Light emission driving device and driving method thereof

A light emission driving device comprising:

• a light emitting unit;
• a driving current generating unit configured to supply a driving current according to a driving signal to the light emitting unit;
• a light detecting unit configured to detect emitted light from the light emitting unit;
• a first automatic light output control circuit and a second automatic light output control circuit configured to adjust the driving signal to the driving current generating unit in accordance with a detection light intensity of the light detecting unit and to control an intensity of the emitted light to a predetermined target light intensity;
• a circuit switching unit configured to switch between the first automatic light output control circuit and the second automatic light output control circuit in response to a switching signal;
• and
• a control unit configured to instruct the first automatic light output control circuit and the second automatic light output control circuit to reach the target light intensity, wherein
• the first automatic light output control circuit has a first time constant to reach the target light intensity,
• the second automatic light output control circuit has a second time constant larger than the first time constant to reach the target light intensity, and
• the control unit:
• switches to the first automatic light output control circuit by the circuit switching unit at startup;
• and
• when a predetermined time has passed after the intensity of the emitted light has reached the target light intensity, switches to the second automatic light output control circuit by the circuit switching unit and supplies an initial signal causing the second automatic light output control circuit to output the driving signal corresponding to the target light intensity.