SLTS034A Datasheet, PDF (7/10 Pages) Texas Instruments – 8A Single Device Power, Up to 90% efficiency (PT6501), Small SIP Footprint

Application Notes
PT6500 Series
Using the Standby Function on the
PT6500 5V/3.3V Bus Converters
For applications requiring output voltage On/Off control,
the 14-pin PT6500 ISR series incorporates a standby
function. This function 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 the regulator operates
normally, and provides a regulated output when a valid
supply voltage is applied to V_in (pins 4, 5, & 6) with re-
spect to GND (pins 7-10). If a low voltage² is then
applied to pin-3 the regulator output will be disabled and
the input current drawn by the ISR will drop to less than
50mA⁴. The standby control may also be used to hold-off
the regulator output during the period that input power is
applied.
The standby control 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)
Disable (VIL)
1V
–0.1V
5V
0.35V
Figure 1
V _in
COM
Inhibit
1
Vo(sense)
4,5,6
Vin
PT6500
11,12,13
Vo
V_o
+
C_in
STBY
3
GND
Vo(adj)
7,8,9,10 14
+
C_out
Q1
BSS138
COM
+5V V _in
Turn-On Time: In the circuit of Figure 1, turning Q₁ on applies a
low voltage to the Standby control (pin 3) and disables the
regulator ouput. Correspondingly, turning Q₁ off releases the
low-voltage signal and enables the output. The PT6500 ISR
series regulators have a fast response and will provide a fully
regulated output voltage within 250 µsec. The actual turn-on
time will vary with load and the total amount of output capaci-
tance. The waveform of Figure 2 shows the typical output
voltage response of a PT6501 (3.3V) following the turn-off of
Q₁ at time t = 0.0 secs. The waveform was measured with a
5Vdc input voltage, and 0.6Ω load.
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. The control input has
an open-circuit voltage of about 1Vdc. To disable the
regulator output, the control pin must be pulled to less
than 0.35Vdc with a low-level 0.5mA sink to ground.
3. The Standby input on the PT6500 series may be driven by
a differential output device, making it compatible with
TTL logic. A standard TTL logic gate will meet the
0.35V V_IL(max) requirement (Table 1 ) at 0.5mA I_OL.
Do not use devices that can drive the Standby control input
above 5Vdc.
4. When the regulator output is disabled the current drawn
from the input source is reduced to approximately 30–
40mA (50mA maximum).
Figure 2
-50
0
Vo (2V / Div)
50
100
150
200
250
300
350
t ( µs )
For technical support and more information, see inside back cover or visit www.ti.com/powertrends