TLC5940_15 Datasheet, PDF (16/38 Pages) Texas Instruments – 16-Channel LED Driver

TLC5940
SLVS515D – DECEMBER 2004 – REVISED NOVEMBER 2015
www.ti.com
8.3.3 TEF: Thermal Error Flag
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), TEF becomes H and XERR pin
goes to low level. When the junction temperature becomes lower than the threshold temperature, TEF becomes
L and XERR pin becomes high impedance. TEF status can also be read out from the TLC5940 status register.
8.3.4 LOD: LED Open Detection
The TLC5940 has an LED-open detector that detects broken or disconnected LEDs. The LED open detector
pulls the XERR pin to GND when an open LED is detected. XERR and the corresponding error bit in the Status
Information Data is only active under the following open-LED conditions.
1. OUTn is on and the time tpd2 (1 μs typical) has passed.
2. The voltage of OUTn is < 0.3 V (typical)
The LOD status of each output can be also read out from the SOUT pin. See STATUS INFORMATION OUTPUT
section for details. The LOD error bits are latched into the Status Information Data when XLAT returns to a low
after a high. Therefore, the XLAT pin must be pulsed high then low while XERR is active in order to latch the
LOD error into the Status Information Data for subsequent reading via the serial shift register.
8.3.5 Delay Between Outputs
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 a 20-ns delay, and OUT2 has a 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.
8.3.6 Output Enable
All OUTn channels of the TLC5940 can be switched off with one signal. When BLANK is set high, all OUTn
channels are disabled, regardless of logic operations of the device. The grayscale counter is also reset. When
BLANK is set low, all OUTn channels work under normal conditions. If BLANK goes low and then back high
again in less than 300 ns, all outputs programmed to turn on still turn on for either the programmed number of
grayscale clocks, or the length of time that the BLANK signal was low, which ever is lower. For example, if all
outputs are programmed to turn on for 1 ms, but the BLANK signal is only low for 200 ns, all outputs still turn on
for 200 ns, even though some outputs are turning on after the BLANK signal has already gone high.
Table 2. BLANK Signal Truth Table
BLANK
LOW
HIGH
OUT0 - OUT15
Normal condition
Disabled
16
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