FS9701B datasheet(19/46 Pages) FORTUNE

19 / 46 page

FS970X

Rev. 4.4

19/46

Ω Power Supply

Ω power supply flows directly into decay network, providing voltage as shown in Chart

8. Among them, cap is

determined by function decoder. When cap=0, it’s not under capacity measuring mode. For DMM application, it

represents resistance measurement. At this time, the output of Ω is controlled by SOSR1:0, as shown in Chart

8. SOSR1:0 can be set up by register.

When cap = 1, it’s under capacity measuring mode. At this time, the output of Ωpower supply is irrelevant to

SOSR1:0, but controlled by TBDIV and CAPTG. When TBDIV = 0, Vrfh is approx. 1.2 V, and the

charge/discharge voltage is approx.1.2V.

When TBDIV=1, Vrfh is approx. 3.1 V (VDD), and the

charge/discharge voltage is also approx. 3.1 V. This improves the charge/discharge speed of capacity

measuring. CAPTG is the output of comparator CMP1. It controls the charge/discharge selection of Ω

power supply to the measuring capacity.

When output is VDD, theΩvoltage is the voltage on the pins, which will be affected by on/off resistors on t

path so the real voltage of the load will be affected by the load.

When output is other than VDD, the on/off resistor can be ignored because operation amplifier is high gain and

negative feedback. The real voltage of the load affected by the load can be ignored as well. Under all kinds of

output, the maximum power is approx. 1.2mA.

INPUT

OUTPUT

cap

TBDIV

CAPTG

SOSR1:0

OSRO

high impendence

AX5

Vrfh

VDD

Vrfh (REFH)

AGND

Vrfh (VDD)

AGND

Chart 8

Ω power supply true-value Chart

FS9701B датащи(PDF) 19 Page - Fortune Semiconductor Corp.