MIC3263 datasheet(15/32 Pages) MICREL

15 / 32 page

Micrel, Inc.

MIC3263

January 2010

M9999-012110

Descriptions

t a resi

GND to set the switching frequency between

400kHz and

llowing equation

RFSW

p logy and

s is a virtual ground of the resistor divider feedback

ch connects

switch

will open and disconnects the feedback resistor network

IN by the

his is the

hat connects to the error amp input.

ency range.

cy range is

D frequency

elects High

elects Low

Use the following equations to determine the value for

(kHz)

+ 432 (HF Mode)

(kHz)

+ 433 (LF Mode)

For a dimming frequency of 10kHz, use the HF Mode:

432

= 232kΩ in HF Mode

se LF Mode:

(kΩ) =

−335 × 1 + 433 = 98kΩ in LF Mode

Use the closest standard value.

Figure 5. RDFS vs. Dimming Frequency in HF Mode

Figure 6. RDFS vs. Dimming Frequency in LF Mode

FSW

Sets the boost switching frequency. Connec

from FSW to

stor

RDFS(kΩ) = −20 × fDIM

1.8MHz. Use the fo

s to sele

RFSW (kΩ) ≈ 500 − 0.3 × fSW(kHz)

RSL

The boost section is a peak current mode ty

needs slope compensation to eliminate s

oscillation (see “Slope Compensation”).

OVPS

RDFS(kΩ) = −20 × 10 +

-harmonic

For 1kHz, u

Thi

network in the boost stage. At turn on, a swit

this node-to-ground. When the part is disabled the

from ground. This eliminates current draw from V

boost resistor divider network.

OVP

This is the over-voltage protection monitor. Also

feedback signal t

MODE

This selects the internal PWM dimming frequ

When mode is low the PWM dimming frequen

100Hz to 2kHz. When mode is high the PWM

range is 1.5kHz to 20kHz. Mode is high s

Frequency (HF) mode; Mode is low s

Frequency (LF) mode.

DFS

DFS stands for Dimming Frequency Select. T

frequenc

he dimming

y of the LEDs is different than the input dimmin

frequency at the DRC input. The MIC3263 uses n in

dimming frequency. This internal dimming frequency is

programmable by an external resistor to ground RDFS.

For direct dimming control, connect DFS to VDD and use

the MODE pin for the input dimming pulse. This method by

passes the internal dimming control and allows for

dimming control by the external PWM pulse.

When using internal dimming the range is determined by

the MODE pin and the actual frequency is determined by

RDFS. Connect a resistor to ground to select a dimming

frequency.

ternal

RDFS:

RDFS(kΩ) = −335 × fDIM

Example:

DFS

RDFS(in kΩ) = -20*Dimming Frequency (in kHz) + 432

100

150

200

250

300

350

400

450

2.5

7.5

12.5

17.5

22.5

Dimming Frequency (kHz)

RDFS(kΩ) = -335*Dim ming Frequency (in kHz) + 433

100

200

300

400

500

0.2

0.4

0.6

0.8

1.2

1.4

Dimming Frequency (kHz)

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