Microchip MIC3263YML Manual

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Side 1/8

MIC3263 Evaluation Board

Six-Channel WLED Driver for

Backlighting Applications with

Flicker-Free Dimming

Bringing the Power to Light™

MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

March 2010 M9999-032410-B

General Description

This evaluation board (EVB) is designed for the MIC3263.

The MIC3263 is a high-efficiency Pulse Width Modulation

(PWM) boost switching regulator that is optimized for

constant-current WLED driver backlighting applications.

The MIC3263 drives six channels of up to ten low-power

WLEDs per channel. Each channel is matched in current

to within ±3% for constant brightness across the screen

and can be programmed from 15mA to 30mA.

The MIC3263 provides a very flexible dimming control

scheme with high accuracy and noise immunity. The

dimming frequency can be set to any value between

100Hz and 20kHz by an external resistor. The dimming

ratio is determined by the duty-cycle of a dimming ratio

control input signal and can be set to one of 16 levels with

a minimum ratio of 1%. The LED dimming current is set by

an external resistor to allow programming of LED current

between 15mA and 30mA.

The dimming ratio of the MIC3263 is fixed to 16

logarithmic levels to better match the sensitivity of the

human eye. Each of the dimming levels has hysteresis to

avoid skipping between levels resulting in Flicker-Free

operation.

The MIC3263 has a programmable PWM switching

frequency from 400kHz to 1.8MHz to allow small inductor

sizes. The 6V to 40V wide-input voltage range of MIC3263

allows direct operation from 6V or high cell count Li-Ion

batteries commonly found in notebook computers.

Precautions

The MIC3263 evaluation board operates as a boost

converter, which requires the output voltage to be greater

than the input voltage. Connect a PWM dimming signal to

the DRC pin. The DRC pin needs an input signal to

operate.

Requirements

1. Voltage source capable of supplying 10W

2. Load: Six LED strings

3. Scope

4. Function generator for PWM Dimming

Getting Started

1. Set the LED current of all six channels by one resistor

RISET (noted as R9 on the EVB). Use 2kΩ for 30mA

and 3kΩ for 20mA. Use the following equation to find

RISET:

LED

R =

ISET I

Ω

2. Connect six strings of LEDs from LED out to LED-

RTN. Each one of the six LED strings needs to

connect to one of the LED RTN. The cathode end of

each LED string connects to one of the six LED RTN

pins. The anode end of all the LED strings connects to

LED OUT (VOUT). The number of LEDs in each string

should be from 4 to 10.

3. Connect 12V (or other input voltage) to VIN and GND.

4. Use a current probe to measure the load current and

monitor the switch node with a scope to view the

switching waveform

5. PWM Dimming:

a. Connect a function generator to the

dimming input (DRC pin) 0V to 5V at

100Hz to 40kHz.

b. Adjust the duty-cycle of the function

generator for PWM dimming. The

MIC3263 converts the duty-cycle at the

DRC to one of sixteen dimming ratios

(DR) according to Table 1.

c. Follow the power-on sequence to ensure

all channels turn on.

d. The EVB is set for 30mA LED current. For

a different LED current, change R9 using

the given equation.

Micrel, Inc. MIC3263 Evaluation Board

March 2010 2 M9999-032410-B

Power-On Sequence

VIN needs to be present before PWM pulses are applied

to the DRC pin. Some channels may not turn on if the

power-on sequence is not followed. This may be the

case if the circuits that monitor the IO pins see transients

during the turn on-time and may interpret voltage spikes

during turn-on as a fault, preventing that channel from

turning on. When a channel is off, its IO pin is at high

impedance.

It is best to follow the sequence:

1. VIN

2. PWM dimming at DRC

3. Enable high

MODE

This selects the internal PWM dimming frequency range.

When MODE is low, the PWM dimming frequency range

is 100Hz to 2kHz and it selects low-frequency (LF)

mode. When MODE is high, the PWMD frequency range

is 1.5kHz to 20kHz and it selects high-frequency (HF)

mode.

DFS

DFS stands for Dimming Frequency Select. The

dimming frequency of the LEDs is different than the input

dimming frequency at the DRC input. The MIC3263 uses

an internal dimming frequency. This internal dimming

frequency is programmable by an external resistor to

ground RDFS (R8).

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.

Use the following equations to determine the value for

RDFS:

RDFS(kΩ) = −20 × fDIM(kHz) + 432 (HF Mode)

RDFS(kΩ) = −335 × fDIM(kHz) + 433 (LF Mode)

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.

OVP

This is the over-voltage protection monitor. Also this is

the feedback signal that connects to the error amplifier

input. The output voltage that the OVP will trigger is set

according to the following equation. Using the values for

this example gives a max output voltage of:

VOVP = 2.4 × (R1+R2)/R1 = 38V

Internal PWM Dimming

The duty-cycle of the PWM pulse applied to the DRC

input is converted to 16 log levels. This logarithmic

dimming is a unique feature of the MIC3263 which better

matches the sensitivity of the human eye compared to

linear dimming. The DRC duty-cycle to DR duty-cycle

conversion is shown in Table 2.

DRC Duty

Cycle

PWM Dimming Ratio (DR)

DR = 10(N −

−

−− 1) / 7

%% %

0 0 0

1 6.25 1.0

2 12.5 1.4

3 18.75 1.9

4 25 2.7

5 31.25 3.7

6 37.5 5.2

7 43.75 7.2

8 50 10

9 56.25 14

10 62.5 19

11 68.75 27

12 75 37

13 81.25 52

14 87.5 72

15 93.75 100

Table 1. Dimming Ratio

Ordering Information

Order Part Number Description

MIC3263YML EV Boost Evaluation Board

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	MIC3263YML

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