PT652X Datasheet, PDF (4/8 Pages) Texas Instruments – 8-A 5-V/3.3-V Input Adjustable ISR with Short-Circuit protection

Application Notes
PT6520 Series
Using the Standby Function of the PT6520
Series of Integrated Switching Regulators
The PT6520 series of power modules are high efficiency
regulators that operate off either a 3.3V or 5V input
bus voltage. These regulators incorporate a Standby
function, which may be used in applications that require
power-up/shutdown 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 ¹ 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 7–10). If a low voltage ² is then applied
to pin 3 the regulator output will be disabled and the
input current drawn by the ISR will be reduced to about
15mA ³. The standby control may also be used to hold-off
the regulator output during the period that input power is
applied.
Pin 3 is ideally controlled with an open-collector (or open-
drain) discrete transistor (See Figure 1). The open-circuit
voltage is typcially 12.6V. Table 1 gives the circuit pa-
rameters for this control input.
Table 1 Standby Control Requirements ^{(2, 3)}
Parameter
Min
Typ
Input Low (VIL)
I_stby (pin 3 =ground)
Vstby (open circuit)
–0.1V
–0.5mA
12.6V
Max
+0.4V
15V
Notes:
1 The standby control input requires no external pull-up
resistor. The open-circuit voltage of the STBY* pin is
typically 12.6V.
2. The standby control input is Not compatible with TTL or
other 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.
3. When the regulator output is disabled the current drawn
from the input source is typically reduced to 15mA.
Figure 1
V _in
COM
Inhibit
1
Vo(sense)
4,5,6
Vin
PT6520
11,12,13
Vo
V_o
+
C _in
STBY
3
GND
Vo(adj)
7,8,9,10
14
+
C_out
Q1
BSS138
COM
Turn-On Time: In the circuit of Figure 1, turning Q₁ on applies
a low voltage to the STBY control (pin 3) 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 40ms. The waveform of
Figure 2 shows the output voltage and input current waveforms
of a PT6521 (3.3V) following the turn-off of Q₁. The turn off
of Q₁ corresponds to the rise in Vstby. The waveforms were
measured with a 5Vdc input voltage, and 4.5A resistive load.
Figure 2
Vo (1V/Div)
Iin (2A/Div)
HORIZ SCALE: 5ms/Div
Vstby (10V/Div)
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