TLC5940 Datasheet, PDF (12/29 Pages) Texas Instruments – 16 CHANNEL LED DRIVER WITH DOT CORRECTION AND GRAYSCALE PWM CONTROL

TLC5940
SLVS515A – DECEMBER 2004 – REVISED AUGUST 2005
www.ti.com
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), the TEF circuit trips and pulls XERR
to ground. TEF status can also be read out from the TLC5940 status register.
LOD: LED OPEN DETECTION
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
2. When the voltage at OUTn is less than V_(LED) of 0.3 V (typical) (Note: the voltage at each OUTn is sampled
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.
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 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.
OUTPUT ENABLE
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
LOW
HIGH
OUT0 - OUT15
Normal condition
Disabled
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 1:
I
max
+
V(IREF)
R(IREF)
31.5
(1)
where:
V_(IREF) = 1.24 V
R_(IREF) = User selected external resistor.
Figure 3 shows the maximum output current I_O versus R_(IREF). R_(IREF) is the value of the resistor between IREF
terminal to GND, and I_O is the constant output current of OUT0 to OUT15.
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