FS970X datasheet(18/46 Pages) FORTUNE

18 / 46 page

FS970X

Rev. 4.4

18/46

10..1

Area Network Switch

Combining area network switch to an external high-precision resistor becomes a measurement network. It

transfers the signal of the sensor into suitable voltage range for ADC and measures the signal. The function

decoder controls the measurement range and on/off status. See Graph 5 and Section 7.1 for details.

Take DC5V as an example, using Chart 6 as reference, setting MODE3:0=0000 and RANGE=0001 will make

onek2:0=tenk2:0=hunk2:0=000, onem2:0=011, and tenm1:0=01. When corresponding this value to the area

network of the low-left corner of Graph 5, all the switches are under open status except for tenm<0>, onem<1>,

and onem<2>. Thus, connecting to an external resistor network will make up a ten-times decay circuit to

achieve the decay function required by DC5V.

Fixed Voltage Generator

When under capacity measuring, short testing, and resistor measuring, all the required power supply is

provided by this block.

The output of this block includes Vcntd, Vsrc1, Vcapd1, Vcapd2, Vcapc2, Vcapc1, and Vrfh. The output voltage

is controlled by vsr and TBDIV, as shown below. Vsr comes from the decoding of MODE3:0 input by function

decoder. TBDIV can be directly set up by register.

INPUT

OUTPUT

vsr

TBDIV

Vrfh

Vcapc1 Vcapc2 Vcapd2 Vcapd1

Vsrc1

Vcntd

1.2 V

0.8 V

0.64 V

0.56 V

0.4 V

0.16 V

0.04 V

3.1 V

1.58 V

1.65 V

1.45 V

1.52 V

0.4 V

0.1 V

0 V

Chart 7. Voltage output of fixed voltage generator.

When TBDIV=0, the block refers to the voltage of REFH, as shown in Chart 7, REFH=1.2V. And if REFH =

0.6V, the voltage generated are 0.6V, 0.4 V, 0.32 V, 0.28 V, 0.2 V, 0.08 V, and 0.02 V. When TBDIV=1, it refers

to the voltage of VDD, as shown in Chart 7, which is the voltage output of VDD voltage being 3.1 V under

normal condition.

Vrfh is the reference voltage of ohm power supply when measuring resistance and capacity. Vcapc1 and

Vcapd1 are respectively the reference voltage of charge/discharge comparator Vcapc1 (charging) and Vacpd1

(discharging) when measuring capacity. Vcapc2 and Vcapd2 are the second set of reference voltage of

charge/discharge comparator. According to the measuring capacity range, one set of the reference voltage can

be selected by CAPM setup of register. (See Chart 14 for details). Vcntd is the reference voltage of comparator

under short testing. There is no special function of Vsrc1, users can customize it according to their needs.

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