PTB78560A_15 Datasheet, PDF (16/27 Pages) Texas Instruments – 30-W, 24-V/48-V INPUT DC/DC CONVERTERS WITH AUTO-TRACK™ SEQUENCING

PTB78560A, PTB78560B
PTB78560C
SLTS249 – JUNE 2005
www.ti.com
Negative Output Enable (Positive Inhibit)
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.
+V_I
1 = Outputs On
Q1
BSS138
-V_I
1
+V_I
DC/DC
Module
2
PEN
3
NEN
4 _-VI
Figure 24. Negative Enable Configuration
On/Off Enable Turn-On Time
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.
V_OBus (5 V/div)
I_I (1 A/div)
Q1 V_DS (5 V/div)
t − 5 ms/div
Figure 25. Output Enable Power-Up Characteristic
16
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