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参数资料
| 型号： | PT4801A |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 电源模块 |
| 英文描述： | 3-OUTPUT 25 W DC-DC REG PWR SUPPLY MODULE |
| 封装： | SIP-15 |
| 文件页数： | 4/9页 |
| 文件大小： | 182K |
| 代理商： | PT4801A |
For technical support and more information, see inside back cover or visit www.ti.com
Using the Remote On/Off Control on the PT4801
Triple-Output Voltage DC/DC Converter
The three output voltages of the PT4801 triple-output
DC/DC converter may be simultaneously disabled using
the Remote On/Off control. This control is used in appli-
cations that require power-up/shutdown sequencing, or
wherever there is a requirement to control the on/off sta-
tus of the module with external circuitry.
On/off control of the PT4801 is provided by pin 1. If
pin 1 is left open-circuit the regulator operates normally,
and provides a regulated output at all three outputs, Vo1
(pin 10), Vo2 (pins 14, 15), and Vo3 (pin 18), whenever a
valid input voltage is applied to ±Vin. If a low voltage is
then applied to pin 1, the module’s output will be disabled
and the input current it draws will drop to a typical value
of 8mA. The Remote On/Off input may also be used to hold
the module’s output in the ‘off’ state during the period
that input power is applied. The input is ideally controlled
using an open-collector (or open-drain) discrete transistor
(See Figure 1) 3.
Table 1 Remote On/Off Control Parameters 1, 2
Parameter
Min
Typ
Max
Enable (VIH)2.5V
—
15V 3
Disable (VIL)–0.1V
—
0.8V
Notes:
1. The Remote On/Off input uses –Vin (pins 3 & 4) as a
ground reference, and cannot be directly controlled
from circuitry referenced to the isolated output ±Vo.
2. The internal circuitry comprises of a high impedance (3A
-10A) current source. The open-circuit voltage is less
than 10V.
3. A low-leakage MOSFET (<100nA) is recommended. A
pull-up resistor is not required, but may be necessary to
ensure that the Remote On/Off pin exceeds VIH(min)
(see Table 1).
Do not use a pull-up resistor to the +Vin
input, or drive the pin above VIH(max).
4. The PT4801 converter incorporates an “Under Voltage
Lockout” (UVLO) function. This function will overide
the Remote On/Off control until the input voltage
applied to ±Vin, is above the UVLO threshold. Consult
the data sheet specifications for the on/off input voltage
voltage thresholds.
5. Keep the on/off transition to less than 1ms. This prevents
erratic operation of the converter, whereby the output
voltage may drift un-regulated between 0V and the rated
output voltage during power-up.
Figure 1
Power-Up Sequence:
Turning Q1 in Figure 1 off, removes
the low-voltage signal at pin 1 and enables the outputs of
the PT4801 converter. After a delay of about 5ms, the
Vo1 output will begin to rise first. This is closely followed
by Vo2, and Vo3, which are internally sequenced to rise in
unison. The total power-up time is less than 25ms and is
relatively independent of load, and temperature. Figure 2
shows waveforms of all three output voltages, Vo1, Vo2,
and Vo3 following Q1 turning off. The turn off of Q1
corresponds to the fall in the applied Vgs. The wave-
forms were measured with a 48V input voltage.
Figure 2
PT4801
+V
IN
–V
IN
High =Off
+Vo
1
+Vo
2
+Vo
3
Co
1
Co
3
Co
2
C
IN
PT4801
6, 7
3, 4
10
14, 15
18
16, 17
1
Vo
1
COM
Vo
2
Vo
3
+V
IN
–V
IN
Remote
On/Off
Vo
2adj
Vo
3adj
12
19
11
Q
1
BSS138
COM
R
g
C
g s
R
g & C gs, See Note 6
Vo1 (5V/Div)
Vo2 (2V/Div)
Vo3 (2V/Div)
HORIZ SCALE: 5ms/Div
Q1 Vgs (5V/Div)
6. In Figure 1, Q1 is a low-threshold MOSFET. The
components Rg and Cgs are added to improve noise
immunity.
Application Notes
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