S-8813 Datasheet, PDF (12/29 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)
S-8813 Series
Rev.2.1_00
4. ON/OFF Pin (Power Off Pin)
Setting the ON/OFF pin to the Low level ("L") causes the voltage of the CPOUT pin to change to the GND
potential and simultaneously the operation of all the internal circuit to stop. At this time, the consumption
current is largely reduced, to a level of approximately 0.3 μA.
V_IN
V_IN
ON/OFF
ON/OFF Pin
High level ("H")
Low level ("L")
Oscillator
Operating
Stopped
V_CPOUT
5.0 V
V_SS
Output Current
Setting value
0 mA
V_SS
Figure 10 Equivalent Circuit of ON/OFF Pin
5. Soft Start Function
The S-8813 Series features a built-in soft start circuit. Upon power application or when the
ON/OFF pin is switched from "L" to "H", the output voltage gradually rises over the soft start time,
and the output current is gradually output as a result. This soft start function reduces the input current
rush.
6. External Capacitor Selection
6.1 Input and Output Capacitors (C_IN, C_OUT)
The input capacitor (C_IN) lowers the power supply impedance and averages the input current, resulting in
improved efficiency.
The C_IN value is selected according to the impedance of the power supply that is used. Select a ceramic
capacitor with a small equivalent series resistance (ESR). Although this figure varies according to the
impedance of the power supply that is used as well as the load current value, it is generally in the range of
4.7 μF to 10 μF.
For the output capacitor (C_OUT), select a ceramic capacitor with a small ESR for smoothing the ripple
voltage. A value of 10 μF is recommended for the capacitance value. Use of a capacitor with a
capacitance lower than 10 μF results in a larger ripple voltage as well as a larger ripple current for the
output current.
Conversely, use of a capacitor with a capacitance greater than 10 μF results in the output voltage not
being able to rise up to 5.0 V and the impossibility to obtain the desired output current.
6.2 Pump Capacitor (C_PUMP)
The pump capacitor (C_PUMP) is required for stepping up the voltage. Select a ceramic capacitor with a
small ESR. A capacitance value of 0.22 μF is recommended. Use of a capacitor with a capacitance
greater than 0.22 μF results in a larger ripple voltage as well as a larger ripple current for the output
current. Conversely, use of a capacitor with a capacitance lower than 0.22 μF results in the output voltage
not being able to raise up to 5.0 V and the impossibility to obtain the desired output current.
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Seiko Instruments Inc.