PT8100 Datasheet, PDF (10/14 Pages) Texas Instruments – 40-A 3.3/5-V Input Programmable Integrated Switching Regulator

Application Notes
PT8100 Series
Pin-Coded Output Voltage Programming of the
40-A Rated PT8100 Series Regulators
The PT8100 series of Excalibur® ISRs incorporate a
pin-coded programmable output voltage. In each case
the desired output voltage must be selected from a preset
range defined by the regulator model. Programming is
achieved by selectively connecting the control inputs,
“VID0–VID4” (“VID 25mV–VID3” for PT8104), pins 1–5,
to the “VID Common,” pin 11. ¹ The programming code
and pinout information for each model is provided in the
PT8100 specifications. Some of the program codes are
compatible with the “Voltage ID” codes defined by the
Intel® VRM specifications. Figure 1 shows the pin-strap
connections for selecting 1.5V output voltage from a
PT8101.
Notes:
1. The programming convention is as follows:-
Logic 0: Connect to pin 11 (VID Common).
Logic 1: Open circuit/open drain (See notes 2, & 4)
2. The output voltage range of the PT8101 is limited to
2.7V maximum. Above this voltage, the performance of
the module is not guaranteed. Although the module will
appear to function above this voltage, VID 4 (pin 5)
should not be used to set the output voltage higher than
2.7V.
3. Do not connect pull-up resistors to the voltage
programming pins.
4. To minimize output voltage error, use pin 11 (VID
Common) as the logic “0” reference. However if the
regulator is used to power a VRM compatible
microprocessor this may not be possible. In this case
either connect pin 11 to pins 17–22, or the ground
plane close to the regulator. This will allow the
microprocessor to use the common ground as a VID
control reference.
4. If active devices are used to ground the voltage control
pins, low-level open-drain MOSFETs 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 output is
active. It is recommended that the ISR be powered down
or placed in standby. Changes made to the program code
while V_out is active can induce 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 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 and
VID4 with the output enabled is discouraged. The tran-
sients induced may activate the module’s over-current
protection. When using active devices to program the
output voltage, their state should be asserted prior to
input power being applied. If this is not possible, pull
STBY* (pin 6) to GND during the application of power,
assert the program code, then release pin 6. The release
of pin 6 will then to allow the device to initiate a soft-
start power-up to the program voltage.
Figure 1
V_IN
1 =OFF
GND
VID0
VID1
VID2
VID3
VID4
V_O SENSE
L_in
1µH
11
VID
Common
12–16
V_IN
5 4 3 2 1 31
VID4 – VID0 Sense
PT8101
23–30
V_OUT
V_O =1.5V
+
C_IN
STBY
6
GND
17–22
+
C_OUT
L
O
Q1
A
BSS138
D
GND
10
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