www.ti.com

TEF: THERMAL ERROR FLAG

LOD: LED OPEN DETECTION

DELAY BETWEEN OUTPUTS

OUTPUT ENABLE

SETTING MAXIMUM CHANNEL CURRENT

Imax +

V

(IREF)

R

(IREF)

31.5

(1)

TLC5940

SLVS515A – DECEMBER 2004 – REVISED AUGUST 2005

The TLC5940 provides a temperature error flag (TEF) circuit to indicate an overtemperature condition of the IC. If

the junction temperature exceeds the threshold temperature (160

°C typical), the TEF circuit trips and pulls XERR

to ground. TEF status can also be read out from the TLC5940 status register.

The TLC5940 provides an LED open-detection circuit (LOD). This circuit reports an error if any one of the 16

LEDs is open or disconnected from the circuit. The LOD circuit trips when the following two conditions are met

simultaneously:

1. BLANK is set to LOW

1

µs after being turned on).

The LOD circuit also pulls XERR to GND when tripped. The LOD status of each channel can also be read out

from the TLC5940 status information data (SID) in GS data input cycle.

The TLC5940 has graduated delay circuits between outputs. These circuits can be found in the constant current

driver block of the device (see the functional block diagram). The fixed-delay time is 20 ns (typical), OUT0 has no

delay, OUT1 has 20 ns delay, and OUT2 has 40 ns delay, etc. The maximum delay is 300 ns from OUT0 to

OUT15. The delay works during switch on and switch off of each output channel. These delays prevent large

inrush currents which reduces the bypass capacitors when the outputs turn on.

All OUTn channels of TLC5940 can switched off with one signal. When BLANK is set to high, all OUTn are

disabled, regardless of logic operations of the device. The grayscale counter is also reset. When BLANK is set to

low, all OUTn work under normal conditions.

Table 2. BLANK Signal Truth Table

BLANK

OUT0 - OUT15

LOW

Normal condition

HIGH

Disabled

where:

12