5 AFE with Internal Voltage Reference Source

5.1 Hardware Setup of AFE with Internal Voltage Reference

The SLG47004 allows powering all analog components of the AFE (sensor, DAC, and reference for Chopper ACMP) from an internal voltage source, see Figure 12. For this purpose, the SLG47004 has a special high drive buffer (HD Buffer macrocell).

Figure 12: Analog Front-End with Internal Voltage Reference

5.2 Precision Characteristics of Sensor at 2.048 V Supply Voltage

Characteristics of the pressure sensor at 2.048 V supply voltage are shown in Table 4. All other precision characteristics from Table 1 remain unchanged.

Table 4: Characteristics of Sensor at 2.048 V Supply Voltage

Parameter	Description	Value	Unit
ΔP	Pressure Range	±6.0	kPa
KVout	Output Voltage Span	±5.04 (min), ±5.32 (typ), ±5.73 (max)	mV
Kos_out	Null Offset	±0.154 (max)	mV
dVos_bridge/dT	Offset Temperature Drift (T = 0 to 50 °C)	±0.6 (max)	%FSS

5.3 Internal Macrocells Configurations

5.3.1 HD Buffer and OpAmp0 Vref Configurations

The HD Buffer shares the voltage reference with OpAmp0 Macrocell. Note that Vref can be connected (or disconnected) to OpAmp0 or HD Buffer macrocells independently. The configurations of HD Buffer and OpAmp0 Vref are shown in Figure 13.

Figure 13: OpAmp Vref and HD Buffer Configurations

5.3.2 Chopper ACMP Configuration for AFE with 2.048 V Voltage Reference

Chopper ACMP configuration is shown in Figure 14.

Figure 14: Chopper ACMP Configuration for AFE with 2.048 V Voltage Reference

5.4 Gain Resistor and DAC Divider Calculations for AFE with 2.048 V Voltage Reference

Considering the output span of the sensor (from 5.04 mV to 5.73 mV at V_an= 2.048 V), the output voltage range of AFE must be:

Using equation (3),

Gain resistor R_g= 1.33 kΩ, R_f= 100 kΩ. The range of offset compensation is V_comp= ±(177.9*0.00215) = 0.382 V. The divider resistorsR_div1= 21.3 kΩ,R_div2= 46.4 kΩ. The offset of the HD Buffer is 3 mV.