IfVADJ<1.4V,thenV

=

FOD

VADJ

4

(V)

IfVADJ>1.4V,thenV

=0.3V

FOD

Sn

VADJ

Failure

Recognition

Logic

Routine

ErrorDetection

Comparator

ComparisonVoltage:

FETShort=0.9Vtyp

FETOpen=0.3Vtyp

EN

V

LED

FETOpen

(FOD)

FETShort

(FSD)

TLC5960

www.ti.com

SBVS147 – SEPTEMBER 2010

FET OPEN DETECTION (FOD) AND FET SHORT DETECTION (FSD)

The TLC5960 monitors the source terminal of the FETs to detect any abnormal status of the external FETs, as

shown in Figure 22. In case a FET is open (FOD), the source node stays at a lower level, even if the TLC5960

drives the gate voltage higher and higher. To detect this error status, the default threshold is set to 0.3V. The

TLC5960 automatically adjusts the detection threshold internally, as described in Equation 6 and Equation 7,

depending on the analog dimming setting.

(6)

(7)

The FET short detection (FSD) detects overvoltage sensed at the source node. This failure mode usually implies

that the overcurrent is in the entire system and it may induce a critical situation because of potential

thermal-related issues. The TLC5960 always monitors the FSD threshold to keep the entire system safe. The

detection threshold is typically set at 0.9V.

In the case of FOD, the TLC5960 shuts off the failed LED string(s) and automatically separates the failed

string(s) from the operating strings. In the case of FSD, the TLC5960 normal function already shut off the failed

LED string(s), and then the TLC5960 delivers the failure notification signal through the XFLT output buffer. If the

failure phenomenon is removed, the FSD is automatically recovered, unlike LOD, LSD, and FOD, as shown in

Table 2.

Figure 22. TLC5960 Source Terminal Sensing to Protect FET Failure

Copyright © 2010, Texas Instruments Incorporated

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