PT6880_09 Datasheet, PDF (5/10 Pages) Texas Instruments – 5A Non-Isolated Output

Application Notes
PT6880 Series
Using the On/Off Standby Function on the
PT6880 Excalibur™ Series of ISRs
The PT6880 series of integrated switching regulators
(ISRs) incorporate an on/off standby function, which
may be used to disable the regulator output. This func-
tion is provided by the STBY* control (pin 4). If pin 4 is left
open-circuit the regulator operates normally, providing a
regulated output whenever a valid supply voltage is applied
to V_in (pins 8–10) with respect to GND (pins 6, 7, & 11–
14). If the STBY* control is driven low to ground ¹, the
regulator output is disabled and the input current drawn
by the ISR drops to its idle value ².
The STBY* pin must be controlled with a low-leakage
open-collector (or open-drain) discrete transistor ^3. See
Figure 2-1 for the application schematic, and Table 2-1
for the input parameters.
Table 2-1 Standby Control Requirements
Parameter
Min
Typ
Enable (VIH)
Disable (V_IL)
Istby (pin 4 =ground)
Vstby (open circuit)
—
–0.2V
–50µA
1.4V
Max
Open Circuit
0.3V
2V
Turn-On Time: In the circuit of Figure 2-1, turning Q₁ on
applies a low voltage to pin 4 and disables the regulator
output. Correspondingly, turning Q₁ off removes the
low-voltage signal and enables the output. Once enabled
the output will typically experience a 5–10ms delay fol-
lowed by a quick ramp-up of voltage. The regulator should
provide a fully regulated output within 20ms. The wave-
forms of Figure 1-2 show the rise of both the output
voltage and input current for a PT6883 (5V). The turn
off of Q₁ corresponds to the drop of Q₁Vgs. The wave-
form was measured with a 24Vdc input voltage and 4-ADC
load.
Figure 2-2
Vo (2V/Div)
Figure 2-1
REMOTE SENSE
18
Rem Sense
V_IN
PT6880 ^{8, 9,10 V}IN
15,16,17
V_O
V_OUT
STBY*
GND
4
6, 7,
11–14
C_IN
C_OUT
L
Q₁
BSS138
O
A
D
1 =Inhibit
COM
COM
Iin (1A/Div)
Q1Vgs (10V/Div)
HORIZ SCALE: 5ms/Div
Notes:
1. To ensure that the regulator output is disabled, the
control pin must be pulled to less than 0.3Vdc with a
low-level 0.1mA sink to ground.
2. When the regulator output is disabled the current drawn
from the V_in input source is typically reduced to less than
20mA.
3. The standby control input is NOT compatible with TTL
devices that incorporate a totem-pole output drive. Use
only a true open-collector device, preferably a low-leakage
discrete bipolar transistor (or MOSFET). Do Not use a
pull-up resistor, or drive the STBY* pin with an external
voltage.
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