Zakładka z wyszukiwarką danych komponentów |
|
AD7777 Arkusz danych(PDF) 7 Page - Analog Devices |
|
AD7777 Arkusz danych(HTML) 7 Page - Analog Devices |
7 / 12 page AD7776/AD7777/AD7778 –7– REV. 0 state (as programmed by CR9), and the SAR contents are trans- ferred to the first register ADCREG1. The SAR is then reset in readiness for a new conversion. If simultaneous sampling has been requested (CR6 = 1), no change occurs in the status of the BUSY/INT output and the ADC automatically starts the second conversion. At the end of this conversion the BUSY/INT line changes state (as programmed by CR9) and the SAR contents are transferred to the second register, ADCREG2. tD* CLKIN VIN WR CHANNEL ACQUISITION 40ns TYP 40ns TYP 'HOLD' DB9 (MSB) * TIMING SHOWN FOR tD GREATER THAN 12ns Figure 6. ADC Conversion Start Timing Track-and-Hold The track-and-hold (T/H) amplifiers on the analog input(s) of the AD7776/AD7777/AD7778 allow the ADC to accurately convert an input sine wave of 2 V peak-peak amplitude up to a frequency of 189 kHz, the Nyquist frequency of the ADC when operated at its maximum throughput rate of 378 kHz. This maximum rate of conversion includes conversion time and time between conversions. Because the input bandwidth of the track- and-hold is much greater than 189 kHz, the input signal should be band limited to avoid folding unwanted signals into the band of interest. Powerdown The AD7776/AD7777/AD7778 can be placed in a powerdown mode simply by writing a logic high to location CR8 of the con- trol register. The following changes are effected immediately on writing a “1” to location CR8: • Any conversion in progress is terminated. • If a conversion is in progress, the leading edge of WR immedi- ately drives the BUSY/INT output high. • All the linear circuitry is turned off. • The REFOUT output stops being driven and is weakly (5 k Ω) pulled to analog ground. Control inputs CS, WR and RD retain their purpose while the AD7776/ AD7777/AD7778 is in powerdown. If no conversions are in progress when the AD7776/AD7777/AD7778 is placed into the powerdown modes, the contents of the ADC registers, ADCREG1 and ADCREG2, are retained during powerdown and can be read as normal. On returning to normal operating mode a new conversion (or conversions, dependent on CR6) is automatically started. On completion, the invalid conversion results are loaded into the ADC registers losing the previous valid results. In order to achieve the lowest possible power consumption in the powerdown mode special attention must be paid to the state of the digital and analog inputs and outputs: • Because each analog input channel sees a resistive divider to AGND, the input resistance of which does not change be- tween normal and powerdown modes, driving the analog input signals to 0 V or as close as possible to 0 V will minimize the power dissipated in the input signal conditioning circuitry. • Similarly, the REFIN input sees a resistive divider to AGND, the input resistance of which does not change between normal and powerdown modes. If an external reference is being used, then driving this reference input to 0 V or as close as possible to 0 V will minimize the power dissipated in the input signal conditioning circuitry. • Since the REFOUT pin is pulled to AGND via, typically, a 5 k Ω resistor, any voltage above 0 V that this output may be pulled to by external circuitry will dissipate unnecessary power. • Digital inputs CS, WR & RD should all be held at VCC or as close as possible. CLKIN should be held as close as possible to either 0 V or VCC. • Since the BUSY/INT output is actively driven to a logic high, any loading on this pin to 0 V will dissipate power. The AD7776/AD7777/AD7778 comes out of the powerdown mode when a Logic “0” is written to location CR8 of the con- trol register. Note that the contents of the other locations in the control register are retained when the device is placed in powerdown and are valid when power is restored. However, coming out of powerdown provides an opportunity to reload the complete contents of the control register without any extra instructions. |
Podobny numer części - AD7777 |
|
Podobny opis - AD7777 |
|
|
Link URL |
Polityka prywatności |
ALLDATASHEET.PL |
Czy Alldatasheet okazała się pomocna? [ DONATE ] |
O Alldatasheet | Reklama | Kontakt | Polityka prywatności | Linki | Lista producentów 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 |