot to power-up, pull pin 5 (STBY) control to
GND during the period that the input voltage is applied
to V_in. Releasing pin 5 will then allow the device to per-
form a soft-start to the programmed voltage. For more
information on the use of the Standby function, consult
the related application note, “Using the Standby Function
on 20-A Programmable Switching Regulators”
Figure 1
+5V
STBY
COM
1µH
(Optional)
64321
VID4 - VID0
26
SNS(+)
7-11
Vin
PT770X/PT761X
20-25
Vo
Synch
STBY _Out
5 27
GND
13-19
SNS(-)
12
+
C_in
L
+
C_out
O
A
D
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