Texas Instruments MSC1210 manual Voltage Reference, 5.Output Data Rate and Channel Rate 10x faster

Voltage Reference

Notice that the speed difference for the synchronized channel changes are only different by a factor of 3, whereas the non-synchronized channel has a factor difference of 4.5.

These rates are all based on a reasonable speed for the modulation clock. In many applications, the mod clock can run as much as 10 times faster. That would make all of the times for throughput also 10 times faster, as shown in Table 12−5.

Table 12−5.Output Data Rate and Channel Rate (10x faster)

	Data Rate	Channel Rate	Synchronized
Filter	(Hz)	(Hz)	(Hz)
Sinc3 (dec = 200)	780.125	/4 = 190.53	/3 = 260.04
Sinc2 (dec = 500)	310.25	/3 = 100.41	/2 = 150.625
Fast Settling (dec = 1800)	80.68	/2 = 40.34	/1 = 80.68

12.12 Voltage Reference

The voltage reference used for the MSC1210 can either be internal or external. The power-up configuration for the voltage reference is 2.5V internal. The selection for the voltage reference is made through the ADCON0 register, bits 5 (internal/external selection) and 4 (1.25V/2.5V internal reference voltage).

Internal voltage reference is enabled by setting ADCON0.5 (EVREF, SFR ad- dress:0xDC), which is the default condition. When internal voltage reference is enabled, it may be selected as either 1.25V or 2.5V depending on the setting of ADCON0.4 (VREFH). Setting this bit sets the internal reference voltage to 2.5V, while clearing it sets the internal reference voltage to 1.25V (AVDD = 5V only).

When external voltage is selected, the external voltage reference is differential and is represented by the voltage difference between pins +VREF and −VREF. The absolute voltage on either pin (+VREF and −VREF) can range from AGND to AVDD, however, the differential voltage must not exceed 5V. The differential voltage reference provides an easy means of performing ratiometric measure- ment.

The REFOUT pin should have a 0.1∝F capacitor to AGND.

Note:

Enabling the internal VREF does not eliminate the need for an external con- nection. The REFOUT pin must still be connected to VREF+, and VREF− must still be connected to AGND for normal operation with internal VREF. The only thing that enabling internal VREF does is enable the REFOUT pin.

Analog-to-Digital Converter 12-15