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ADP8863
SHORT-CIRCUIT PROTECTION MODE
The ADP8863 can protect against short circuits on the output
(VOUT). Short-circuit protection (SCP) is activated at the point
when VOUT < 55% of V IN . Note that SCP sensing is disabled
during both startup and restart attempts (fault recovery). SCP
sensing is reenabled 4 ms (typical) after activation. During a
short-circuit fault, the device enters a low current consumption
state and an interrupt flag is set. The device can be restarted at any
time after receiving a short-circuit fault by rewriting nSTBY = 1.
It then repeats another complete soft start sequence. Note that
the value of the output capacitance (C OUT ) should be small
enough to allow VOUT to reach approximately 55% (typical) of
V IN within the 4 ms (typical) time. If C OUT is too large, the device
inadvertently enters short-circuit protection.
OVERVOLTAGE PROTECTION
Overvoltage protection (OVP) is implemented on the output.
There are two types of overvoltage events: normal (no fault) and
abnormal (from a fault or sudden load change).
Normal Overvoltage
In a normal (no fault) overvoltage, the output voltage approaches
V OUT(REG) (4.9 V typical) during normal operation. This is not
caused by a fault or load change, but is simply a consequence of
current sources and all other device functionality remain intact.
When the output voltage falls by about 500 mV (to 5.3 V
typical), the charge pump resumes operation. If the fault or load
event recurs, the process may repeat. An interrupt flag is set at
each OVP instance.
THERMAL SHUTDOWN/OVERTEMPERATURE
PROTECTION
If the die temperature of the ADP8863 rises above a safe limit
(150°C typical), the controllers enter thermal shutdown (TSD)
protection mode. In this mode, most of the internal functions
shut down, the part enters standby, and the TSD_INT interrupt
(Register 0x02) is set. When the die temperature decreases
below ~130°C, the part can be restarted. To restart the part,
remove it from standby. No interrupt is generated when the die
temperature falls below 130°C. However, if the software clears
the pending TSD_INT interrupt and the temperature remains
above 130°C, another interrupt is generated.
The complete state machine for these faults (SCP, OVP, and
TSD) is shown in Figure 47.
INTERRUPTS
There are five interrupt sources available on the ADP8863 in
Register 0x02.
the input voltage times the gain reaching the same level as the
clamped output voltage (V OUT(REG) ). To prevent this type of
overvoltage, the ADP8863 detects when the output voltage rises
to V OUT(REG) . It then increases the effective R OUT of the gain stage
to reduce the voltage that is delivered. This effectively regulates
V OUT to V OUT(REG) ; however, there is a limit to the effect that this
system can have on regulating V OUT . It is designed only for
normal operation and it is not intended to protect against faults
or sudden load changes. When the output voltage is regulated to
V OUT(REG) , no interrupt is set and the operation is transparent to
the LEDs and the overall application.
Abnormal Overvoltage
Because of the open-loop behavior of the charge pump as well
as how the gain transitions are computed, a sudden load change
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Main light sensor comparator: The CMP_INT interrupt
sets every time the main light sensor comparator detects a
threshold (L2 or L3) transition (rising or falling condition).
Sensor Comparator 2: The CMP2_INT interrupt works
the same way as CMP_INT, except that the sensing input
derives from the second light sensor. The programmable
thresh-olds are the same as for the main light sensor
comparator.
Overvoltage protection: OVP_INT is generated when the
output voltage exceeds 5.8 V (typical).
Thermal shutdown circuit: an interrupt (TSD_INT) is
generated when entering overtemperature protection.
Short-circuit detection: SHORT_INT is generated when
the device enters short-circuit protection mode.
or fault can abnormally force V OUT beyond 6 V. This causes an
abnormal overvoltage situation. If the event happens slowly
enough, the system first tries to regulate the output to 4.9 V as
in a normal overvoltage scenario. However, if this is not suffi-
cient, or if the event happens too quickly, the ADP8863 enters
overvoltage protection (OVP) mode when V OUT exceeds the
The interrupt (if any) that appears on the nINT pin is deter-
mined by the bits mapped in Register INTR_EN (0x03). To
clear an interrupt, write a 1 to the interrupt in the MDCR2
register (0x02) or reset the part. Reading the interrupt, or writing a
0, has no effect.
OVP threshold (typically 5.8 V). In OVP mode, only the charge
pump is disabled to prevent V OUT from rising too high. The
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