TLC5960DA datasheet(13/33 Pages) TI

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VADJ

0.6VTYP

REF

VREG5

On/Off

Control

Channel1

10%to100%

Dimming

Area

0.7

0.6

0.06

0.12

1.2

1.4

VADJ(V)

IfVADJ<1.4V,thenI

LED

VADJ/2

IfVADJ>1.4V,thenI

LED

0.6V

TLC5960

www.ti.com

SBVS147 – SEPTEMBER 2010

CONSTANT CURRENT CONTROL: PWM AND ANALOG DIMMING

The dedicated FET gate drivers help regulate the constant currents on the LED strings, as shown in Figure 15. A

sense resistor (RS) sets the constant current value on the corresponding LED channel. The gate driver regulates

this source node (Sn) voltage to be the same as the internal reference voltage (VREF). The default setting of VREF

is 0.6V. This internal reference voltage can be configured through the external input, VADJ. This function can be

used as a linear or analog dimming function for all LED strings simultaneously. As shown in Figure 16, the

TLC5960 uses halved VADJ input as the internal VREF. If VADJ is greater than 1.4V, the internal VREF falls back

to the typical 0.6V (100% analog dimming). Here, 1.4V is a positive-going threshold and is designed to have

100mV negative-going hysteresis as a noise margin. The VREF fallback mechanism is also applied in case VADJ

= open. The analog dimming linearity range is specified from 10% to 100%.

Figure 15. Constant Current Drive Amplifier

Figure 16. VADJ vs Internal Reference Voltage

The constant current value in the LED strings is set using the following equations:

(1)

(2)

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