FS970X datasheet(22/46 Pages) FORTUNE

22 / 46 page

FS970X

Rev. 4.4

22/46

Operation Amplifier and Comparator

The block composed by operation amplifier and comparator include AC buffer block, full-wave rectifiers block,

and comparator block.

ACDIV

ACBUF

ACEN

90 k 

10 k 

ACDIV

BPACBF

CMPH

ACBO

AGND

Graph 6. AC buffer block.

As shown in Graph 6, buffer block is controlled by ACBUF and ACDIV. It becomes a gain network when

connecting with an external resistor. Whether ACBUF works or not can be directly controlled by ACEN. When

ACEN=0, it turns off the buffer and the output becomes high impedance.

Signal enters through CMPH, and flows out from ACBO or the 37th pin ACB. ACDIV can at the same time

controls the gain. If ACDIV=0, the gain of the buffer is 1. If ACDIV=1, the gain of the buffer is determined by

the external network resistor. In Typical Application Circuit, the gain becomes 10.

When the gain is 1, the 100 kHz side wave flowing through the buffer will be reduced to lower than 0.5%. The

bandwidth of AC is limited by the frequency response of full-wave rectifier.

If the signal bandwidth is higher than100 kHz, let BPACBF=1, it will change the output source to the 38th pin

(ACA) instead of AC buffer.

EXTD

15 k 

RCTOP

RCTEN

15 k 

12.3k 

RCTP

RCTN

RCTO

ACLO

ACHO

Graph 7. Full-wave rectifier switch block

FS970X Datasheet(PDF) 22 Page - Fortune Semiconductor Corp.