MIC2297-42YML-EV

MIC2297 Evaluation Board 600kHz 42V OVP PWM White LED Driver 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 VIN 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 VIN. Apply desired input voltage to the VIN (J1) and ground (J4) terminals of the evaluation board, paying careful attention to polarity and supply voltage (2.5V ≤ VIN ≤ 10V). An ammeter may be placed between the input supply and the VIN (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 VIN (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 VIN 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 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 Micrel, Inc. MIC2297 Evaluation Board BRT Voltage (DC Coupled) (1V/div) Feedback Voltage (DC Coupled) (50mV/div) BRT Voltage (DC Coupled) (1V/div) 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: VFB = BRT / 5 (2) Assuming BRT equals 1V, then VFB will be 200mV and ILED may be calculated by: ILED = VFB / R3 ILED = 200mV / 10Ω ILED = 20mA Similarly, if BRT equals 2V, then VFB will be 400mV and the ILED may be calculated by: ILED = VFB / R3 ILED = 400mV / 10Ω ILED = 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. Feedback Voltage (DC Coupled) (100mV/div) 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 (ILED) is equal to the feedback voltage (VFB = 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 ILED. Programming the feedback voltage changes the ILED, therefore changing the brightness level. ILED = VFB / R3 (1) TIME (400µs/div) Figure 2. BRT = 2V, VFB = 400mV, ILED = 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: VFB = 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. TIME (400µs/div) Figure 1. BRT = 1V, VFB = 200mV, ILED = 20mA May 2008 2 M9999-053008-A MIC2297 Evaluation Board BRT Voltage (DC Coupled) (1V/div) BRT Voltage (DC Coupled) (1V/div) Feedback Voltage (DC Coupled) (10mV/div) Feedback Voltage (DC Coupled) (50mV/div) Micrel, Inc. TIME (400µs/div) TIME (400µs/div) Figure 3. Duty Cycle = 1%, VFB = 2mV, ILED = 200µA Figure 6. Duty Cycle = 80%, VFB = 160mV, ILED = 16mA Feedback Voltage (DC Coupled) (50mV/div) BRT Voltage (DC Coupled) (1V/div) Feedback Voltage (DC Coupled) (50mV/div) In Figure 7, when the duty cycle is equal to 100%, D equals 1. When we set D equal to 1 in equation (3), notice (3) becomes the same as equation (2), if we assume VPEAK equals BRT. Using a 100% duty cycle is the same as applying a constant DC voltage to the BRT pin. In this instance, Figure 7 is exactly the same as Figure 1. TIME (400µs/div) BRT Voltage (DC Coupled) (1V/div) Figure 4. Duty Cycle = 20%, VFB = 40mV, ILED = 4mA TIME (400µs/div) BRT Voltage (DC Coupled) (1V/div) Feedback Voltage (DC Coupled) (50mV/div) Figure 7. Duty Cycle = 100%, VFB = 200mV, ILED = 20mA TIME (400µs/div) Figure 5. Duty Cycle = 50%, VFB = 100mV, ILED = 10mA May 2008 3 M9999-053008-A Micrel, Inc. MIC2297 Evaluation Board Typical Application Circuit L1 22µH J1 VIN DS1 JP2 U1 MIC2297-42YML 3 JP3 SW VIN JP1 J2 EN 4 R1 10k J3 BRT 1-Cell Li Ion 3.V to 4.2V C1 1µF C2 1µF EN OVP 7 BRT 8 REF FB AGND PGND COMP 6 2 D1 D6 D2 D7 D3 D8 D4 D9 D5 D10 C5 0.47µF /50V 9 5 1 J4 GND R2 Open C3 0.1µF R3 C4 Open ILED 10 LED Configuration Bill of Materials Item C1, C2 C3 Part Number C1608X5R1A105K VJ0603Y104KXXAT Manufacturer TDK (1) Description Qty 1µF Ceramic Capacitor, 10V, X5R, Size 0603 (2) Vishay 2 0.1µF Ceramic Capacitor, 25V, X7R, Size 0603 1 C4 C5 Open C2012X7R1H474M DS1 L1 DFLS160-7 Diodes Inc (3) 0.47µF Ceramic Capacitor, 50V, X7R, Size 0805 1 1A, 60V, Schottky Diode 1 LQH43CN220K01L Murata(4) 22µH, 420mA ISAT., 120mΩ, (4.5mm × 3.2mm × 2.6mm) MLP3225S100L TDK(1) 10µH, 1000mA ISAT., 130mΩ, (3.2mm × 2.5mm × 1mm) LPS4012-223MLC R1 TDK(1) CRCW06031002FRT1 Coilcraft (5) (2) Vishay 22µH, 720mA ISAT., 600mΩ, (4.1mm × 4.1mm × 1.2mm) 10KΩ, 1%, 1/16W, Size 0603 R2 R3 1 1 Open CRCW060310R0FRT1 D1-D10 VLMW3100-5K8L-08 U1 MIC2297-42YML Vishay(2) 10Ω, 1%, 1/16W, Size 0603 1 Vishay 20mA Standard SMD LED PLCC-2 10 Micrel(6) 600kHz 40V PWM White LED Driver 1 (2) 1. TDK: www.tdk.com 2. Vishay-Dale: www.vishay.com 3. Diodes Inc: www.diodes.com 4. Murata: www.murata.com 5. Coilcraft: www.coilcraft.com 6. Micrel, Inc: www.micrel.com May 2008 4 M9999-053008-A Micrel, Inc. MIC2297 Evaluation Board PCB Layout Recommendations Top Layer Bottom Layer May 2008 5 M9999-053008-A Micrel, Inc. MIC2297 Evaluation Board MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2008 Micrel, Incorporated. May 2008 6 M9999-053008-A