
LB8658FN, LB8658PL 
No.7983-14/16
(6) Constant-current rising offset function 
The rising waveform of the coil current can be offset by having the external CR network give a slope to the rising 
waveform of the voltage input to the IC pin and setting a greater coil time constant to make the slope more gradual. 
This ensures stable shutter operation under severe power voltage fluctuations. 
Note : When offsetting the rising waveform of the coil current using the IC pin, assume the VB1 voltage that could 
be obtained in the absence of the capacitor to the IC pin as the supposed minimum voltage and observe and 
confirm the rising waveform of the coil current that flows at that voltage, then determine the capacitance of 
the capacitor so as to yield a time constant value that is greater than the one that could produce the 
waveform generated at the supposed minimum voltage. 
The rising waveform offsetting capacitor is unnecessary if the power voltage supplied is stable or in similar cases 
in which the rising waveform offsetting function is not required. 
(7) FC pin phase compensation capacitor  
The capacitor connected to the FC pin is used for phase compensation of constant-current control between  
OUT9 and OUT10.  
Test capacitor values between 0.0015
μ
F to 0.033
μ
F and choose a value that does not cause output oscillation 
problems. (In particular, when a large-inductance coil is used, it is necessary to provide a margin to a  
capacity value.) 
Moreover, since the constant-current control block is connected to PGND inside the IC, GND side of the FC pin  
capacitor must be connected to PGND.  
(Cautions for FC pin capacitor setting) 
For the capacitor value setting, set the value by which the output does not oscillate, observing an output voltage  
waveform.  
In circuit, the FC pin is connected to the output part of the constant-current control amplifier, and an output  
transistor drives because the potential of the FC pin rises. That is, since the initial state of the FC pin influences the  
output-drive timing, the potential of the FC pin is discharged (fast discharge circuit) inside the IC to a certain level  
before the shutter is ON, and the potential of the FC pin is charged (fast charge circuit) inside the IC to a certain  
level when a shutter is ON, so that the state of the FC pin during shutter driving can always be constant on this IC.  
This allows constant input/output delay time.  
However, since the time involved in charge/discharge in the above-mentioned circuit will be long if the capacitor  
value setting is too large, the amount of variation in charge/discharge delay time will increase with the variation of  
capacitor value (absolute value variation and temperature characteristic).  
Moreover, as another negative effect of setting a large value to the capacitor, it is considered that the rising  
inclination of coil current is moderate. Although the rising inclination of coil current originally depends on  
L component of the coil, if a large value is set to a capacitor and the capacitor time constant increases, the rising  
inclination of coil current depends on the value of the capacitor.  
For the reasons mentioned above, especially in the applications in which a high-speed shutter drive is required,  
both the value by which output does not oscillate and as small a value as possible (0.0015
μ
F to 0.033
μ
F) 
must be set to a capacitor which is connected to the FC pin.  
ILB01686 
IC pin voltage
Coil current
VB1 is high. (Without IC capacitor)
Rising offset 
IC discharging 
Shutter “Close” operating 
Rising offset coil current
VB1 is low. (Without IC capacitor)