ADP8140ACPZ-2-R7 datasheet(16/23 Pages) AD

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ADP8140

Data Sheet

Rev. B | Page 16 of 23

Figure 27. Fault Flowchart

LED OPEN-CIRCUIT AND SHORT-CIRCUIT

PROTECTION

An LED open-circuit fault can result from a bad solder

connection or damaged LED. An open LED string results in the

current sink headroom falling to a very low level. The feedback

loop naturally interprets this as a request for more power. This

can quickly lead to a case where the output voltage is too high.

However, on the ADP8140, any abnormally high output voltage

is detected by the VO_SNS pin and the SINKx pins.

The VO_SNS pin senses the output voltage of the power supply

through an external resistor divider. VO_SNS is then compared

to an internal threshold (1.2 V typical). If the output voltage

rises such that the voltage of the VO_SNS pin is greater than

1.2 V, an output overvoltage fault (VOUT_OVP) is declared.

During a VOUT_OVP fault, any sinks with a voltage less than

80 mV (typical) are removed from the FB_OUT path. Then the

FB_OUT pull-down NMOS is released and

FAULTE

goes low,

causing the power stage to shut down. The LED current sinks

are left enabled during this event. When VO_SNS drops to

1.15 V (typical), the FB_OUT function resumes its normal

operation and

FAULTE

goes high.

Alternatively, the output voltage may not rise high enough to

trigger the VO_SNS pin, but it may rise high enough to cause

one of the SINKx pins to exceed 5.7 V (typical), or a shorted

LED may cause the SINKx pins to exceed this level. To prevent

excessive power dissipation and damage to the IC, when a

SINKx pin rises above 5.7 V (typical), a channel overvoltage

fault (CH_OVP) is declared. During a CH_OVP fault, any sinks

with a voltage less than 525 mV (typical) are removed from the

FB_OUT path. Then the FB_OUT pull-down NMOS is

released, causing the power stage to shut down. The LED

current sinks are left enabled during this event. When the

SINKx voltage drops to 4.5 V (typical), the FB_OUT function

resumes its normal operation.

Continued output overvoltage operation degrades efficiency

and can affect the lifetime of passive components. Therefore,

when an overvoltage condition is detected (either VOUT_OVP

or CH_OVP), then any open LED current sinks are identified

and removed from the feedback loop. But the sinks are always

SHUTDOWN

EN = LOW

EN = HIGH

SCALE ILED

DOWN

DIE TEMP

> 150°C

DIE TEMP

> 130°C

DIE TEMP

> 135°C

YES

ACTIVE

VT < MIN

(10µs NOISE

FILTER)

VO_SNS > 1.2V

(10µs NOISE

FILTER)

YES

REMOVE

SINKx FROM

MIN CIRCUIT

DIE TEMP PROTECTION

VT PROTECTION

YES

MAX(CHx)

> 5.5V?

YES

VOUT OVP

TURN POWER

STAGE OFF

(LEAVE ALL

SINKS ON)

YES

FAULT>1.2V

(10µs NOISE

FILTER)

FAULT>1.1V

(10µs NOISE

FILTER)

YES

FAULT DETECTION

VO_SNS

< 1.15V

ANY

ACTIVE CHx

< 550mV?

SET ALL SINKS TO

FULL ISET CURRENT

ISET

PROTECTION

YES

CHANNEL

OVERVOLTAGE

PROTECTION

YES

CHANNEL

CLAMPS

SET

FAULT

LOW

REMOVE

SINKx FROM

MIN CIRCUIT

SET ALL SINKS

TO 500mA

VT < MIN+

VMIN (HYS)

ANY SINK

< 75mV?

MAX(CHx)

< 4.5V

MAX(CHx)

< 13.8V?

MAX(CHx)

> 7.5V?

MAX(CHx)

> 15V

RSET

< 4.5kΩ

SET

FAULT

LOW

SET

FAULT

LOW

SET

FAULT

LOW

SET

FAULT

LOW

SET

FAULT

LOW

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