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Application Notes
PT4400 Series
Pin-Coded Output Voltage Adjustment on the
PT4400 Programmable DC/DC Converters
The PT4400 series of isloated DC/DC converters have
a programmable output voltage. In each case the desired
output voltage must be selected from one of a number of
discrete voltages using the voltage programming control
pins. Depending on each model’s resolution and adjust-
ment range, there are up to five control pins. They are
identified VID0–VID4 (pins 7–11) respectively. By
selectively strapping these control pins to (–)Remote
Sense (pin 12), the output voltage can be programmed
in incremental steps over the defined output voltage range.
The program code and output voltage range of the PT4401
is also compatible with the “Voltage ID” code defined in
the Intel VRM 8.2 specification. Refer to Figure 1 for
the connection schematic, and the product specification
sheet for each model’s applicable program code.
Notes:
1. The programming convention is as follows:-
Logic 0:
Connect to pin 12 (–Remote Sense).
Logic 1:
Open circuit/open drain (See notes 2, & 4)
2. Do not connect pull-up resistors to the voltage
programming pins.
3. To minimize output voltage error, always use pin 12
(-Remote Sense) as the logic “0” reference. While -Vout
(pins 13-16) can also be used for programming, doing so
will degrade the voltage selection accuracy and load
regulation of the product.
4. When VID0–VID4 are all open circuit (logic 1), the
output voltage is undefined. In this state the output
voltage of the converter cannot be guaranteed, and can
vary with output load and input voltage.
Figure 1
5. On all models other than the PT4401, the contol input
VID4 (pin 11) is internally disabled and not functional.
6. 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
voltage control circuit. Discrete transistors such as the
BSS138 or IRLML2402 are examples of appropriate
devices.
Active Voltage Programming:
Special precautions should be taken when making changes
to the voltage progam code while the output is active.
This activity induces a transient, which may activate
the module’s output over-voltage (OV) protection. Once
triggered the OV protection circuit latches the output
off, and requires the momentary removal of input power
to reset the module. OV protection trips can be avoided
by limiting the output voltage adjustment to no more
than a 15% change from the initial voltage. Large transi-
tions are best made with a series of incremental changes,
allowing 100s settling time between each program state.
When using active devices to program the output voltage,
their state should be asserted prior to input power being
applied. An alternative is to pull pin 1 (Remote On/Off)
to -Vin (pins 2, 3) during the application of power, assert
the required program code, and then release pin 1. The
module will than initiate a soft-start power-up to the
desired program voltage.
L
O
A
D
PT4400
+V
sns
+V
out
-V
out
-V
sns
21
17 – 20
13 – 16
12
71 1
81 0
9
VID0 - VID4
+V
in
– V
in
4, 5
2, 3
1
Remote
On/Off
PROGRAMMING PINS
+V
OUT
+V
IN
– V
IN
– REMOTE SENSE
+ REMOTE SENSE
C
o
+
Q1
BSS138
INH
– V
OUT