Datasheet
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Negative Output Enable (Positive Inhibit)
DC/DC
Module
PEN
NEN
2
3
4
1
+V
I
-V
I
+V
I
-V
I
1=OutputsOn
Q1
BSS138
On/Off Enable Turn-On Time
t − 5 ms/div
Q1 V
DS
(5 V/div)
I
I
(1 A/div)
V
O
Bus (5 V/div)
PTB78560A , PTB78560B
PTB78560C
SLTS249 – JUNE 2005
To configure the converter for a negative enable function, PEN (pin 2) is left open circuit, and the system On/Off
control signal is applied to NEN (pin 3). A low-level control signal (less than 0.8 V) must then be applied to pin 3
to enable an output from the converter. An example of this configuration is detailed in Figure 24 .
Figure 24. Negative Enable Configuration
Once enabled, the converter executes a soft-start power up. The converter exibits a short delay of approximately
7 ms, measured from the transition of the enable signal to the instance the V
O
Bus output begins to rise. The
output is in regulation within 20 ms.
Figure 25. Output Enable Power-Up Characteristic
16
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