ADS7861EB/2K5

The ADS7861 is a dual, 12-bit, 500kSPS, Analog-to-Digital (A/D) converter with four fully differential input channels grouped into two pairs for high speed, simultaneous signal acquisition. Inputs to the sample-and-hold amplifiers are fully differential and are maintained differential to the input of the A/D converter. This provides excellent common-mode rejection of 80dB at 50kHz which is important in high noise environments. The ADS7861 offers a high-speed, dual serial interface and control inputs to minimize software overhead. The output data for each channel is available as a 12-bit word. The ADS7861 is offered in both an SSOP-24 and a QFN-32 package and is fully specified over the -40°C to +125°C operating range. The ADS7861 is a high-speed, low power, dual, 12-bit A/D converter that operates from a single +5V supply. The input channels are fully differential with a typical common-mode rejection of 80dB. The part contains dual, 2μs successive approximation ADCs, two differential sample-and-hold amplifiers, an internal +2.5V reference with REFIN and REFOUT pins and a high-speed parallel interface. The ADS7861 requires an external clock. In order to achieve the maximum throughput rate of 500kSPS, the master clock must be set at 8MHz. A minimum of 16 clock cycles are required for each 12-bit conversion. There are four analog inputs that are grouped into two channels (A and B). Channel selection is controlled by the M0, M1 and A0 pins. Each channel has two inputs (A0 and A1 and B0 and B1) that can be sampled and converted simultaneously, thus preserving the relative phase information of the signals on both analog inputs. The part accepts an analog input voltage in the range of -VREF to +VREF, centered around the internal +2.5V reference. The part will also accept bipolar input ranges when a level shift circuit is used at the front end. All conversions are initiated on the ADS7861 by bringing the CONVST pin HIGH for a minimum of 15ns. CONVST HIGH places both sample-and-hold amplifiers in the hold state simultaneously and the conversion process is started on both channels. The RD pin can be connected to CONVST to simplify operation. Depending on the status of the M0, M1 and A0 pins, the ADS7861 will (a) operate in either twochannel or four-channel mode and (b) output data on both the Serial A and Serial B output or both channels can be transmitted on the A output only. The sample-and-hold amplifiers on the ADS7861 allow the ADCs to accurately convert an input sine wave of full-scale amplitude to 12-bit accuracy. The input bandwidth of the sample-and-hold is greater than the Nyquist rate (Nyquist equals one-half of the sampling rate) of the ADC even when the ADC is operated at its maximum throughput rate of 500kSPS. The typical small-signal bandwidth of the sampleand-hold amplifiers is 40MHz. Typical aperture delay time or the time it takes for the ADS7861 to switch from the sample to the hold mode following the CONVST pulse is 3.5ns. The average delta of repeated aperture delay values is typically 50ps.

Applications

• MOTOR CONTROL
• MULTI-AXIS POSITIONING SYSTEMS
• 3-PHASE POWER CONTROL

Key features

• 4 INPUT CHANNELS
• FULLY DIFFERENTIAL INPUTS
• 2µs TOTAL THROUGHPUT PER CHANNEL
• NO MISSING CODES
• 1MHz EFFECTIVE SAMPLING RATE
• LOW POWER: 40mW
• SSI SERIAL INTERFACE
• OPERATING TEMPERATURE RANGE: -40°C to ±125°C