FS98O21 datasheet(28/136 Pages) FORTUNE

28 / 136 page

FS98O21

Rev. 1.7

28/136

Power System

FS98O21 has a special power system that can supply a fixed voltage (3.6V) for CPU and ADC. FS98O21 could

work when the supply voltage is within a specified range, fixed or floating. The power system has 6 function

engines as Voltage Doubler, Voltage Regulator, Analog Bias Circuit, Common Voltage Generator Low

Battery Comparator and Band gap Voltage / Temperature Sensor

. Through the first 4 function engines, the

system can generate 3 Voltage level as VGG = 2VDDP, VDDA = 3.6V, AGND = 1.8V. Please see Figure 4-1.

Voltage Doubler

The acceptable VDD range for FS98O21 is from 2.2V to 3.6V. Voltage Doubler raises the voltage of VGG

to 2 times of VDDP

2. VGG is used as the input of Voltage Regulator. It is from 4.4V to 7.2V. Please see

Section 4.1 for detailed register setting.

Voltage Regulator

The fixed voltage is important when the Analog function is working. Voltage Regulator raises the voltage

of VDDA to fixed 3.6V. Although the input voltage of Voltage Regulator, VGG, is from 4.4V to 7.2V (It

depends on the voltage of VDD), the minimum possible voltage is still higher than 3.6V, so Voltage

Regulator could surely supply VDDA as 3.6V. Please refer to Section 4.2 for detailed register setting.

Analog Bias Circuit

Analog Bias Circuit is used to set VB to 3.6V. VB is used for FS98O21 Analog Function Network. The

user needs to enable Analog Bias Circuit, and then the Analog Functions such as ADC or OPAMP can

work correctly. Please refer to Section 4.3 for detailed register setting.

Common Voltage Generator

FS98O21 sets the analog ground to half VDDA. Please refer to Section 4.4 for detailed register setting.

Figure 4-1 FS98O21 power system block

2 VDDP means the VDD for Charge Pump (Voltage Doubler). User usually connects the VDDP to VDD.

VSSP means the VSS for Charge Pump (Voltage Doubler). User usually connects the VSSP to VSS.

VDD / VDDP

(2.2V~3.6V)

VSS / VSSP

(GND)

Voltage

Doubler

VGG = 2 VDDP

(4.4V~7.2V)

VDDA / VB

(fixed 3.6V)

Voltage

Regulator

Analog Bias

Circuit

AGND = 1/2VDDA

(fixed 1.8V)

Common

Voltage

Generator

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