PT6653E Datasheet, PDF (5/16 Pages) Texas Instruments – Single Device: 5-A Output Input Voltage Range: 9 V to 28 V 12 V / 24 V Input Compatible

Application Notes
PT6650 Series
Using the Standby Function on the PT6650 Series
of 12/24-V Input Bus Converters
For applications requiring output voltage On/Off control,
the 14-pin PT6650 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-drain
discrete transistor (See Figure 2-1). It can also be driven
directly from a dedicated TTL ² compatible gate. Table 2-1
provides details of the threshold requirements.
Table 2-1 Inhibit Control Thresholds ^{(1, 2)}
Parameter
Min
Max
Enable (VIH)
Disable (VIL)
1V
–0.1 V
5V
0.3 V
Notes:
1. The Standby input on the PT6650 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 maximum sink to
ground.
2. The Standby input on the PT6650 series is also compatible
with TTL logic. A standard TTL logic gate will meet the
0.3 V V_IL(max) requirement (Table 2-1 ) 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 PT6650 series. Turning Q₁ off 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 2-1
V
in
COM
Inhibit
1
Vsense
4,5,6
Vin
PT6650
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 off in Figure 2-1, removes the
low-voltage signal at pin 3 and enables the output. The
PT6650 series of regulators will provide a fully regulated out-
put voltage within 12 ms. The actual turn-on time may
vary with load and the total amount of output capacitance.
Figure 2-2 shows the typical output voltage waveform of a
PT6653 (5 V) following the prompt turn-off of Q₁ at time
t =0 secs. The waveform was measured with a 24 V input
voltage, and 5 A resistive load.
Figure 2-2
Vo (2V/Div)
0
2
4
6
8
10
12
t (milli - secs)
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