MIC2297 Evaluation Board 600kHz 42V OVP PWM White LED Driver The MIC2297 evaluation board is tailored for a single or General Description dual Li-Ion input source. The input voltage should never The MIC2297 is a 600kHz PWM White LED Driver exceed 10V. optimized for 6 to 10 series WLEDs. With an output voltage of up to 42V and a guaranteed 1.2A on the internal Getting Started power switch, the MIC2297 can easily drive 10 WLEDs at 1. Connect an external supply to V . Apply desired IN 20mA continuous current. The MIC2297 features WLED input voltage to the V (J1) and ground (J4) IN brightness control using the BRT pin and has output over terminals of the evaluation board, paying careful voltage protection (OVP) to protect the device in case the attention to polarity and supply voltage (2.5V V IN WLEDs are disconnected unexpectedly. Available in a tiny 10V). An ammeter may be placed between the 10-pin 2.5mm x 2.5mm x 0.85mm MLF package, the input supply and the V (J1) terminal to the IN MIC2297 solution only requires a total of 6 external evaluation board to accurately monitor the input components. current. The ammeter and/or power lead resistance can reduce the voltage supplied to the The MIC2297 operates at a default (BRT pin is open) input therefore, the supply voltage at the V (J1) feedback voltage of only 200mV. The low feedback IN terminal should be monitored. voltage reduces the power dissipation from the external current set resistor and increases total operating 2. Enable/Disable the MIC2297. To enable the efficiency. MIC2297, apply a 1.5V or greater voltage signal to When brightness control is required, the MIC2297 features the EN (J2) terminal. To disable the device, pull brightness control by applying a DC voltage to the BRT the EN (J2) pin below 0.4V. The evaluation board pin. When applying a DC voltage to the BRT pin, the is configured with a jumper (JP1) from V to the IN feedback voltage is equal to the BRT voltage divided by 5. enable pin and a 10k pull-down resistor to ground This feature essentially increases or decreases the to conveniently turn the part on or off. Connecting feedback voltage from its default value (200mV), changing the jumper (JP1) will enable the MIC2297, while the WLED current to control the WLED brightness. removing the jumper will disable the part. Alternatively, a PWM signal may also be applied to the 3. DCV Brightness Control. To control the BRT pin for brightness control. When a PWM signal (1kHz brightness with a DC voltage, see the DVC recommended) is applied to the BRT pin, the WLEDs are Brightness Control section. dimmed depending on the duty cycle and the peak voltage of the signal. The PWM frequency can range from 1kHz to 4. PWM Brightness Control. To control the 1MHz. The selected PWM frequency does not affect the brightness with a PWM Signal, see the PWM WLED brightness. Assuming a 1V PWM signal is applied, Brightness Control section. as the duty cycle decreases, the feedback voltage decreases, thus reducing the WLED current. Note: For detailed specifications, please refer to the MIC2297 Datasheet at www.micrel.com. Requirements The MIC2297 evaluation board requires an input power source that is capable of delivering greater than 1.2A at Ordering Information 2.5V. Part Number Description Precautions Evaluation board with the MIC2297-42YML EV The evaluation board does not have reverse polarity MIC2297 42V device protection. Applying a negative voltage to the V terminal IN may damage the 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 Micrel, Inc. MIC2297 Evaluation Board 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 ) is equal LED to the feedback voltage (V = 200mV by default) divided FB by the R3 resistance value. The evaluation board is provided with R3 equal to 10 . The brightness level is proportional to I . Programming the feedback voltage LED changes the I , therefore changing the brightness level. LED I = V / R3 (1) LED FB 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 TIME (400s/div) BRT pin, the feedback voltage is changed from the default value of 200mV to: Figure 2. BRT = 2V, V = 400mV, I = 40mA FB LED V = BRT / 5 (2) FB PWM Brightness Control Assuming BRT equals 1V, then V will be 200mV and FB The brightness level can also be set by applying a PWM ILED may be calculated by: signal to the BRT pin. To calculate the feedback voltage I = V / R3 LED FB when a PWM signal is applied to the BRT pin, use the I = 200mV / 10 following formula: LED V = V / 5 * D (3) I = 20mA LED FB PEAK Similarly, if BRT equals 2V, then V will be 400mV and V is the peak of the PWM voltage and D is the duty PEAK FB cycle. If V is 1V and the duty cycle is 1%, then V can the I may be calculated by: LED PEAK FB be calculated by: I = V / R3 LED FB V = 1V / 5 * 0.01 FB I = 400mV / 10 LED V = 2mV FB I = 40mA LED The I can then be calculated by: LED The feedback voltage can be changed using the BRT pin. Changing the feedback voltage changes the WLED I = V / R3 LED FB current, which will change the WLED brightness. Refer to I = 2mV / 10 LED the Figure 1 and Figure 2 for reference. I = 200A LED Similarly, if the V is 1V and the duty cycle is 50%, then PEAK V can be calculated by: FB V = 1V / 5 * 0.5 FB V = 100mV FB The I can then be calculated by: LED I = V / R3 LED FB I = 100mV / 10 LED I = 10mA LED 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 (400s/div) Figure 1. BRT = 1V, V = 200mV, I = 20mA FB LED May 2008 2 M9999-053008-A BRT Voltage Feedback Voltage (DC Coupled) (DC Coupled) (1V/div) (50mV/div) BRT Voltage Feedback Voltage (DC Coupled) (DC Coupled) (1V/div) (100mV/div)