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MAX1243AMJA Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX1243AMJA Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 12 page +2.7V to +5.25V, Low-Power, 10-Bit Serial ADCs in SO-8 _______________________________________________________________________________________ 7 AIN TRACK INPUT HOLD GND TRACK HOLD 9k RIN CHOLD 16pF - + CSWITCH COMPARATOR ZERO REF CAPACITIVE DAC AT THE SAMPLING INSTANT, THE INPUT SWITCHES FROM AIN TO GND. SHUTDOWN INPUT ANALOG INPUT 0V TO VREF +2.7V to +5.25V 1 2 3 4 VDD AIN SHDN REF 8 7 6 5 SCLK CS DOUT GND SERIAL INTERFACE C* *4.7 µF, MAX1242 0.1 µF, MAX1243 4.7 µF 0.1µF REFERENCE INPUT MAX1243 MAX1242 MAX1243 Figure 3. Operational Diagram Figure 4. Equivalent Input Circuit where RIN = 9kΩ, RS = the input signal’s source imped- ance, and tACQ is never less than 1.5µs. Source imped- ances below 4k Ω do not significantly affect the ADC’s AC performance. Higher source impedances can be used if a 0.01µF capacitor is connected to the analog input. Note that the input capacitor forms an RC filter with the input source impedance, limiting the ADC’s input signal bandwidth. Input Bandwidth The ADC’s input tracking circuitry has a 2.25MHz small-signal bandwidth, so it is possible to digitize high-speed transient events and measure periodic sig- nals with bandwidths exceeding the ADC’s sampling rate by using undersampling techniques. To avoid aliasing of unwanted high-frequency signals into the frequency band of interest, anti-alias filtering is recom- mended. Analog Input Protection Internal protection diodes, which clamp the analog input to VDD and GND, allow the input to swing from GND - 0.3V to VDD + 0.3V without damage. However, for accurate conversions near full scale, the input must not exceed VDD by more than 50mV, or be lower than GND by 50mV. If the analog input exceeds 50mV beyond the supplies, limit the input current to 2mA. Internal Reference (MAX1242) The MAX1242 has an on-chip voltage reference trimmed to 2.5V. The internal reference output is con- nected to REF and also drives the internal capacitive DAC. The output can be used as a reference voltage source for other components and can source up to 400µA. Bypass REF with a 4.7µF capacitor. Larger capacitors increase wake-up time when exiting shut- down (see Using SHDN to Reduce Supply Current). The internal reference is enabled by pulling the SHDN pin high. Letting SHDN float disables the internal refer- ence, which allows the use of an external reference, as described in the External Reference section. External Reference The MAX1242/MAX1243 operate with an external refer- ence at the REF pin. To use the MAX1242 with an external reference, disable the internal reference by let- ting SHDN float. Stay within the voltage range 1.0V to VDD to achieve specified accuracy. The minimum input impedance is 18k Ω for DC currents. During conver- sion, the external reference must be able to deliver up to 250µA of DC load current and have an output impedance of 10 Ω or less. The recommended mini- mum value for the bypass capacitor is 0.1µF. If the ref- erence has higher output impedance or is noisy, bypass it close to the REF pin with a 4.7µF capacitor. |
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