SLTS102A Datasheet, PDF (5/8 Pages) Texas Instruments – 14-A 12V-Input Adjustable Integrated Switching Regulator

Application Notes
PT6725 Series
Using the Standby Function of the PT6725
Series of Integrated Switching Regulators
The PT6725 series of power modules are high efficiency
regulators that operate off a +12V input bus voltage.
These regulators incorporate an on/off ‘Standby’ func-
tion, which may be used to disable the regulator output.
The standby function is provided by the STBY* control,
pin 2. If pin 2 is left open-circuit the regulator operates
normally, and provides a regulated output when a valid
supply voltage is applied to V_in (pins 4–6) with respect to
GND (pins 8–12). If a low voltage ³ is then applied to
pin 2 the regulator output will be disabled and the input
current drawn by the ISR will be reduced to 0.5mA ¹.
The standby control may also be used to hold-off the
regulator output during the period that input power is
applied.
Pin 2 is ideally controlled with an open-collector (or
open-drain) discrete transistor (See Figure 1). The open-
circuit voltage is typcially the input voltage V_in. Table 1
gives the circuit parameters for this control input.
Table 1 Standby Control Requirements ^{(2, 3)}
Parameter
Min
Typ
Input Low (VIL)
Istby (pin 2 =ground)
Vstby (open circuit)
–0.1V
—
—
–0.5mA
Vin
Max
+0.4V
—
—
Notes:
1. When the regulator output is disabled the current drawn
from the +V_in input source is typically reduced to 0.5mA.
2 The standby control input requires no external pull-up
resistor. The open-circuit voltage of the STBY* pin is
approximately th input voltage V_in (+12V).
3. The standby control input is Not compatible with TTL
devices that incorporate a totem-pole output drive. Use
only a true open-collector device, preferably a discrete
bipolar transistor (or MOSFET). To ensure the regulator
output is disabled, the control pin must be pulled to less
than 0.4Vdc with a low-level 0.5mA sink to ground.
4. After Q₁ in Figure 1 is turned off and before the output
begins to rise, the regulator output will assert a low
impedance to ground. If an external voltage is applied to
the output it will sink current and possibly over-stress the
part.
Figure 1
+V_in
+
C_IN
STBY
GND
2
STBY*
17
Sense(+)
4–6 _VIN
PT6725 ^VOUT ^13–16
V_out
GND Vo(adj) Sense(–)
8–12 1
7
Q1
BSS138
+
C _OUT
GND
Turn-On Time: In the circuit of Figure 1, turning Q₁ on
applies a low voltage to the STBY control (pin 2) and
disables the regulator ouput. Correspondingly, turning
Q₁ off removes the low-voltage signal and enables the
output. Once enabled, the output will typically experience
a 10–15ms delay followed by a predictable ramp-up of
voltage. The regulator should provide a fully regulated
output voltage within 30ms. Figure 2 shows the output
voltage response, V_o, of a PT6726 (2.5V) following the
turn-off of Q₁. The turn-off of Q₁ corresponds to the
rise in V_stby. The waveform was measured with a 12Vdc
input voltage, and 9.3ADC resistive load.
Figure 2
Vo (1V/Div)
HORIZ SCALE: 5ms/Div
Vstby (10V/Div)
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