MIC3263YML datasheet(18/32 Pages) MICREL

18 / 32 page

Micrel, Inc.

MIC3263

January 2010

M9999-012110

M dimming

erefore the

ode. Ch2 is

m of all six ILED channels. Figure 9 shows the boost

converter is OFF (not switching) between PWM dimming

pulses.

Figure 9 shows the waveforms during PW

pulses. The DRC duty cycle is 75% and th

dimming ratio (DR) is 37%. Ch1 is the switch n

the su

)

D and use

ethod will

allows fo

Figure 9. PWM Dimming Pulses

(Ch1 Switch Node; Ch2 is the I

Tota

LED

Direct Dimming

For direct dimming control connect DFS to VD

the MODE pin for the dimming pulse. This m

bypass the internal dimming control and

dimming control by the external PWM Dimming ulse (see

Figure 9).

Figure 10. Direct Dimm

Boost Stage

A current-mode control is easi

voltage mode control, thus allow

ing Control

er to compensate than

ing for a less complex

control loop stability design. An error amplifier amplifies

the difference between the feedback voltage and the

voltage on the CRV capacitor. This amplified error signal is

called the VCONTROL. A PWM comparator compares the

output of the error amp (VCONTROL) to the sum of inductor

current and slope compensation currents. When the

current sums reach VCONTROL, the PWM pulse is terminated

and the boost power switch is turned off. A portion of the

energy stored in the inductor flows into the output

capacitor.

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