PT6121 Datasheet, PDF (5/7 Pages) Texas Instruments – 1 AMP ADJUSTABLE LOW VOLTAGE INPUT INTEGRATED SWITCHING REGULATOR

Application Notes
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PT6100/6120/6210/6220/6300/6320 Series
More Application Notes
Using the Inhibit Function on Power Trends’
Wide Input Range Bus ISRs
For applications requiring output voltage On/Off control, the
12pin ISR products incorporate an inhibit function. The func-
tion has uses in areas such as battery conservation, power-up
sequencing, or any other application where the regulated output
from the module is required to be switched off. The On/Off
function is provided by the Inhibit control, pin 1.
The ISR functions normally with pin 1 open-circuit, providing a
regulated output whenever a valid source voltage is applied to
V_in, (pins 2, 3, & 4). When a low-level² ground signal is applied
to pin 1 the regulator output is disabled, and the input current to
the ISR is reduced to about 100µA ^3/.
Figure 1 shows an application schematic, which details the typi-
cal use of the inhibit function. Note the discrete transistor, Q1.
The inhibit control has its own internal pull-up with a maximum
open-circuit voltage of 8.3VDC. Only devices with a true open-
collector or open-drain output can be used to control this pin. A
discrete bipolar transistor or MOSFET is recommended.
Notes:
1. The inhibit control logic is similar for all Power Trends’
modules, but the flexibility and threshold tolerances will be
different. For specific information on the inhibit function of
other ISR models, consult the applicable application note.
2. Use only a true open-collector device (preferably a discrete
transistor) for the inhibit input. Do Not use a pull-up resis-
tor, or drive the input directly from the output of a TTL or
other logic gate. To disable the output voltage, the control
pin should be pulled low to less than +1.5VDC.
3. The following equation may be used to determine the ap-
proximate current drawn from the input supply at V_in, and
through Q1 when the inhibit is active.
I_stby = V_in ÷ 155kΩ ± 20%
4. When the inhibit control pin is active, i.e. pulled low, the
maximum input voltage is limited to +30Vdc.
5. Do not control the inhibit input with an external DC volt-
age. This will lead to erratic operation of the ISR and may
over-stress the regulator.
6. Avoid capacitance greater than 500pF at the Inhibit control
pin. Excessive capacitance at this pin will cause the ISR to
produce a pulse on the output voltage bus at turn-on.
7. Keep the On/Off transition to less than 10µs. This prevents
erratic operation of the ISR, which can cause a momentary
high output voltage.
Figure 1
V _in
C1, 1 µF
(Optional)
Inh
COM
PT6100/6210/6300
2,3,4
9,10,11
Vin
Vo
Inh
GND Vo(adj)
1
5,6,7,8 12
Q1
2N7002
C2
+
100 µF
V _out
COM
Turn-On Time: The output of the ISR is enabled automatically
when external power is applied to the input. The Inhibit control
pin is pulled high by its internal pull-up resistor. The ISR pro-
duces a fully regulated output voltage within 1-msec of either the
release of the Inhibit control pin, or the application of power.
The actual turn-on time will vary with the input voltage, output
load, and the total amount of capacitance connected to the out-
put Using the circuit of Figure 1, Figure 2 shows the typical rise
in output voltage for the PT6101 following the turn-off of Q1 at
time t =0. The waveform was measured with a 9Vdc input volt-
age, and 5-Ohm resistive load.
Figure 2
6
5
4
3
2
1
0
-0.2
0
0.2
0.4
0.6
0.8
1
t (milli-secs)
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 [phone] Fax: [phone] http://www.powertrends.com
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