TLC5970
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SBVS140 –MARCH 2010
PRE-BOOST FUNCTION
The TLC5970 has a pre-boost function. This function increases the DAC code of the buck converter a few steps
from the 16th GS clock before the LED turns on to prevent the output voltage from decreasing much. The
pre-boost is finished at the 33rd GS clock rising edge. After the GS counter is reset, the first 16 GS clocks are
spent for the pre-boost and the LED is turned on from the 17th clock. Therefore, 4112 GS clocks are needed to
display the full GS data in the first period in auto repeat mode. In no auto repeat mode, 4112 GS clocks are
always needed for one display period.
UNDERVOLTAGE LOCKOUT (UVLO)
An undervoltage lockout (UVLO) circuit is implemented to keep the device disabled when VREG is lower than the
UVLO start voltage. The following list describes each functional block status during a UVLO condition:
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The buck converter control block, constant-current timing control, and oscillator are initialized.
The 40-bit data shift register is set to all '0'.
Each data latch is set to the default value except for the DC latch.
The data in the EEPROM is set to the DC data latch.
The power-supply source for the differential interface is connected to VCC.
FB voltage is discharged to GND.
NOISE REDUCTION
Large surge currents would flow through the IC and the board if all three LED channels are fully turned on
simultaneously at the start of each grayscale cycle. These large surge currents could introduce detrimental noise
and electromagnetic Interference (EMI) into other circuits. The TLC5970 turns on/off each OUTn with
approximately a 40-ns time difference to reduce the switching noise and LED anode voltage drop.
Copyright © 2010, Texas Instruments Incorporated
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