TLC5941-Q1 Datasheet, PDF (15/27 Pages) Texas Instruments – 16-CHANNEL LED DRIVER WITH DOT CORRECTION AND GRAYSCALE PWM CONTROL

TLC5941-Q1
www.ti.com ........................................................................................................................................................................................... SLDS165 – DECEMBER 2008
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:
Imax
+
V(IREF)
R(IREF)
31.5
(6)
where:
V_(IREF) = 1.24 V
R_(IREF) = User-selected external resistor.
I_max must be set between 5 mA and 60 mA. The output current may be unstable if I_max is set lower than 5 mA.
Output currents lower than 5 mA can be achieved by setting I_max to 5 mA or higher and then using dot correction.
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. 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.
POWER DISSIPATION CALCULATION
The device power dissipation needs to be below the power dissipation rate of the device package to ensure
correct operation. Equation 7 calculates the power dissipation of device:
ǒ Ǔ ǒ Ǔ PD + VCC
ICC ) VOUT
IMAX
N
DCn
63
dPWM
(7)
where:
V_CC: device supply voltage
I_CC: device supply current
V_OUT: TLC5941 OUTn voltage when driving LED current
I_MAX: LED current adjusted by R_(IREF) Resistor
DC_n: maximum dot correction value for OUTn
N: number of OUTn driving LED at the same time
d_PWM: duty cycle defined by BLANK pin or GS PWM value
OPERATING MODES
The TLC5941 has two operating modes defined by MODE as shown in Table 4. The GS and DC registers are
set to random values that are not known just after power on. The GS and DC values must be programmed
before turning on the outputs. Please note that when initially setting GS and DC data after power on, the GS data
must be set before the DC data is set. Failure to set GS data before DC data may result in the first bit of GS data
being lost. XLAT must be low when the MODE pin goes high-to-low or low-to-high to change back and forth
between GS mode and DC mode.
MODE
GND
V_CC
Table 4. TLC5941 Operating Modes Truth Table
INPUT SHIFT REGISTER
192 bit
96 bit
OPERATING MODE
Grayscale PWM Mode
Dot Correction Data Input Mode
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): TLC5941-Q1
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