MIC3263 datasheet(17/32 Pages) MICREL

17 / 32 page

Micrel, Inc.

MIC3263

VDD

January 2010

M9999-012110

This is the output of the internal LDO regulator. Connect a

c capacitor to this pin.

e DRC input

imming is a

feature of the MIC3263 which better matches the

sensitivity of the human eye compared to linear dimming.

The DRC

version is s

in T le 2

C Duty

ycle

Dimming Ratio

DR = 10

− 1) / 7

10μF cerami

PWM Dimming

The duty cycle of the PWM pulse applied to th

is converted to 16 log levels. This logarithmic d

unique

duty-cyc

to DR duty-cycle con

hown

(DR)

6.25

1.0

12.5

1.4

18.75

1.9

2.7

31.25

3.7

37.5

5.2

43.75

7.2

56.25

62.5

68.75

81.25

87.5

93.75

100

Table 2. Dimming Ratio

To avoid skipping between dimming levels, the

uses Flicker-Free Dimming control. This techniq

digital filter and hysteresis on the DRC pulse to

clean DR output. The digital filter has a 0.1μF capacitor on

the CINT pin to average the duty cycles of the PWM

pulses. The averaged duty cycle has to be 4.16% higher

than the nominal value before moving to the next dimming

level as shown in Figure 7. Likewise, to move the previous

dimming level the duty cycle has to be

−4.16% lower than

the nominal. To prevent flicker the duty-cycle hysteresis is

set a 2%.

MIC3263

ue uses a

provide a

Figure 7. Duty-Cycle Thresholds and Hysteresis

PWM Dimming Limits

The minimum pulse width of the PWM Dim is determined

by the PWM Dimming frequency and the L and C used in

the boost stages output filter. At low-PWM Dimming

frequencies, higher dimming ratios can be achieved:

TPWMD

Dim Ratio =

TLEDON

Figure 8. PWM Dimming Ratio

perceive light flicker at a

00Hz. At 100Hz the time

PWM dimming minimum

Consider that the human eye will

PWM dimming frequency below 1

between pulses is 10μs. If the

pulse width is 5μs, then:

10ms

Dim Ratio =

= 2000/1

5μs

If high dimming ratios are required, a lower dimming

frequency is required. During each DR pulse, the inductor

current has to ramp up to it steady state value to generate

the necessary boost output voltage in order for the full

programmed LED current to flow in the LED channels. The

smaller the inductance value the faster this time is and a

narrower PWM dimming pulse can be achieved. But

smaller inductance means higher ripple current.

MIC3263 Datasheet(PDF) 17 Page - Micrel Semiconductor

MIC3263 Datasheet(HTML) 17 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL