Datasheet

ADuC7128/ADuC7129
Rev. 0 | Page 38 of 92
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 V
REF
pin.
When using the internal reference, a capacitor of 0.47 µF must
be connected from the external V
REF
pin to AGND to ensure
stability and fast response during ADC conversions. This
reference can also be connected to an external pin (V
REF
)
and used as a reference for other circuits in the system.
An external buffer is required because of the low drive capability
of the V
REF
output. A programmable option also allows an external
reference input on the V
REF
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 V
REF
pin. The reference can be used for external components but needs
to be buffered.
Cleared by user to disconnect the reference from the V
REF
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.