30V 1.5A 1MHz Sync Step-Down Dimmable LED Driver

Functional Block Diagram

Bias&Ref

Dimming Curve

Conversion

Regulator

Error Amplifier

Slope

Compensation

Comparator

Fault

Detection

1MHz

Clock

OTP

Driver

Valley Curve

Detection

Peak Curve

Detection

DIM

FB

IN

BS

SW

GND

Block Diagram

Functions Description

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) protects the chip from operating at an insufficient supply voltage. UVLO protection

monitors the internal regulator voltage. When the voltage is lower than UVLO threshold voltage, 4.1V(typical), the

device is shut off. The UVLO threshold has approximately 400mV of hysteresis, so the part operates until VIN

drops below 3.7V(typical). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic.

Dimming and Enable/Disable

When the input voltage is above maximal UVLO rising threshold and the DIM pin is pulled high (above 1.2V), the

HM2802 is enabled. When the DIM pin is pulled low (below 0.55V), the HM2802 goes into shutdown mode. In

shutdown mode, less than 1μA input current is consumed. The DIM pin allows disabling and enabling of the device

as well as brightness control of the LEDs by applying a PWM signal. When a PWM signal is applied, the LED

current is turned on when the DIM is high and off when DIM is pulled low. Changing the PWM duty cycle therefore

changes the LED brightness. Meanwhile, add a 0.65V to 1.2V voltage to the DIM to adjust the LED current linearly.

When dimming is not needed, we can connect DIM and VIN through a resistor.