Datasheet

HICCUPt 25ms 4 145ms 4 680ms= · + · =
( )
ON OFF
12.5 V 7.5V
DISCHARGE VCC 10 F 145ms
346 A
ST
VCC VCC
t C
ICC
-
= · m =
m
-
= ·
( )
ON OFF
12.5 V 7.5V
CHARGE VCC 10 F 25ms
2mA
CHARGE
VCC VCC
t C
I
-
= · n =
-
= ·
VSD
2 60nA 2 60nA
OVER _ Load _ Detection _ Timer 12m sec
I 10 A
· ·
= = =
m
VSD
VSD
VCC 10V
I 10 A
R 1M
= = = m
W
HICCUP CHARGE DISCHARGEt t 4 t 4= · + ·
LM5023
www.ti.com SNVS961D –APRIL 2013–REVISED JANUARY 2014
Hiccup Mode
Hiccup Mode is a method to prevent the power supply from over-heating during and extended overload condition.
In an overload fault, the current limit comparator turns off the driver output on pulse-by-pulse basis. This starts
the Over Load Detection Timer, after the Over Load Detection Timer (OLDT) times out, the current limit
comparator is rechecked, if the power supply is still in an overload condition, the OUT drive is Latched-off and
VCC is allowed to drop to VCC
OFF
(7.5 V).
When VCC reaches VCC
OFF
, the VSD open drain output is disabled allowing the Depletion Mode start-up FET to
turn-on, charging up the VCC capacitor to VCC
ON
(12.5 V). When VCC reaches VCC
ON
, the VSD output goes
low turning-off the Depletion Mode FET. The VCC capacitor is discharged from VCC
ON
to VCC
OFF
at a rate
proportional to the VCC capacitor and the ICC
ST
current (346 µA typical). The charging and discharging of the
VCC capacitor is repeated four times (refer to Figure 15) so the total Hiccup time is:
After allowing VCC to charge and discharge four times, the LM5023 goes through an auto restart sequence,
enabling the LM5023 soft-start and driver output. It is important to set the Over Load Detection Timer long
enough so that under low input line and full load conditions that the power supply will have enough time to start-
up.
The Over Load Detection Timer can be set with the resister in series with the VSD pin ®
VSD
), refer to Figure 8.
Normally it is recommended that R
VSD
>1 MΩ, if a lower value is used then the standby power will be higher.
Assuming:
If the Depletion Mode FET charges the VCC capacitor with 2 mA,
VCC Capacitor is 10 uF.
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