TLC59401 Datasheet, PDF (15/29 Pages) Texas Instruments – 16-CHANNEL LED DRIVER WITH DOT CORRECTION AND GRAYSCALE PWM CONTROL

TLC59401
www.ti.com
SBVS137 – DECEMBER 2009
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 120 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.
See Figure 4 for 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 must 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: TLC59401 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 TLC59401 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 immediately 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
losing the first bit of GS data. 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. TLC59401 Operating Modes Truth Table
INPUT SHIFT REGISTER
192 bit
96 bit
OPERATING MODE
Grayscale PWM Mode
Dot Correction Data Input Mode
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): TLC59401
Submit Documentation Feedback
15