LED driver chip for car reading light and state control method thereof
An LED driver chip for a car reading light and a state control method thereof are provided. The LED driver chip includes a state machine control circuit module, a state machine output logic module, a current on/off control logic circuit module, and a current source module. An OUT pin of the LED driver chip is connected with an LED. The LED driver chip determines the next state of LED current according to a driver chip PWM input signal, an EN pin low lever pulse input signal, and a present LED state, enabling the LED to switch among nine different states.
1. A state control method of an LED (light emitting diode) driver chip for a car reading light comprising, an OUT pin of the LED driver chip is connected to an LED; the LED driver chip, according to three signals, namely, a driver chip PWM input signal, an EN pin low lever pulse input signal, and a current LED state, and according to conversion conditions and a control signal output formula
SS=EN_EFF,PWM_ACT,LAST_STATE_PWM,PWM_PIN,GA<1>,GA<62>
determining a next state of LED current; wherein the states of the LED driver chip includes:
(1) (S0) Initial OFF: an initial off state, namely, an initial state of the driver chip, a Fade mode, an EN input signal controlling the LED current;
(2) (S1) Fade In: a state that DC current of the LED is gradually increased, the EN input signal controlling the DC current of the LED to gradually increase;
(3) (S2) LED ON Due to Fade In: a state that the DC current of the LED reaches a maximum output value, the EN input enables the LED current;
(4) (S3) Fade Out: a state that the DC current of the LED is gradually decreased, the EN input signal controlling the DC current of the LED to gradually decrease;
(5) (S4) LED On Due to PWM is ON: a state that the DC current of the LED is the maximum output value, the PWM input enables the LED current;
(6) (S5) LED PWM Ramp Down: a state that a PWM input signal controls the LED current and the duty cycle of the LED current is gradually decreased;
(7) (S6) LED Fade In From LED=0: a state that the DC current of the LED is gradually increased from 0 ampere, the EN input signal controlling the DC current of the LED to gradually increase;
(8) (S7) LED PWM Ramp Up: a state that the PWM input signal controls the LED current and the duty cycle of the LED current is gradually increased;
(9) (S8) LED PWM Mixed Fade Out: a state that the LED current is simultaneously controlled by the EN input signal and the PWM input signal.