PT6980 Datasheet, PDF (11/12 Pages) Texas Instruments – 10-A 12V-Input Dual Output Integrated Switching Regulator

Application Notes
PT6980 Series
Using the Standby Function on the PT6980
Series of Dual-Output Voltage Regulators
Both output voltages of the 23-pin PT6980 dual-output
converter may be disabled using the regulator’s ‘Standby’
function. This function may be used in applications that
require power-up/shutdown sequencing, or wherever there
is a requirement to control the output voltage On/Off status
with external circuitry.
The standby function is provided by the STBY* control
(pin 3). If pin 3 is left open-circuit the regulator operates
normally, and provides a regulated output at both Vo₁ (pins
12–15) and Vo₂ (pins 18–21) whenever a valid supply volt-
age is applied to V_in (pins 4, 5, & 6) with respect to GND
(pins 7-11). If a low voltage¹ is then applied to pin-3 both
regulator outputs will be simultaneously disabled and the
input current drawn by the ISR will drop to a typical value
of 4mA. The standby control may also be used to hold-off
both regulator outputs during the period that input power is
applied.
The standby pin is ideally controlled using an open-collector
(or open-drain) discrete transistor (See Figure 1). The
open-circuit voltage is the input voltage +V_in. Table 1 gives
the circuit parameters for this control input.
Table 1 Standby Control Parameters ^{1, 2}
Parameter
Min
TYP
Enable (VIH)
Disable (VIL)
VSTBY (open circuit)
I_STBY (I_IL)
—
–0.1V
—
—
—
—
+Vin 2
—
Max
Open circuit
0.4V 1
—
–0.5mA
Figure 1
V_in
Inhibit
COM
22
1
4, 5, 6 _VIN
V₂(sns)
PT6984
V₁(sns)
Vo₂ ^18–21
Vo₁ ^12–15
STBY GND V₂(adj) V₁(adj)
+
3
7–11 23 16
C₁
Q1
BSS138
+
C₂
Vo₂
Vo₁
+
C₃
COM
Turn-On Time: Turning Q₁ in Figure 1 off removes the low-
voltage signal at pin 3 and enables the PT6980 series
regulator. Following a delay of about 25ms, Vo₁ and Vo₂
rise together until the lower voltage, Vo₂, reaches its set
output. Vo₁ continues to rise until both outputs reach full
regulation voltage. The total power-up time is less than
40ms, and is relatively independent of load, temperature,
and output capacitance. Figure 2 shows waveforms of the
output voltages, Vo₁ and Vo₂, for a PT6984 (3.3V/1.2V).
The turn-off of Q₁ corresponds to the rise in V_STBY. The
waveforms were measured with a 12V input voltage, and
with resistive loads of 5A and 1.25A at the Vo₁ and Vo₂
outputs respectively.
Figure 2
Notes:
1. 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.
2 The standby control input requires no external pull-up resistor.
The open-circuit voltage of the STBY* pin is the input
voltage +V_in.
3. When the regulator output is disabled the current drawn from
the input source is typically reduced to 4mA.
HORIZ SCALE: 5ms/Div
V1 (1V/Div)
V2 (1V/Div)
Vstby (10V/Div)
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