ADUC7129_15 Datasheet, PDF (38/92 Pages) Analog Devices – Precision Analog Microcontroller ARM7TDMI MCU with 12-Bit ADC and DDS DAC

ADuC7128/ADuC7129
BAND GAP REFERENCE
The ADuC7128/ADuC7129 provide an on-chip band gap
reference of 2.5 V that can be used for the ADC and for the
DAC. This internal reference also appears on the VREF pin.
When using the internal reference, a capacitor of 0.47 μF must
be connected from the external VREF pin to AGND to ensure
stability and fast response during ADC conversions. This
reference can also be connected to an external pin (VREF)
and used as a reference for other circuits in the system.
An external buffer is required because of the low drive capability
of the VREF output. A programmable option also allows an external
reference input on the VREF pin. Note that it is not possible to
disable the internal reference. Therefore, the external reference
source must be capable of overdriving the internal reference source.
The band gap reference interface consists of an 8-bit REFCON
MMR, described in Table 40.
Table 40. REFCON MMR Bit Designations
Bit Description
7:1 Reserved.
0
Internal Reference Output Enable.
Set by user to connect the internal 2.5 V reference to the VREF pin. The reference can be used for external components but needs
to be buffered.
Cleared by user to disconnect the reference from the VREF pin.
Note: The on-chip DAC is functional only with the internal reference output enable bit set. It does not work with an external
reference.
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