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Application Notes
PT4400/4410 Series
Using the Remote On/Off Function on the
PT4400/PT4410 Series of DC/DC Converters
For applications requiring output voltage On/Off control,
these converters incorporate a
“Remote On/Off”
control
(pin 1). This feature can be used to switch the module
off without removing the applied input source voltage.
The converter functions normally with Pin 1 open-circuit,
providing a regulated output voltage when a valid source
voltage is applied to +V
in
(pins 4, 5), with respect to
-V
in
(pins 2, 3). When a low-level
1
ground signal is
applied to pin 1, the converter output will be turned off.
Figure 1 is an application schematic, which shows the
typical use of the
Remote On/Off
function. Note the dis-
crete transistor (Q
1
). The Remote On/Off pin has its
own internal pull-up, allowing it to be controlled with an
open-collector or open-drain device (See notes 2 & 3).
Table 1 gives the threshold requirements.
When placed in the “Off” state, the standby current drawn
from the input source is typically reduced to less than 1mA.
Table 1; Pin 1 Remote On/Off Control Requirements
1
Parameter
Min
Typ
Max
Enable (VIH)
Disable (VIL)
Vo/c [Open-Circuit]
Iin [pin 1 at –Vin]
4.5 V
—
—
—
—
0.8 V
5.0 V
—
—
–0.5 mA
Notes:
1. The
Remote On/Off
control uses –V
in
(pins 2, 3) as its
ground reference. All voltages are with respect to –V
in
.
2. Use an open-collector device (preferably a discrete
transistor) for the
Remote On/Off
input. A pull-up
resistor is not necessary. To disable the output voltage,
the control pin should be pulled low to less than +0.8 V.
3. The
Remote On/Off
pin may be controlled with devices that
have a totem-pole output. This is provided the output
high-level voltage (V
OH
) meets the module’s minimum
V
IH
specified in Table 1.
Do not
apply more than +20 V.
If a TTL gate is used, a pull-up resistor may be required to
the logic supply voltage.
4. The converter incorporates an “Under-Voltage Lockout”
(UVLO). The UVLO keeps the converter off until
the input voltage is close to the minimum specified
operating voltage. This is regardless of the state of
the
Remote On/Off
control. Table 2 gives the UVLO
input voltage thresholds.
Figure 1
Turn-On Time:
In the circuit of Figure 1, turning Q
1
on
applies a low-voltage to pin 1 and disables the converter
output. Correspondingly, turning Q
1
off allows pin 1
to
be pulled high by an internal pull-up resistor. The con-
verter produces a regulated output voltage within 50ms.
Figure 2 shows the output response of a PT4401 following
the turn-off of Q
1
. The turn off of Q
1
corresponds to the
drop in Q
1
Vgs. Although the rise-time of the output
voltage is short (<5 ms), the indicated delay time will
vary depending upon the input voltage and the module’s
internal timing. The output voltage of the PT4401 was
set to 3.3 V by connecting VID0 (pin 7), VID2 (pin 9),
and VID3 (pin 10) to the (–)Remote Sense (pin 12). The
waveforms were measured with 48 VDC input voltage,
and a 10 A resistive load.
Figure 2
L
O
A
D
PT4401
+V
s n s
+V
out
-V
out
-V
s n s
21
17
–
20
13
–
16
12
7
11
8
10
9
VID0 - VID4
+V
in
–
V
in
4, 5
2, 3
1
Remote
On/Off
PROGRAMMING PINS
+3.3V
+V
IN
–
V
IN
0V
–
REMOTE SENSE
+ REMOTE SENSE
C
o
+
R1
10k
Q1
BSS138
Vdd
1 =OFF
Note 1
U1a
Note 1
Note 1
Table 2; UVLO Thresholds
4
Series
V
in
Range
UVLO Threshold
PT4400/4410
36 – 75 V
32V ±2 V
Vo (1V/Div)
Iin (1A/Div)
Q1 Vgs (10V/Div)
HORIZ SCALE: 5ms/Div
Delay Time