PT6715_14 Datasheet, PDF (4/9 Pages) Texas Instruments – 13-A Output Current

Application Notes
PT6705 & PT6715 Series
Using the On/Off Standby Function on the
PT6705/6715 Excalibur™ Series of ISRs
The PT6705 and PT6715 regulator series are non-
programmable (preset voltage) versions of the PT6701,
PT6702, and PT6703 products.
The PT6705/6715 series of products incorporate an on/
off ‘standby’ function, which may be used 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 pin 2 is
connected to ground, the regulator output is disabled
and the input current drawn by the ISR typically drops
to its idle value 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 1-1 ²). The
open-circuit voltage will be approximately 12.0V. Table 1-1
gives the circuit parameters for this control input.
Table 1-1 Standby Control Requirements ^{(3, 4)}
Parameter
Min
Typ
Max
Enable (V_IH)
Disable (VIL)
Istby (pin 2 =ground)
Vstby (open circuit)
—
–0.2V
–0.5mA
12.0V
Open Circuit
0.4V
15.0V
Notes:
1. When the regulator output is disabled the current drawn
from the +V_in input source is typically reduced to 25mA
for the PT671x series, and to less than 100µA for the
PT670x series.
2. Figure 1-1 is an application schematic for the PT670x
models. This shows the requirement for an external +12V
bias supply. The +12V bias is not required for the PT671x
models. For more details, consult the applicable product
data sheet.
3. The standby control input requires no external pull-up
resistor. The open-circuit voltage of the STBY* pin is
approximately 12.0V.
4. 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.
5 After Q₁ in Figure 1-1 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 1-1
(PT6705 Series Only)
+12V
+ V _in
+
C _IN
STBY
GND
2
Stby*
4,5,6 _{V IN}
3
V _Bias
17
Sns(+)
PT6705
V_OUT ^13–16
GND Vo(adj)
8–12 1
Q1
BSS138
Sns(-)
7
+
C _OUT
V _out
GND
Turn-On Time: In the circuit of Figure 1-1, turning Q₁ on
applies a low voltage to pin 2 and disables the regulator
output. Correspondingly, turning Q₁ off removes the low-
voltage signal and enables the output ⁵. Once enabled, the
output will typically experience a 10–15ms delay followed
by a predictable ramp-up of voltage. The regulator pro-
vides a fully regulated output within 40ms. The waveforms
of Figure 1-2 show the rise of both the output voltage
and input current for a PT6706 (2.5V). The turn off of
Q₁ corresponds to the rise of V_stby. The waveform was
measured with a 5-Vdc input voltage and an 8-ADC load.
Figure 1-2
Vo (1V / DIV)
Iin (2A / DIV)
Vstby (10V / DIV)
/DIV
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