
Application Notes
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PT7710 Family
Using the Standby Function on the PT7710
Excalibur Series of 20-A ISRs
For applications requiring On/Off control of the output
voltage, the PT7710 family of Excalibur ISRs incorpo-
rate a standby function. This feature may be used for
power-up/shutdown sequencing, or to change the output
voltage while input power is applied. See related notes:
“Pin-Coded Output Voltage Adjustment of the PT7710
Excalibur Series of 20-A ISRs.”
The standby function is provided by the STBY* control,
pin 5. If pin 5 is left open-circuit the regulator operates
normally, providing a regulated output whenever a valid
supply voltage is applied to Vin (pins 7-11) with respect to
GND (pins 13-19). Connecting pin 5 to ground 1 will set
the regulator output to zero volts 2. This places the regu-
lator in standby mode, and reduces the input current to
typcially 30mA (60mA max). If a ground signal is applied
to pin 5 prior to power-up, the regulator output will be
held at zero volts during the period that input power is
applied.
The standby input must be controlled with an open-
collector (or open-drain) discrete transistor (See Figure 1).
Table 3-1 gives the input requirements.
Table 3-1 Standby Control Input Requirements (1, 2)
Parameter
Min
Typ
Max
Enable
2V
Open Cct. 1
Disable
–0.2V
0.8V
Istby (low)
0.5mA
Vstby (o/c)
Vin
Notes:
1. The Standby input on the PT7710 regulator family must
be controlled using an open-collector (or open-drain)
discrete transistor. Do Not use a pull-up resistor. The
control input has an open-circuit voltage equal to Vin. To
set the regulator output to zero, the control pin must be
“pulled” to less than 0.8Vdc with a 0.5mA sink to ground.
2. When placed in the standby mode, the regulator output
discharges the output capacitance with a low impedance to
ground.
3. The turn-off time of Q1, or rise time of the standby input
is not critical with the PT7710 family. Turning Q1 off
slowly, over periods up to 100ms, will not affect regulator
operation. However, a slow turn-off time will increase
both the initial delay and rise-time of the output voltage.
Figure 3-1
Turn-On Time:
Turning Q1 in Figure 3-1 off, removes the
low-voltage signal at pin 5 and enables the output. After
a delay of approximately 10ms, the output voltage of a
PT771x regulator rises to full regulation within 30ms 3.
Figure 3-2 shows the typical output voltage waveform of
a PT7711 following the turn-off of Q1 at time t =0 secs.
The output voltage in Figure 3-1 is set to 3.3V by connecting
VID0 (pin 1), VID2 (pin 3), and VID3 (pin 4) to the ‘Rem
Sense Gnd’ (pin 12)*. The waveform was measured with a
+5V input source voltage, and 10-A resistive load.
Figure 3-2
C
out
+
C
in
+
5V
COM
Inhibit
L
O
A
D
PT7711
6432
1
26
20-25
12
5
13-19
27
7-11
Vo
Vin
GND
Rem Sns (+)
Synch
Out
STBY
VID4 - VID0
Rem Sns (–)
V
o
=3.3V
COM
Q1
BSS138
* Consult the data sheet for details on other VID codes.
0
5
10
15
20
25
30
t (milli - secs)
Vo (2V / Div)
Iin 10A / Div)