PT6930 Datasheet, PDF (5/7 Pages) Texas Instruments – 5V TO 3.3V/2.5V 25 WATT DUAL OUTPUT INTEGRATED SWITCHING REGULATOR

Application Notes
PT6920/PT6930 Series
Using the Standby Function on the PT6920 and
PT6930 Dual Output Voltage Converters
Both output voltages of the 23-pin PT6920/6930 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
voltage is applied to V_in (pins 4, 5, & 6) with respect to
GND (pins 7–11). If a low voltage ² is then applied to pin 3,
both regulator outputs will be simultaneously disabled and
the input current drawn by the ISR will typcially drop to
less than 30mA (50mA max). The standby control may also
be used to hold-off both regulator outputs during the pe-
riod that input power is applied.
The standby pin is ideally controlled using an open-collector
(or open-drain) discrete transistor (See Figure 1). It may
also be driven directly from a dedicated TTL³ compatible
gate. Table 1 provides details of the threshold requirements.
Table 1 Inhibit Control Thresholds ^2,3
Parameter
Min
Max
Enable (VIH)
1.8V
Vin
Disable (VIL)
–0.1V
0.8V
Notes:
1. The Standby/Inhibit control logic is similar for all
Power Trends’ modules, but the flexibility and
threshold tolerances will be different. For specific
information on this function for other regulator
models, consult the applicable application note.
2. The Standby control pin is ideally controlled using an
open-collector (or open-drain) discrete transistor and
requires no external pull-up resistor. To disable the
regulator output, the control pin must be pulled to
less than 0.8Vdc with a low-level 0.5mA sink to
ground.
3. The Standby input on the PT6920/6930 series may
be driven by a differential output device, making it
directly compatible with TTL logic. The control
input has an internal pull-up to the input voltage V_in.
A voltage of 1.8V or greater ensures that the
regulator is enabled. Do not use devices that can drive
the Standby control input above 5.5V or V_in.
Figure 1
V _in
COM
Inhibit
+
C₁
22
1
4,5,6
Vin
V₂(sns)
PT6921
V₁(sns)
V 2 _out
V 1 _out
18 - 21
12 - 15
STBY GND
Vo₂(adj) V0₁(adj)
3
7 - 11
23
16
+
C₂
+
C₃
V₂out
V₁out
Q1
BSS138
COM
+5V V _in
Turn-On Time: Turning Q₁ in Figure 1 off removes the low-
voltage signal at pin 3 and enables both outputs from the
PT6920/6930 regulator. Following a delay of about 10–20ms,
Vo₁ and Vo₂ rise together until the lower voltage, Vo₂,
reaches its set output. Vo₁ then continues to rise until both
outputs reach full regulation voltage. The total power-up
time is less than 25ms, and is relatively independant of load,
temperature, and output capacitance. Figure 2 shows wave-
forms of the output voltages Vo₁ and Vo₂, for a PT6931
(3.3V/2.5V). The turn-off of Q₁ corresponds to the rise in
V_stby. The waveforms were measured with a 5Vdc input
voltage, and with resistive loads of 5A and 2A at the Vo₁
and Vo₂ outputs respectively.
Figure 2
Vo1 (3.3V)
Vo2 (2.5V)
Ch1 1V/Div Ch2 1V/Div
Timebase: 5ms/Div
Ch3 5V/Div
Vstby
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