ADP8860ACPZ-R7 datasheet(21/52 Pages) AD

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ADP8860

Rev. 0 | Page 21 of 52

SCx_EN

Program all fade, on, and off timers before enabling any of the

LED current sinks. If ISCx is on during a blink cycle and

SCx_EN is cleared, it turns off (or fades to off if fade out is

enabled). If ISCx is off during a blink cycle and SCx_EN is

cleared, it stays off.

MAX

SCx

CURRENT

FADE-IN

FADE-OUT FADE-IN

FADE-OUT

ON TIME

OFF

TIME

OFF

TIME

SET BY USER

Figure 41. Independent Sink Blink Mode with Fading

SHORT-CIRCUIT PROTECTION MODE

The ADP8860 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 this SCP sensing is disabled

during both start-up and restart attempts (fault recovery). SCP

sensing reenables 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 simply 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 it 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 over-

voltage, the ADP8860 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

sufficient, or if the event happens too quickly, then the

ADP8860 enters overvoltage protection (OVP) mode when

VOUT exceeds the OVP threshold (typically 5.8 V). In the 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 step recurs, the process may

repeat. An interrupt flag is set at each OVP instance.

THERMAL SHUTDOWN/OVERTEMPERATURE

PROTECTION

If the die temperature of the ADP8860 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

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 42.

ADP8860ACPZ-R7 数据表(PDF) 21 Page - Analog Devices

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