TLC5945
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SLVS755–MARCH 2007
TEF: THERMAL ERROR FLAG
The TLC5945 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 TLC5945 status register.
LOD: LED OPEN DETECTION
The TLC5945 has an LED-open detection circuit that detects broken or disconnected LED's. 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 < 0.3V (typical)
The LOD status of each output can be also read out from the SOUT pin. See the 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.
OUTPUT ENABLE
All OUTn channels of the TLC5945 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 operate normally. If BLANK goes low and then back high before the
grayscale counter reaches 4095, all outputs turn on for their programmed number of grayscale clocks, or the
length of time the that the BLANK signal was low, whichever 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 turn on for 200 ns.
Table 3. BLANK Signal Truth Table
BLANK
LOW
OUT0 - OUT15
Normal condition
Disabled
HIGH
SETTING MAXIMUM CHANNEL CURRENT
The maximum output current per channel is programmed by a single resistor, R(IREF), which is placed between
IREF pin and GND pin. The voltage on IREF is set by an internal band gap V(IREF) with a typical value of
1.24 V. The maximum channel current is equivalent to the current flowing through R(IREF) multiplied by a factor of
31.5. The maximum output current can be calculated by Equation 6:
V
(IREF)
I
+
31.5
max
R
(IREF)
(6)
where:
V(IREF) = 1.24 V
R(IREF) = User-selected external resistor.
Imax must be set between 5 mA and 80 mA. The output current may be unstable if Imax is set lower than 5 mA.
Output currents lower than 5 mA can be achieved by setting Imax to 5 mA or higher and then using dot
correction.
Figure 3 shows the maximum output current IO versus R(IREF). R(IREF) is the value of the resistor between IREF
terminal to GND, and IO is the constant output current of OUT0 to OUT15. A variable power supply may be
connected to the IREF pin through a resistor to change the maximum output current per channel. The maximum
output current per channel is 31.5 times the current flowing out of the IREF pin.
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