ADP8863ACPZ-R7 datasheet(21/48 Pages) AD

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ADP8863

Rev. 0 | Page 21 of 48

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 VIN. 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 (COUT) should be small

enough to allow VOUT to reach approximately 55% (typical) of

VIN within the 4 ms (typical) time. If COUT 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

VOUT(REG) (4.9 V typical) during normal operation. This is not

caused by a fault or load change, but is simply a consequence of

the input voltage times the gain reaching the same level as the

clamped output voltage (VOUT(REG)). To prevent this type of

overvoltage, the ADP8863 detects when the output voltage rises

to VOUT(REG). It then increases the effective ROUT of the gain stage

to reduce the voltage that is delivered. This effectively regulates

VOUT to VOUT(REG); however, there is a limit to the effect that this

system can have on regulating VOUT. 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

VOUT(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 VOUT 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 VOUT exceeds the

OVP threshold (typically 5.8 V). In OVP mode, only the charge

pump is disabled to prevent VOUT 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 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 46.

INTERRUPTS

There are five interrupt sources available on the ADP8863 in

•

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.

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

0, has no effect.

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