PT6620_14 Datasheet, PDF (5/19 Pages) Texas Instruments – Single Device: 6-A Output

Application Notes
PT6620 Series
Using the Standby Function on the PT6620 Series
of 12-V Bus Converters
For applications requiring output voltage On/Off control,
the 14-pin PT6620 ISR series incorporates a standby
function. This feature may be used for power-up/shut-
down sequencing, and wherever there is a requirement
for the output status of the module to be controlled by
external circuitry.
The standby function is provided by the STBY* control,
pin 3. If pin 3 is left open-circuit the regulator operates
normally, providing a regulated output whenever a valid
supply voltage is applied to V_in (pins 4, 5, & 6) with respect
to GND (pins 7-10). Connecting pin 3 to ground ¹ will
disable the regulator output and reduce the input current
to less than 30 mA ³. Grounding the standby control will
also hold-off the regulator output during the period that
input power is applied.
The standby input is ideally controlled with an open-
collector (or open-drain) discrete transistor (See Figure 1).
It can also be driven directly from a dedicated TTL ²
compatible gate. Table 1 provides details of the threshold
requirements.
Table 1 Inhibit Control Thresholds ^(1,2)
Parameter
Min
Max
Enable (VIH)
1V
5V
Disable (VIL)
–0.1V
0.3V
Notes:
1. The Standby input on the PT6620 regulator series may be
controlled using either an open-collector (or open-drain)
discrete transistor, or a device with a totem-pole output. A
pull-up resistor is not necessary. The control input has an
open-circuit voltage of about 1.5 Vdc. To disable the
regulator output, the control pin must be “pulled” to less
than 0.3 Vdc with a low-level 0.25 mA max. sink to ground.
2. The Standby input on the PT6620 series is also compatible
with TTL logic. A standard TTL logic gate will meet the
0.3 V V_IL(max) requirement (Table 1 ) at 0.25 mA sink
current. Do not drive the Standby control input above 5 Vdc.
3. When the regulator output is disabled the current drawn
from the input source is reduced to approximately 15 mA
(30 mA maximum).
4. The turn-off time of Q₁, or rise time of the standby input
is not critical on the PT6620 series. Turning Q₁ off slowly,
over periods up to 100 ms, will not damage the regulator.
However, a slow turn-off time will increase both the initial
delay and rate-of-rise of the output voltage.
Figure 1
V
in
COM
Inhibit
1
Vsense
4,5,6
Vin
PT6620
11,12,13
Vo
V
o
+
C _in
STBY
3
GND
Vo(adj)
7,8,9,10
14
+
C _out
Q1
BSS138
COM
+5V V_in
Turn-On Time: Turning Q₁ in Figure 1 off, removes the
low-voltage signal at pin 3 and enables the output. The
PT6620 series of regulators will provide a fully regulated
output voltage within 20ms. The actual turn-on time may
vary with load and the total amount of output capacitance.
Figure 2 shows the typical output voltage waveform of a
PT6625 (5 V) following the prompt turn off of Q₁ at time
t =0 secs. The waveform was measured with a 12-V input
voltage, and 5-A resistive load.
Figure 2
Vo (2V/Div)
0
2
4
6
8
10
12
14
16
18
t (milli - secs)
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