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Using the Remote On/Off Function on the PTQB425080 Series of DC/DC Converters
Negative Output Enable (N Option)
Positive Output Enable (P Option)
www.ti.com........................................................................................................................................ SLTS269B – DECEMBER 2006 – REVISED NOVEMBER 2007
For applications requiring output voltage On/Off control, the PTQB425080 series of DC/DC converters
incorporate a Remote On/Off control (pin 2). This feature can be used to switch the module off without removing
the applied input source voltage. When placed in the Off state, the standby current drawn from the input source
is typically reduced to 3 mA.
Models using the negative enable option, the Remote On/Off (pin 2) control must be driven to a logic low voltage
for the converter to produce an output. This is accomplished by either permanently connecting pin 2 to –VI (pin
3), or driving it low with an external control signal.
Table 1 shows the input requirements of pin 2 for those
modules with the NEN option.
Table 1. On/Off Control Requirements
for Negative Enable
PARAMETER
MIN
TYP
MAX
VIH
Disable
2.4 V
20 V
VIL
Enable
–0.2 V
0.8 V
Vo/c
Open-Circuit
9 V
15 V
II
Pin 2 at –VI
–0.75 mA
For those models with the positive enable option, leaving pin 2 open circuit, (or driving it to an equivalent logic
high voltage), enables the converter output. This allows the module to produce an output voltage whenever a
valid input source voltage is applied to +VI with respect to –VI. If a logic-low signal is then applied to pin 2 the
converter output is disabled.
Table 2 gives the input requirements of pin 2 for modules with the PEN option.
Table 2. On/Off Control Requirements
for Positive Enable
PARAMETER
MIN
TYP
MAX
VIH
Enable
4.5 V
20 V
VIL
Disable
–0.2 V
0.8 V
Vo/c
Open-Circuit
5 V
7 V
II
Pin 2 at –VI
–0.5 mA
Notes:
1. The Remote On/Off control uses –VI (pin 3) as its ground reference. All voltages are with respect to –VI.
2. An open-collector device (preferably a discrete transistor) is recommended. A pull-up resistor is not required.
If one is added the pull-up voltage should not exceed 20 V.
Caution: Do not use a pull-resistor to +VI (pin 1). The remote On/Off control has a maximum input voltage of
20 V. Exceeding this voltage can overstress, and possibly damage, the converter.
3. The Remote On/Off pin may be controlled with devices that have a totem-pole output. This is provided the
output high level voltage (VOH) meets the module's minimum VIH specified in Table 1. If a TTL gate is used, a pull-up resistor may be required to the logic supply voltage.
4. The converter incorporates an undervoltage lockout (UVLO). The UVLO keeps the converter off until the
input voltage is close to the minimum specified operating voltage. This is regardless of the state of the
Remote On/Off control. Consult the product specification for the UVLO input voltage thresholds.
Copyright 2006–2007, Texas Instruments Incorporated
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