ALLEGRO APM80951KNBATR

The customer's APM80951 evaluation board is configured for internal PWM dimming operation mode, so no external PWM dimming signal needs to be applied at test point PWM when using the evaluation board as-is. The internal PWM dimming frequency is set to 200Hz, and the dimming duty cycle is set to approximately 69%. To disable internal PWM dimming, replace Rdrt with a 0Ω resistor to connect the DR pin to VCC (refer to the schematic above). Place a jumper on connector P1 to connect EN to VIN through a resistor to enable the device. The RngH or RngL resistor determines whether the LED current range is high or low:

1. The LED current level is determined by the current sense resistor on the board: LED current i_LED = 0.2 / R_sense (A) On the evaluation board, there is one current sense resistor, Rs1 = 0.2Ω. Since RNG = VCC, the full LED current is 1A.
2. The internal PWM dimming frequency is given by: f_PWM = 14000 / R_FPWM where R_FPWM is in kΩ and f_PWM is in Hz; on the evaluation board, R_FPWM = 69.8kΩ sets an internal dimming frequency of 200Hz. The internal PWM dimming duty cycle can be estimated by: D_PWM = (V_DR / 0.036) × 100%
3. Apply an external analog dimming signal at test point ADIM. Do not leave the ADIM pin floating. The ADIM pin voltage controls the LED current reference voltage across Rs1 according to: V_CSREG = (V_ADIM - 0.4) / 5 (V) Calculations and actual test results are provided below as a reference for selecting the desired ADIM voltage. ADIM vs. LED Current Reference Voltage: RNG = High VCS vs. ADIM at RNG = High ADIM vs. LED Current Reference Voltage: RNG = Low VCS vs. ADIM at RNG = LOW

To enable the evaluation board, short connector P1 using the included jumper to connect EN to VIN, or apply a voltage greater than 1.8V at test point EN if no jumper is used. Apply the desired ADIM voltage at the ADIM test point. For internal PWM dimming mode, no PWM signal needs to be applied at the PWM test point; however, for external PWM dimming mode, a PWM signal must be applied at the PWM test point. Connect the LED load between LED+ and GND; apply input power.

Efficiency vs. 2 WLED Load 10% External PWM Dimming Waveform at V_VIN = 12V Input Startup Waveform at 2 WLEDs, V_VIN = 12V 12 to 20V VIN Transient at 2 WLEDs, V_VIN = 12V PWM Turn-On Waveform at 2 WLEDs PWM Turn-Off Waveform at 2 WLEDs

Thermal Shutdown at 173.8°C Thermal Recovery at 140°C Thermal Image at V_VIN = 12V, 2 WLEDs / 1A, Efficiency η = 89% Thermal Image at V_VIN = 24V, 2 WLEDs / 1A, Efficiency η = 82%

V_VIN = 12V, Load = 2 series white LEDs, I_LED = 0.5A, with EMI filter as shown, ambient temperature T_A = 25°C EN55025/CISPR25 Class 5 Peak and Average Conducted Emissions (150kHz to 108MHz) EN55025/CISPR25 Class 5 Peak and Average Biconical Radiated Emissions (Horizontal, 30 to 330MHz) EN55025/CISPR25 Class 5 Peak and Average Rod Antenna Radiated Emissions (150kHz to 30MHz) EN55025/CISPR25 Class 5 Peak and Average Biconical Radiated Emissions (Vertical, 30 to 330MHz)