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BD6369GUL

Parallel Interface Type Lens Drivers for Voice Coil Motor

ROHM Semiconductor 

BD6883GUL,BH6453GUL,BD6886GUL,BD6369GUL

Technical Note

7) Setting of PWM signal input VLIM and CLIM terminals (all series)

It is also possible to compose filters outside the IC, change an input voltage for output voltage and output current setting terminals

such as VLIM and CLIM terminals by the DUTY control using an PWM signal, etc., and use them as set values for control.

In this case, however, ensure the smoothing of the signals, heeding the constant number of the low-pass filter as stated below.

A cutoff frequency FC (-3dB attenuation frequency) of the low-pass filter in Fig25 is calculated by the formula mentioned below.

Cutoff frequency FC [Hz] =

1

[Hz]

2πCIN (RINA//RINB)

･････④

Set the cutoff frequency FC at 1/100 or below of the PWM frequency FPWM.

For example, if the cutoff frequency FC is set at 1/100 of FPWM when the PWM frequency FPWM=50[kHz], according to the formula

above:

Cutoff frequency FC [Hz] =

1

2πCIN (RINA//RINB)

= 1 ×FPWM= 50×103

100

100

[Hz]

･････⑤

When CIN=0.1[μF], according to the formula above:

RINA//RINB=3.2[kΩ]

･････⑥

ON time

Where, an effective value of PWM signal as a DC current, according to crest values VMAX and ON DUTY [%]= ON time+ OFF time

is as follows:

VPWM[V]= VMAX[V]× ON DUTY[%]

･････⑦

An actual voltage VLIM input to terminals that specify output current and voltages, such as VLIM and CLIM terminals

is as follows according to resistance potential division of RINA and RINB:

VLIM[V]=

RINB

RINA+RINB

×VPWM[V]

･････⑧

For example, when an PWM signal with crest values VMAX=3[V] and DUTY [%]=5[%] is input, a VLIM value according to the formula

above is:

VLIM[V]=

RINB

RINA+RINB

× 3[V]× 50[%]

･････⑨

（Ⅰ）BD6883GUL, BD6886GUL, and BD6369GUL

Where, to specify an output voltage VOH=2[V], a value VLIM=1.0[V] according to the formula in the previous page. And then,

according to the formula above, VLIM=1.0[V].

VLIM=1.0[V]=VLIM=

RINB

RINA+RINB

×3[V]×50[%]

Therefore, RINA=0.5RINB

⑩

According to ⑥ and ⑩, RINA=4.8kΩ, RINB=9.6kΩ.

･････

（Ⅱ）BH6453GUL

Where, to specify an output current ISINK=100[mA], the following formula is derived according to the formula in the previous page

③, CLIM=0.4[V], and according to the formula above ⑨:

CLIM=0.4[V]=VLIM=

RINA=2.75RINB

RINB

RINA+RINB

×3[V]×50[%]

･････⑪

According to ⑥ and ⑪: RINA=11.9kΩ, RINB=4.3kΩ

FPWM

VMAX

VPWM

RINA

VLIM Output voltage / Constant current voltage terminals

VLIM / CLIM

RINB

CIN

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© 2012 ROHM Co., Ltd. All rights reserved.

Fig.25 Example PWM signal input

11/16

2012.03 - Rev.A

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