PT6364 Datasheet, PDF (9/13 Pages) Texas Instruments – 11 A 12-V Input Adjustable Integrated Switching Regulator

Application Notes
PT6360 Series
Using the Inhibit Control of the PT6360 Series of
Integrated Switching Regulators
The PT6360 series of integrated switching regulators
(ISRs) provide step-down voltage conversion for output
loads of up to 11 A. For applications that require the
output voltage to be held off, these ISRs incorporate an
Inhibit* control (pin 1). The Inhibit* control input can be
used for power-up sequencing or whenever there is a
requirement for the output voltage from the ISR to be
turned off.
The ISR functions normally with pin 1 open circuit,
providing a regulated output whenever a valid source
voltage is applied between V_in (pins 2–3) and GND (pins
5–8). When a low-level ground signal is applied to pin 1,
the regulator output is turned off ² and the input current
is significantly reduced ⁴.
Figure 4-1 shows the typical application of the Inhibit*
function. Note the discrete transistor, Q₁. The Inhibit*
control has its own internal pull-up to V_in potential. An
open-collector or open-drain device is recommended to
control this input ¹. The voltage thresholds are given in
Table 4-1.
Turn-On Time: In the circuit of Figure 4-1, turning Q₁ ¹ on
applies a low-voltage to the Inhibit* control (pin 1) and
disables the output of the regulator ². If Q₁ is then turned
off, the ISR executes a soft-start power up ³. Power up
consists of a short delay (approx. 10 msec), followed by a
period in which the output voltage rises to the full regu-
lation voltage. The module produces a regulated output
voltage in approximately 15 msec. Figure 4-2 shows the
rise in both the output voltage and input current for a
PT6363 (2.5 V), following the turn-off of Q₁. The turn
off of Q₁ corresponds to the rise in the waveform, Q₁ V_ds.
The waveforms were measured with a 12 VDC input
voltage, and 8.3-A load.
Figure 4-2
Vo (1V/Div)
Table 4-1; Inhibit Control Requirements
Parameter
Enable (VIH)
Disable (VIL)
I IL
Min
2.0 V
–0.1 V
—
Typ
—
—
–0.5 mA
Max
Vin
+0.3 V
—
Figure 4-1
V_IN
C_IN
560 µF
Inhibit
GND
+V_SENSE
12
11
2–4 _PT6363 9–10
V_OUT
1
5–8
Q₁
BSS138
C_OUT
L
330 µF
O
A
D
GND
Iin (2A/Div)
Q1 Vds (10V/Div)
HORIZ SCALE: 5ms/Div
Notes:
1. Use an open-collector device with a breakdown voltage
of at least 20 V (preferably a discrete transistor) for the
Inhibit* input. A pull-up resistor is not necessary. To
disable the output voltage the control pin should be
pulled low to less than +0.6 VDC.
2. When a ground signal is applied to the Inhibit* control
(pin 1) the module output is effectively turned off (tri-
state). The output voltage decays to zero as the load
impedance discharges the output capacitors.
3. When a ground signal to the Inhibit* pin is removed,
the regulator output initiates a soft-start cycle by first
asserting a low impedance to ground. If an external
voltage is applied to the regulator output it will sink
current and possibly overstress the module.
4. When a ground signal is applied to the Inhibit* pin, the
module is effectively turned off and the input current is
reduced to about 0.5 mA.
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