UC17131/2/3
UC27131/2/3
UC37131/2/3
APPLICATION INFORMATION
Choosing The CDEL Capacitor
ence an indeterminate state during this interruption, but
resume normal operation when VCC power returns to
normal.
The maximum amount of time that VCC power can be in-
terrupted and not require the outputs to go through a
turn-on delay cycle is user programmable by the CDEL
capacitor value. While VCC is interrupted, the outputs
will be in an indeterminate state and they may turn off
If the VCC power is interrupted for a time equal to or lon-
ger than t
then the following relationships apply.
D(OFF)
As the CDEL capacitor discharges past the V
FAULT_L
threshold, the output is fully disabled and must cycle
through a power up delay equal to t . The charge
current for the CDEL capacitor is equal to 4µA. The out-
during this interval, t . However, as long as the pro-
grammed interruption time is not exceeded, the outputs
will immediately turn back on with the return of VCC.
INT
D(ON)
puts will turn on when the CDEL capacitor charges up to
For example:
the V
threshold of 4.9V. The minimum turn-on
FAULT_H
tINT ≈ 500µs (User specified)
delay the outputs will experience will occur if t
is ex-
INT
actly equal to the t
has only discharged to V . This would be the mini-
FAULT_L
time and the CDEL capacitor
CDEL is selected such that the time it takes for this ca-
D(OFF)
pacitor to discharge from V
(5.8V) to V
CDEL_MAX
FAULT_L
mum turn-on delay time and is calculated with the follow-
ing equation:
(1.3V) with a discharge current of 94µA is just greater
than this t . This time is referred to as t
in Fig.
INT
D(OFF)
3b.
CDEL • VFAULT _L −VFAULT _H
tD ON
=
(
)
min
IDISCHARGE • tD
ICHARGE
OFF
(
)
CDEL =
VCDEL_MAX −VFAULT _L
Using the 10nF CDEL capacitor, for example, the mini-
mum turn-on delay calculates to 9ms. If the CDEL ca-
pacitor discharges completely to zero, then the 10nF
CDEL capacitor would cause a turn-on delay of 12.25ms.
The outputs would be off for this amount of time after
VCC power is restored. The total amount of time the out-
If t
is set equal to t , which the user has selected
D(OFF)
INT
to be 500µs, the minimum CDEL capacitor is calculated:
94µA • 500µs
CDEL =
5.8V − 1.3V
puts could be disabled is equal to the t
may include the indeterminate time of t
time, which
INT
For this application, the CDEL capacitor value calculates
to 10.4nF. By using a 10nF capacitor on CDEL, VCC can
be interrupted for up to 478µs and the outputs will experi-
, and the
D(OFF)
t
time, as shown in Fig. 3b.
D(ON)
VREF
VCC
7
6V
11
+ L
PRE-REGULATOR
ICC
RCSH
CREF
CSH
6
POWER
SUPPLY
LS
5
INPUT
COMPARATOR
IN 13
VREF
GND
72V
CCC
QOUT
HS
4
OUT
1/2
TURN-ON/OFF
AND SHORT
CIRCUIT
VREF
LOAD
CSL
3
PROTECTION
GND
2
– L
IGND
12
9
LED
10
HYST
CDEL
CCDEL
R HYST
UDG-98027
Figure 2a. High side application.
7
TI [ TEXAS INSTRUMENTS ]
