PT6510_08 Datasheet, PDF (8/11 Pages) Texas Instruments – 8-A Rated Output Current

Application Notes
PT6510 Series
Using the Standby Function of the PT6510
Series of Integrated Switching Regulators
The PT6510 series of power modules incorporate a
Standby function. This may be used in applications that
require power-up/shutdown sequencing, and wherever
there is a requirement for the output status of the mod-
ule 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 whenever a
valid supply voltage is present at applied to V_in (pins 4-6)
with respect to GND (pins 7–10). Applying a ground
signal to pin 3 disables the regulator’s output and reduces
the input current to about 1 mA ⁴. 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-drain discrete
transistor ¹ (See Figure 3-1). It may also be driven directly
from a dedicated TTL ³ compatible gate. Table 3-1 gives
the circuit parameters for the control of this input.
Table 3-1 Standby Control Requirements ⁽²⁾
Parameter
Min
Typ
Max
Input Low (V_IL)
Input High (V_IH)
Input Low Current (I_IL)
–0.1 V
2V
–0.4 mA
0.4 V
V_in
Notes:
1 The standby control input is ideally controlled using an
open-drain discrete transistor. An external pull-up resistor
is not necessary. The open-circuit voltage of the STBY*
pin is the input voltage, V_in.
2. To ensure the regulator output is disabled, the control pin
must be pulled to less than 0.4 Vdc with a low-level
0.5-mA sink to ground.
3. The STBY* input is also compatible with a differential
output from standard TTL logic, providing the IC
shares the same supply voltage as the module.
4. When the regulator output is disabled the current drawn
from the input source is typically reduced to about 1 mA.
Figure 3-1
V _in
C_IN
COM
4,5,6
Vin
1
Vo (Sns)
PT6511
11–13
Vo
STBY
3
GND Vo Adj
7–10 14
C_OUT
V_o
COM
Inhibit
Q1
BSS138
V _in
Turn-On Time: In the circuit of Figure 3-1, 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 10–15 ms delay followed by a predictable ramp-up of
voltage. The regulator should provide a fully regulated
output voltage within 40 ms. The waveform of Figure 3-2
shows the output voltage and input current waveforms of
a PT6511 (3.3 V) following the turn-off of Q₁. The turn
off of Q₁ corresponds to the rise in Vstby. The waveforms
were measured with a 5 Vdc input voltage, and 4.5 A
resistive load.
Figure 3-2
Vstby (2 V/Div)
Vo (1 V/Div)
HORIZ SCALE: 2 ms/Div
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