´

ISETH

FB

ISET

ISETH

V

I

=

K

R

8

DIM

FPWM

1.818

10

F

=

R

´

TPS61183

www.ti.com

SLVSAB4A – JUNE 2010 – REVISED JULY 2010

LED CURRENT SINKS

The six current sink regulators embedded in the TPS61183 can be collectively configured to provide up to a

maximum of 30 mA each. These six specialized current sinks are accurate to within ±2% max for currents at 20

mA, with a string-to-string difference of ±1.5% typical.

The IFB current must be programmed to the highest WLED current expected using the ISETH pin resistor and

Equation 2.

(2)

Where:

ENABLE AND STARTUP

allows the IC to start when EN is tied to the VDDIO pin; however, VDDIO does not come to full regulation until

EN is high. The TPS61183 checks the status of all current feedback channels and shuts down any unused

feedback channels. It is recommended to short the unused channels to ground for faster startup.

After the device is enabled, if the PWMIN pin is left floating, the output voltage of the TPS61183 regulates to the

minimum output voltage. Once the IC detects a voltage on the PWMIN pin, the TPS61183 begins to regulate the

IFB pin current, as pre-set per the ISETH pin resistor, according to the duty cycle of the signal on the PWMIN

pin. The boost converter output voltage rises to the appropriate level to accommodate the sum of the white LED

string with the highest forward voltage drops plus the headroom of the current sink at that current.

Pulling the EN pin low shuts down the IC, resulting in the IC consuming less than 11 µA in shutdown mode.

IFB PIN UNUSED

The TPS61183 has open/short string detection. For an unused IFB string, simply short it to ground or leave it

open. Shorting unused IFB pins to ground for faster startup is recommended.

BRIGHTNESS DIMMING CONTROL

The TPS61183 has programmable PWM dimming control with the PWM control interface.

The internal decoder block detects duty cycle information from the input PWM signal, saves it in an eight bit

register and delivers it to the output PWM dimming control circuit. The output PWM dimming control circuit turns

on/off six output current sinks at the PWM frequency set by RFPWM and the duty cycle from the decoder block.

The TPS61183 also has direct PWM dimming control with the PWM control interface. In direct PWM mode, each

current sink turns on/off at the same frequency and duty cycle as the input PWM signal. See the Mode Selection

section for dimming mode selection.

When in programmable PWM mode, it is recommended to insert a series resistor of 10k

Ω to 20kΩ value close to

PWMIN pin. This resistor together with an internal capacitor forms a low pass R-C filter with 30ns to 60ns time

constant. This prevents possible high frequency noises being coupled into the input PWM signal and causing

interference to the internal duty cycle decoding circuit. However, it is not necessary for direct PWM mode since

the duty cycle decoding circuit is disabled during the direct PWM mode.

ADJUSTABLE PWM DIMMING FREQUENCY AND MODE SELECTION (R_FPWM / MODE)

The TPS61183 can operate in programmable mode or direct PWM mode. Tying the RFPWM/MODE pin to

VDDIO forces the IC to operate in direct PWM mode. Alternatively, a resistor between the RFPWM/MODE pin

and ground sets the IC into programmable mode with the value of the resistor determines the PWM dimming

frequency. Use Equation 3 or refer to Table 2 to select the correct value:

(3)

Copyright © 2010, Texas Instruments Incorporated

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