AD7843 Analog Devices, AD7843 Datasheet
AD7843
Specifications of AD7843
Available stocks
Related parts for AD7843
AD7843 Summary of contents
Page 1
... The part operates from a single 2 5.25 V power supply and features throughput rates greater than 125 kSPS. The external reference applied to the AD7843 can be varied from while the analog input range is from ...
Page 2
... AD7843 TABLE OF CONTENTS Specifications..................................................................................... 3 Timing Specifications .................................................................. 4 Absolute Maximum Ratings............................................................ 5 ESD Caution.................................................................................. 5 Pin Configuration and Function Descriptions............................. 6 Terminology ...................................................................................... 7 Typical Performance Characteristics ............................................. 8 Circuit Information ........................................................................ 11 ADC Transfer Function............................................................. 11 Typical Connection Diagram ................................................... 11 REVISION HISTORY 3/04—Data Sheet Changed from Rev Rev. B Updated Format..................................................................Universal Changes to Absolute Maximum Ratings ....................................... 5 Addition to the PD0 and PD1 Section ...
Page 3
... V max 0.4 V max ±10 µA max 10 pF max Straight (Natural) Binary 12 DCLK Cycles max 3 DCLK Cycles min 125 kSPS max Rev Page AD7843 Test Conditions/Comments GND µA typ f = 12.5 kHz SAMPLE 0.001 µA typ CC Typically 10 nA ...
Page 4
... V when loaded with the circuit in Figure 2. The measured number is then extrapolated 12 back to remove the effects of charging or discharging the 50 pF capacitor. This means that the time, t time of the part and is independent of the bus loading. 1 AD7843A Unit 2.7/3.6 V min/max 380 µ ...
Page 5
... Rev Page AD7843 ...
Page 6
... BUSY BUSY Output. Logic Output. This output is high impedance when CS is high. 14 DIN Data In. Logic input. Data to be written to the AD7843 control register is provided on this input and is clocked into the register on the rising edge of DCLK (see the Control Register section Chip Select Input ...
Page 7
... The input signal is fully acquired to the 12-bit level within this time even with the maximum specified DCLK frequency. See the Analog Input section for more details. On Resistance This is a measure of the ohmic resistance between the drain and source of the switch drivers. Rev Page AD7843 ...
Page 8
... AD7843 TYPICAL PERFORMANCE CHARACTERISTICS 207 206 205 204 203 202 201 200 199 198 –40 – TEMPERATURE (°C) Figure 4. Supply Current vs. Temperature 230 f 220 SAMPLE REF 210 200 190 180 170 160 150 2.2 2.6 3.0 3.4 3.8 +V (V) CC Figure 5. Supply Current vs. +V 0.20 0.15 0.10 0.05 0 –0.05 – ...
Page 9
... Rev Page – TEMPERATURE (°C) Figure 13. Reference Current vs. Temperature Y+ X+ X– Y– – TEMPERATURE (°C) (X+, Y+:+V to Pin; X−, Y−: Pin to GND 125kHz SAMPLE f = 15kHz IN SNR = 68.34dB 7.5 15.0 22.5 30.0 37.5 45.0 52.5 FREQUENCY (kHz) (f =125 kHz kHz) SAMPLE INPUT AD7843 80 100 60.0 ...
Page 10
... RIPPLE FREQUENCY (kHz) CC Figure 16. AC PSRR vs. Supply Ripple Frequency Figure 16 shows the power supply rejection ratio versus V supply frequency for the AD7843. The power supply rejection ratio is defined as the ratio of the power in the ADC output at full-scale frequency f applied to the ADC V PSRR (dB log (Pf/Pfs) where the power at frequency f in ADC output ...
Page 11
... CIRCUIT INFORMATION The AD7843 is a fast, low-power, 12-bit, single-supply, A/D converter. The AD7843 can be operated from a 2 5.25 V supply. When operated from either supply supply, the AD7843 is capable of throughput rates of 125 kSPS when provided with a 2 MHz clock. The AD7843 provides the user with an on-chip track-and-hold, ...
Page 12
... AD7843 ANALOG INPUT Figure 19 shows an equivalent circuit of the analog input structure of the AD7843, which contains a block diagram of the input multiplexer, the differential input of the ADC, and the differential reference. Table 5 shows the multiplexer address corresponding to each analog input, both for the SER/ DFR bit in the control register set high and low ...
Page 13
... The other option is to operate the AD7843 in differential mode only for the touch screen and to program the AD7843 to keep the touch screen drivers on and not go into power-down (PD0 = PD1 = 1). Several conversions might be required, depending on the settling time required and the AD7843 data rate ...
Page 14
... Table PD1, PD0 Power Management Bits. These two bits decode the power-down mode of the AD7843, as shown in Table 7. derived from the voltage at the switch drivers, which is almost the same as the voltage to the touch screen. In this case, a separate reference voltage is not needed because the reference voltage to the ADC is the voltage across the touch screen ...
Page 15
... This configuration results in power-down of the device between conversions. The AD7843 only powers down between conversions. Once PD1 and PD0 are set the conversion is performed first, and the AD7843 powers down upon completion of that conversion. At the start of the next conversion, the ADC instantly powers up to full power. This means there is no need for additional delays to ensure full operation, and the very first conversion is valid. The Y− ...
Page 16
... AD7843 SERIAL INTERFACE Figure 24 shows the typical operation of the serial interface of the AD7843. The serial clock provides the conversion clock and also controls the transfer of information to and from the AD7843. One complete conversion can be achieved with 24 DCLK cycles. The CS signal initiates the data transfer and conversion process. ...
Page 17
... CS , because once CS goes low, the part detects each START bit and clocks in the control word after it on DIN. When the AD7843 is in the 12-bit conversion mode, a second START bit is not detected until seven DCLK pulses have elapsed after a control word is clocked in on DIN, ...
Page 18
... AD7843 is not as critical because settling to 8 bits is all that is required. The clock rate can be as much as 50% faster. The faster clock rate and fewer clock cycles combine to provide double the conversion rate ...
Page 19
... Table 7), when the touch screen connected to the AD7843 is touched via a pen or finger, the PENIRQ output goes low, initiating an interrupt to a microprocessor that can then instruct a control word to be written to the AD7843 to initiate a conver- sion. This output can also be enabled between conversions during power-down (see Table 7 ), allowing power- initiated only when the screen is touched ...
Page 20
... AD7843ARQ-REEL7 −40°C to +85°C 2 AD7843ARQZ −40°C to +85°C AD7843ARQZ-REEL 2 −40°C to +85°C 2 AD7843ARQZ-REEL7 −40°C to +85°C AD7843ARU −40°C to +85°C AD7843ARU-REEL −40°C to +85°C AD7843ARU-REEL7 −40°C to +85°C 3 EVAL-AD7843CB EVAL-CONTROL BRD2 4 1 Linearity error here refers to integral linearity error. ...