Datasheet

10 PA
C
RES
x 1.25V
t
RES
=
[sec]
R
S
L
O
V
IN(MAX)
x t
ON(MIN)
+
I
LIM_PK
=
V
CS(TH)
[A]
0
I
OUT
I
PP
f
SW
1
T=
LM25117
LM25117-Q1
www.ti.com SNVS714E –APRIL 2011–REVISED MARCH 2013
Figure 26. Inductor Current
During an output short condition, the worst case peak inductor current is limited to:
(12)
Where t
ON(MIN)
is the minimum HO on-time.
In most of cases, especially if the output voltage is relatively high, it is recommended that a soft-saturating
inductor such as a powder core device is used. If a sharp-saturating inductor is used, the inductor saturation
level must be above I
LIM_PK
. The temperatures of the NMOS devices, R
S
and inductor should be checked under
this output short condition.
Hiccup Mode Current Limiting
To further protect the regulator during prolonged current limit conditions, LM25117 provides a hiccup mode
current limit. An internal hiccup mode fault timer counts the PWM clock cycles during which cycle-by-cycle
current limiting occurs. When the hiccup mode fault timer detects 256 consecutive cycles of current limiting, an
internal restart timer forces the controller to enter a low power dissipation standby mode and starts sourcing
10μA current into the RES pin capacitor C
RES
. In this standby mode, HO and LO outputs are disabled and the
soft-start capacitor C
SS
is discharged.
C
RES
is connected from RES pin to AGND and determines the time (t
RES
) in which the LM25117 remains in the
standby before automatically restarting. When the RES pin voltage exceeds the 1.25V RES threshold, RES
capacitor is discharged and a soft-start sequence begins. t
RES
can be calculated from the following equation:
(13)
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