Microchip MIC2297-42YML Manual

Microchip Ikke kategoriseret MIC2297-42YML

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Side 1/6

MIC2297 Evaluation Board

600kHz 42V OVP PWM White LED Driver

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

May 2008 M9999-053008-A

General Description

The MIC2297 is a 600kHz PWM White LED Driver

optimized for 6 to 10 series WLEDs. With an output

voltage of up to 42V and a guaranteed 1.2A on the internal

power switch, the MIC2297 can easily drive 10 WLEDs at

20mA continuous current. The MIC2297 features WLED

brightness control using the BRT pin and has output over

voltage protection (OVP) to protect the device in case the

WLEDs are disconnected unexpectedly. Available in a tiny

10-pin 2.5mm x 2.5mm x 0.85mm MLF

package, the

MIC2297 solution only requires a total of 6 external

components.

The MIC2297 operates at a default (BRT pin is open)

feedback voltage of only 200mV. The low feedback

voltage reduces the power dissipation from the external

current set resistor and increases total operating

efficiency.

When brightness control is required, the MIC2297 features

brightness control by applying a DC voltage to the BRT

pin. When applying a DC voltage to the BRT pin, the

feedback voltage is equal to the BRT voltage divided by 5.

This feature essentially increases or decreases the

feedback voltage from its default value (200mV), changing

the WLED current to control the WLED brightness.

Alternatively, a PWM signal may also be applied to the

BRT pin for brightness control. When a PWM signal (1kHz

recommended) is applied to the BRT pin, the WLEDs are

dimmed depending on the duty cycle and the peak voltage

of the signal. The PWM frequency can range from 1kHz to

1MHz. The selected PWM frequency does not affect the

WLED brightness. Assuming a 1V PWM signal is applied,

as the duty cycle decreases, the feedback voltage

decreases, thus reducing the WLED current.

Requirements

The MIC2297 evaluation board requires an input power

source that is capable of delivering greater than 1.2A at

2.5V.

Precautions

The evaluation board does not have reverse polarity

protection. Applying a negative voltage to the V

terminal

may damage the device.

The MIC2297 evaluation board is tailored for a single or

dual Li-Ion input source. The input voltage should never

exceed 10V.

Getting Started

1. Connect an external supply to V

. Apply desired

input voltage to the V

(J1) and ground (J4)

terminals of the evaluation board, paying careful

attention to polarity and supply voltage (2.5V ≤ V

≤ 10V). An ammeter may be placed between the

input supply and the V

(J1) terminal to the

evaluation board to accurately monitor the input

current. The ammeter and/or power lead

resistance can reduce the voltage supplied to the

input; therefore, the supply voltage at the V

(J1)

terminal should be monitored.

2. Enable/Disable the MIC2297. To enable the

MIC2297, apply a 1.5V or greater voltage signal to

the EN (J2) terminal. To disable the device, pull

the EN (J2) pin below 0.4V. The evaluation board

is configured with a jumper (JP1) from V

to the

enable pin and a 10k pull-down resistor to ground

to conveniently turn the part on or off. Connecting

the jumper (JP1) will enable the MIC2297, while

removing the jumper will disable the part.

3. DCV Brightness Control. To control the

brightness with a DC voltage, see the DVC

Brightness Control section.

4. PWM Brightness Control. To control the

brightness with a PWM Signal, see the PWM

Brightness Control section.

Note: For detailed specifications, please refer to the

MIC2297 Datasheet at www.micrel.com.

Ordering Information

Part Number Description

MIC2297-42YML EV Evaluation board with the

MIC2297 42V device

Micrel, Inc. MIC2297 Evaluation Board

May 2008

2 M9999-053008-A

LED Current Setting

There are 10 WLEDs provided with the evaluation board.

Two of the WLEDs (D1 and D2) may be by-passed by

placing a jumper on JP3. The WLED current (I

LED

) is equal

to the feedback voltage (V

= 200mV by default) divided

by the R3 resistance value. The evaluation board is

provided with R3 equal to 10Ω. The brightness level is

proportional to I

LED

. Programming the feedback voltage

changes the I

LED

, therefore changing the brightness level.

LED

= V

/ R3 (1)

DCV Brightness Control

The brightness level can be set by applying a DC voltage

(BRT) to the BRT pin. When a DC voltage is applied to the

BRT pin, the feedback voltage is changed from the default

value of 200mV to:

= BRT / 5 (2)

Assuming BRT equals 1V, then V

will be 200mV and

ILED may be calculated by:

LED

= V

/ R3

LED

= 200mV / 10Ω

LED

= 20mA

Similarly, if BRT equals 2V, then V

will be 400mV and

the I

LED

may be calculated by:

LED

= V

/ R3

LED

= 400mV / 10Ω

LED

= 40mA

The feedback voltage can be changed using the BRT pin.

Changing the feedback voltage changes the WLED

current, which will change the WLED brightness. Refer to

the Figure 1 and Figure 2 for reference.

(DC Coupled)

(50mV/div)

Feedback Volta

TIME (400µs/div)

Volta

(DC Coupled)

(1V/div)

Figure 1. BRT = 1V, V

= 200mV, I

LED

= 20mA

(DC Coupled)

(100mV/div)

Feedbac

Volta

TIME (400µs/div)

Volta

(DC Coupled)

(1V/div)

Figure 2. BRT = 2V, V

= 400mV, I

LED

= 40mA

PWM Brightness Control

The brightness level can also be set by applying a PWM

signal to the BRT pin. To calculate the feedback voltage

when a PWM signal is applied to the BRT pin, use the

following formula:

FB = VPEAK / 5 * D (3)

VPEAK is the peak of the PWM voltage and D is the duty

cycle. If VPEAK is 1V and the duty cycle is 1%, then VFB can

be calculated by:

VFB = 1V / 5 * 0.01

VFB = 2mV

The ILED can then be calculated by:

ILED = VFB / R3

ILED = 2mV / 10Ω

ILED = 200µA

Similarly, if the VPEAK is 1V and the duty cycle is 50%, then

VFB can be calculated by:

VFB = 1V / 5 * 0.5

VFB = 100mV

The ILED can then be calculated by:

ILED = VFB / R3

ILED = 100mV / 10Ω

ILED = 10mA

With PWM brightness control, the MIC2297 has great

versatility since brightness may be set anywhere from 0 to

100 percent. Refer to the following figures for reference.

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	MIC2297-42YML

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