LTC2410 24-Bit No Latency ∆ΣTM ADC with Differential Input and ...

LTC2410APPLICATIO S I FORATIOU W U Usynchronized with an outside source, the LTC2410 canoperate with an external conversion clock. The converterautomatically detects the presence of an external clocksignal at the F O pin and turns off the internal oscillator. Thefrequency f EOSC of the external signal must be at least2560Hz (1Hz notch frequency) to be detected. The externalclock signal duty cycle is not significant as long as theminimum and maximum specifications for the high andlow periods t HEO and t LEO are observed.While operating with an external conversion clock of afrequency f EOSC , the LTC2410 provides better than 110dBnormal mode rejection in a frequency range f EOSC /2560±4% and its harmonics. The normal mode rejection as afunction of the input frequency deviation from f EOSC /2560is shown in Figure 4.Whenever an external clock is not present at the F O pin, theconverter automatically activates its internal oscillator andenters the Internal Conversion Clock mode. The LTC2410operation will not be disturbed if the change of conversionclock source occurs during the sleep state or during thedata output state while the converter uses an externalserial clock. If the change occurs during the conversionstate, the result of the conversion in progress may beoutside specifications but the following conversions willnot be affected. If the change occurs during the data outputstate and the converter is in the Internal SCK mode, theserial clock duty cycle may be affected but the serial datastream will remain valid.NORMAL MODE REJECTION (dB)–80–85–90–95–100–105–110–115–120–125–130–135–140–12 –8 –4 0 4 8 12DIFFERENTIAL INPUT SIGNAL FREQUENCYDEVIATION FROM NOTCH FREQUENCY f EOSC /2560(%)2410 F04Figure 4. LTC2410 Normal Mode Rejection WhenUsing an External Oscillator of Frequency f EOSCTable 3 summarizes the duration of each state and theachievable output data rate as a function of F O .SERIAL INTERFACE PINSThe LTC2410 transmits the conversion results and receivesthe start of conversion command through a synchronous3-wire interface. During the conversion andsleep states, this interface can be used to assess theconverter status and during the data output state it is usedto read the conversion result.Table 3. LTC2410 State DurationState Operating Mode DurationCONVERT Internal Oscillator F O = LOW 133ms, Output Data Rate ≤ 7.5 Readings/s(60Hz Rejection)F O = HIGH160ms, Output Data Rate ≤ 6.2 Readings/s(50Hz Rejection)External Oscillator F O = External Oscillator 20510/f EOSC s, Output Data Rate ≤ f EOSC /20510 Readings/swith Frequency f EOSC kHz(f EOSC /2560 Rejection)SLEEPAs Long As CS = HIGH Until CS = LOW and SCKDATA OUTPUT Internal Serial Clock F O = LOW/HIGH As Long As CS = LOW But Not Longer Than 1.67ms(Internal Oscillator)(32 SCK cycles)F O = External Oscillator with As Long As CS = LOW But Not Longer Than 256/f EOSC msFrequency f EOSC kHz(32 SCK cycles)External Serial Clock withAs Long As CS = LOW But Not Longer Than 32/f SCK msFrequency f SCK kHz(32 SCK cycles)15