3.0

5.5

4.5

5.5

TPS68401, TPS68402

www.ti.com

SLVSA68A – MARCH 2010 – REVISED JANUARY 2011

Figure 2. Charge Pump Output Voltage

LED DRIVER OPERATIONAL DESCRIPTION

The TPS68401/TPS68402 has three independent constant current LED drivers with 8-bit PWM control. Output

duty cycle is controlled either by program instructions or R/G/B PWM registers. Green and blue channels are

when driving LEDs with low VF or the supply voltage is high enough to drive a LED with high VF.

PWM frequency is either 256 Hz or 558 Hz and is selected through PWM_HF bit in the CONFIG register. Linear

and logarithmic PWM duty-cycle-to-input response is selectable through the LOG_EN bit of the ENABLE register.

LOG_EN bit controls PWM response for all three channels. Logarithmic response is approximated by

piece-wise-linear function as shown below.

When the external clock source is selected for driving the PWM, PWM frequency scales with the external clock

frequency. Nominal 256-Hz PWM frequency requires external clock frequency of 32.768 kHz.

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