Datasheet

Data Sheet ADP8861
Rev. B | Page 17 of 40
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 it is simply a consequence
of the input voltage times the gain reaching the same level as the
clamped output voltage (V
OUT(REG)
). To prevent this type of overvol-
tage, the ADP8861 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
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 sufficient,
or if the event happens too quickly, then the ADP8861 enters
OVP mode when V
OUT
exceeds the OVP threshold (typically
5.8 V). In OVP mode, only the charge pump is disabled to
prevent V
OUT
from rising too high. The 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 ADP8861 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,
simply 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 38.
INTERRUPTS
There are three interrupt sources available on the ADP8861 in
Register 0x02.
• Overvoltage protection: The OVP_INT interrupt 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.
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.