S-8813 Datasheet, PDF (17/29 Pages) Seiko Instruments Inc – 3-CHANNEL WHITE LED DRIVER IC (CHARGE PUMP IC WITH BUILT-IN CONSTANT-CURRENT CIRCUIT)

3-CHANNEL WHITE LED DRIVER IC (CHARGE PUMP IC WITH BUILT-IN CONSTANT-CURRENT CIRCUIT)
Rev.2.1_00
S-8813 Series
V_IH
V_IL
T_OFF T_ON
T
PWM Duty Ratio= ^TOFF
T
Figure 26 Wave Form Example of PWM Control signal
PWM Control Signal Conditions:
f_PWM
V_P-P
V_IH
V_IL
Min.
100 Hz
2.0 V
2.0 V
0V
Typ.
⎯
⎯
⎯
⎯
f_PWM: Pulse frequency
V_P-P: Pulse amplitude
V_IH: Pulse input voltage (“H”)
V_IL: Pulse input voltage (“L”)
Max.
20 kHz
4.5 V
4.5 V
0V
Output Impedance of the PWM Output Control Signal Source (R_Z): Max.500 Ω
Calculation of I_OUT According to PWM Duty Ratio: I_OUT=1 V / (R₁+R_Z) × 100 × (1-Duty ratio)
Ideally, when the duty ratio is 0%, I_OUT value is the 100 times value of the RISET pin voltage (1 V) divided by the
resistance of R₁. However, the impedance from the RISET pin to the GND will serve as R₁+R_Z in actual operation.
R_Z means the output impedance of the PWM control signal source when the PWM control signal is low level.
Therefore, the I_OUT value varies depend on the R_Z value.
Caution 1. Fix the PWM output to low level during standby (when the ON/OFF pin is low level). If the
PWM Output is set to high level, leak current will flow.
2. When the PWM duty is set to 100%, the current to the LED will be switched off. However, the
IC will still keep operation. This is not the same as standby mode, and so the current
consumption will be the same as in normal operation mode.
3. The duty ratio indicates the percentage of the high-level pulse width to one period.
Seiko Instruments Inc.
17