PT7716 Datasheet, PDF (6/9 Pages) Texas Instruments – 20-A Low-Voltage Programmable Integrated Switching Regulator

Application Notes
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 V_in (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
Disable
Istby (low)
Vstby (o/c)
2V
–0.2V
Open Cct. 1
0.8V
0.5mA
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 V_in. 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
5V
Inhibit
COM
64321
VID4 - VID0
26
Rem Sns (+)
7-11
Vin
PT7711
20-25
Vo
Synch
STBY Out
5
27
GND
13-19
Rem Sns (–)
12
+
C _in
Q1
BSS138
+
C _out
V_o =3.3V
L
O
A
D
COM
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
Vo (2V / Div)
Iin 10A / Div)
0
5
10
15
20
25
30
t (milli - secs)
* _{Consult the data sheet for details on other VID codes.}
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