MIC3232 Evaluation Board High Voltage Boost HBLED Driver with PWM Dimming Control Bringing the Power to Light How it works General Description The MIC3232 evaluation board is set to operate as a boost The MIC3232 is a constant current boost switching converter, which requires the output voltage to be greater controller specifically designed to power one or more than the input voltage. It is important to have the series strings of high power LEDs. The MIC3232 has an input LED forward voltage drops be greater than the input voltage range from 6V to 45V and is ideal for a variety of voltage because when the MIC3232 is off, the input is applications. The MIC3232 is the fixed 400kHz version of connected to the output through the inductor (L1) and the MIC3230, in a 10-pin MSOP package. ) is effectively applied diode (D1). The input voltage (V IN The MIC3232 utilizes an external power device which across the LEDs and will turn on if V is greater than the IN offers a cost conscious solution for driving high power LED sum of the forward voltage drops across the LED string. applications. Power consumption has been minimized For 100% duty cycle, simply pull PWMD high or leave through the implementation of a 250mV feedback voltage open. For a different LED current change R7 using the reference providing an accuracy of 3%. The MIC3232 is following equation. When R7 is 0.62 the LED current is dimmable via a PWM input signal and also features an to 0.4A. The evaluation board is currently set to this enable pin for low power shutdown. output current value. The LED current is regulated by keeping the voltage drop V REF I = Where V = 0.25 across the current sense resistor (R7) constant. The LED REF LED R7 current can be set by selecting the value of R7. In this version of the eval board, the output current is limited to PWM Dimming 1A. A PWM signal applied to the PWMD pin turns the current Table 1 provides a summary of the eval board to the LEDs on and off. When PWMD is high, the MIC3232 specifications. The evaluation board schematic is shown in is enabled and the boost converter regulates the LED Figure 1 and the parts list is shown in the Bill of Materials current by keeping the voltage drop across the R7 resistor table. constant. When PWMD is low the converter turns off and the LED current discharges the output capacitors and the Requirements LED current stops. 1. Voltage source capable of supplying 50 Watts 2. Load: LED, resistive or electronic load Ordering Information 3. Scope Part Number Description 4. Voltage meter 5. (Optional) Function generator for PWM Dimming MIC3232YMM EV Evaluation board for the MIC3232YML IC Precautions The evaluation board does not have input reverse polarity protection. Applying a negative voltage at the VIN terminal may damage the board. When the controller is off there is a current path through the inductor and the flyback diode to the output. No current limit exists for this current path so care must be taken not to short circuit the output. Micrel Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel +1 (408) 944-0800 fax + 1 (408) 474-1000 PGND Micrel, Inc. MIC3232 Evaluation Board Quick-Start Guide R Current Limit Sensing SET 1. Connect a load (LED series string or resistive load) The MIC3232 features current limit sensing. Current limit between V and LED RTN (this is not the same as is set through the external resistor, R6, by the following OUT ground). equation: 2. Connect 12V (or other input voltage) to V and I =0.5V = R6 I IN S Q1 GND. Where, I is the peak FET current that will trigger the Q1 3. Use a current probe to measure the load current. current limit, the Default setting for the evaluation board and Monitor the Switch node with a scope to view is R6 = 75m with the current limit set at 6.7A. the switch waveform OVP Setting the over voltage protection 4. PWM Dimming: OVP is set with the R9 resistor, according to equation: a. For no PWM dimming, leave the PWMD (R9 V ) terminal open O,MAX OVP = 1.245V = () b. For PWM DIMMING connect a function R8 + R9 generator to the PWM DIM input and GND On the evaluation board, these values have been set to: (not RTN). Set the output at 0-5V square = 64V. R9=2k and R8=100k and V O,MAX wave pulse at 300Hz. Make sure the pulse goes all the way to 0V. C3 R4 1000pF 100V 1/2 W L1 47H J6 J1 +Vout to LED VIN C1 D1 R1 4.7uF SS5P10-E3 MIC3232YMM 50V R8 MSOP-10 1 VIN J3 2 7 EN OVP EN Q1 J4 3 9 SI7148DP PWMD DRV C6 C7 PWMD Dim 2.2uF 2.2uF R5 6 100V 100V R10 IS OPEN 5 Vfb=0.25V R9 IADJ R6 R7 4 COMP 1/2 W 1/4W R3 10 VDD C4 C5 10nF 10uF 6.3V 8 J2 J7 GND LED RTN Figure 1. Schematic Diagram M9999-071609-A July 2009 2 (408) 944-0800