Electronic Components Datasheet Search |
|
AD7898ARZ-10REEL7 Datasheet(PDF) 9 Page - Analog Devices |
|
AD7898ARZ-10REEL7 Datasheet(HTML) 9 Page - Analog Devices |
9 / 16 page –9– REV. A AD7898 Figure 2 shows the analog input section for the AD7898-10 and AD7898-3. The analog input range of the AD7898-10 is ±10 V into an input resistance of typically 30 kΩ. The analog input range of the AD7898-3 is ±2.5 V into an input resistance of typically 6 k Ω. This input is benign, with no dynamic charg- ing currents, as the resistor stage is followed by a high input impedance stage of the track/hold amplifier. For the AD7898-10, R1 = 30 k Ω, R2 = 7.5 kΩ and R3 = 10 kΩ. For the AD7898-3, R1 = R2 = 6.5 k Ω and R3 is open circuit. For the AD7898-10 and AD7898-3, the designed code transi- tions occur midway between successive LSB values (i.e., 1/2 LSB, 3/2 LSBs, 5/2 LSBs . . .). Output coding is twos complement binary with 1 LSB = FS/4096. For the AD7898-10 1 LSB = 20/ 4096 = 4.88 mV. For the AD7898-3 1 LSB = 5/4096 = 1.22 mV. The ideal input/output coding for the AD7898-10 and AD7898-3 is shown in Table I. Table I. Ideal Input/Output Code Table for the AD7898-10/ AD7898-3 Digital Output Analog Input l Code Transition +FSR/2 – 3/2 LSB 2 011 . . . 110 to 011 . . . 111 +FSR/2 – 5/2 LSBs 011 . . . 101 to 011 . . . 110 +FSR/2 – 7/2 LSBs 011 . . . 100 to 011 . . . 101 AGND + 3/2 LSB 000 . . . 001 to 000 . . . 010 AGND + 1/2 LSB 000 . . . 000 to 000 . . . 001 AGND – 1/2 LSB 111 . . . 111 to 000 . . . 000 AGND – 3/2 LSB 111 . . . 110 to 111 . . . 111 –FSR/2 + 5/2 LSBs 100 . . . 010 to 100 . . . 011 –FSR/2 + 3/2 LSBs 100 . . . 001 to 100 . . . 010 –FSR/2 + 1/2 LSB 100 . . . 000 to 100 . . . 001 NOTES 1FSR is full-scale range = 20 V (AD7898-10) and = 5 V (AD7898-3) with REF IN = 2.5 V. 21 LSB = FSR/4096 = 4.883 mV (AD7898-10) and 1.22 mV (AD7898-3) with REF IN = 2.5 V. SOURCE IMPEDANCE – –70 –75 –85 10k 100 10 –60 –65 –80 –90 1k f IN = 10k f IN = 50k f IN = 25k f IN = 110k Figure 3. THD vs. Source Impedance for Various Analog Input Frequencies Figure 3 shows a graph of THD versus source impedance for different analog input frequencies when using a supply voltage of 5 V, VDRIVE of 5 V, and sampling at a rate of 220 kSPS. Source impedance has a minimal effect on THD because of the resistive ladder structure of the input section of the ADC. Figure 4 shows a graph of THD versus Analog input frequency for vari- ous supply voltages while sampling at 220 kSPS. INPUT FREQUENCY – kHz –20 –40 –80 1000 10 0 –10 –60 –100 100 –30 –70 –50 –90 VDD = VDRIVE = 4.75V VDD = VDRIVE = 5.25V VDD = 5.0V, VDRIVE = 3.0V Figure 4. THD vs. Analog Input Frequency for Various Supply Voltages Acquisition Time The track-and-hold amplifier enters its tracking mode on the falling 14th SCLK edge after the CS falling edge for Mode 1 operation. The time required for the track-and-hold amplifier to acquire an input signal will depend on how quickly the 9.1 pF sampling capacitance is charged. With zero source impedance on the analog input, two SCLK cycles plus tQUIET will always be sufficient to acquire the signal to the 12-bit level. With an SCLK frequency of 3.7 MHz, the acquisition time would be 2 × (270 ns) + t QUIET. The acquisition time required is calculated using the following formula: tACQ = 10 × (RC) where R is the resistance seen by the track-and-hold amplifier looking back on the input e.g., for AD7898-10 R = 3.75 k Ω and for AD7898-3 R = 3.25 k Ω. The sampling capacitor has a value of 9.1 pF. Theoretical acquisition times would be 340 ns for AD7898-10, and 295 ns for AD7898-3. These theoretical values do not include tQUIET or track propagation delays in the part, typical values would be 520 ns for the AD7898-10 and 450 ns for the AD7898-3. |
Similar Part No. - AD7898ARZ-10REEL7 |
|
Similar Description - AD7898ARZ-10REEL7 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |