C8051F012 查看數據表（PDF） - Silicon Laboratories

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C8051F012

Mixed-Signal 32KB ISP FLASH MCU Family

Silicon Laboratories 

C8051F000/1/2/5/6/7

C8051F010/1/2/5/6/7

9. VOLTAGE REFERENCE

The voltage reference circuit consists of a 1.2V, 15ppm/°C (typical) bandgap voltage reference generator and a

gain-of-two output buffer amplifier. The reference voltage on VREF can be connected to external devices in the

system, as long as the maximum load seen by the VREF pin is less than 200µA to AGND (see Figure 9.1).

If a different reference voltage is required, an external reference can be connected to the VREF pin and the internal

bandgap and buffer amplifier disabled in software. The external reference voltage must still be less than AV+ -

0.3V. The Reference Control Register, REF0CN (defined in Figure 9.2), provides the means to enable or disable

the bandgap and buffer amplifier. The BIASE bit in REF0CN enables the bias circuitry for the ADC and DACs

while the REFBE bit enables the bandgap reference and buffer amplifier which drive the VREF pin. When

disabled, the supply current drawn by the bandgap and buffer amplifier falls to less than 1uA (typical) and the

output of the buffer amplifier enters a high impedance state. If the internal bandgap is used as the reference voltage

generator, BIASE and REFBE must both be set to 1. If an external reference is used, REFBE must be set to 0 and

BIASE must be set to 1. If neither the ADC nor the DAC are being used, both of these bits can be set to 0 to

conserve power. The electrical specifications for the Voltage Reference are given in Table 9.1.

The temperature sensor connects to the highest order input of the A/D converter’s input multiplexer (see Figure 5.1

and Figure 5.5 for details). The TEMPE bit within REF0CN enables and disables the temperature sensor. While

disabled, the temperature sensor defaults to a high impedance state and any A/D measurements performed on the

sensor while disabled result in meaningless data.

Figure 9.1. Voltage Reference Functional Block Diagram

AV+

R1

External

Voltage

Reference

Circuit

AGND

External Equivalent

Load Circuit

VREF

RLOAD

TEMPE

BIASE

REFBE

EN Temp

Sensor

EN Bias

Generator

AGND

EN 2.4V

Reference

AGND

(to Analog Mux)

(Bias to ADC

and DAC)

(to ADC

and DAC)

AGND

Rev. 1.7

60

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