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SLUS943A – MAY 2009 – REVISED JUNE 2009
power device. Once the soft start sequence starts, the input current is limited to the Over Current Protection
(OCP) threshold, I
O(OCP)
. If the input current through the IC attempts to exceed the OCP threshold, the switch Q1
is opened only enough to maintain the current at the OCP level. If the current limiting condition is maintained
longer than the deglitch time, t
DGL(OCP)
, both the switch Q1 and Q2 are opened completely, as shown in
In this fault case, the switch Q1 is turned off slowly, typically taking 100µS.
Once the OCP feature has been activated, the switch Q1 and Q2 will remain off for the OCP recovery time,
t
REC(OCP)
. Following this time the switch will turn on, using soft start sequence. If the current through the IC
remains below the OCP threshold, the switch will remain closed and normal operation resumes. If the current
through the IC attempts to exceed the OCP threshold again, the operation described above repeats.
I
ACIN
OCP
T hreshold
CHGIN
t
REC(OCP)
t
REC(OCP)
t
DGL(OCP)
t
DGL(OCP)
Figure 14. Charge Current OCP Timing Diagram
Battery Over-Voltage Protection
The battery over-voltage threshold, BV
OVP
, is internally set to 4.35V. If the battery voltage exceeds the BV
OVP
threshold, the FET Q1 and Q2 are turned off after a deglitch time of t
DGL(BOVP)
. The FET is turned on once the
battery voltage drops to BV
OVP
– V
HYS-BOVP
and remains below this threshold for t
REC(BOVP)
, as shown in
In this battery over-voltage fault case, Q1 is switched OFF gradually for a smooth transient response.
V
BAT
VBAT
OVP
CHGIN
t
DGL(BOVP)
t
REC(BOVP)
t
DGL(BOVP)
t
REC(BOVP)
Figure 15. Battery OVP Timing Diagram
Thermal Protection
If the junction temperature of the device exceeds T
J(OFF)
, the FET Q1 and Q2 are turned off. The FET is turned
back on when the junction temperature falls below T
J(OFF)
– T
J(OFF-HYS)
.
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