Electronic Components Datasheet Search |
|
AD7441 Datasheet(PDF) 19 Page - Analog Devices |
|
AD7441 Datasheet(HTML) 19 Page - Analog Devices |
19 / 24 page AD7441/AD7451 Rev. D | Page 19 of 24 CS SCLK SDATA 1 10 16 1 10 16 A THIS PART IS FULLY POWERED UP WITH VIN FULLY ACQUIRED PART BEGINS TO POWER UP INVALID DATA VALID DATA tPOWER-UP Figure 31. Exiting Power-Down Mode If CS is brought high before the 10th falling edge of SCLK, the AD7441/AD7451 again go back into power-down. This avoids accidental power-up due to glitches on the CS line or an inad- vertent burst of eight SCLK cycles while CS is low. So although the device may begin to power up on the falling edge of CS, it again powers down on the rising edge of CS as long as it occurs before the 10th SCLK falling edge. Power-Up Time The power-up time of the AD7441/AD7451 is typically 1 μs, which means that with any frequency of SCLK up to 18 MHz, one dummy cycle is always sufficient to allow the device to power up. Once the dummy cycle is complete, the ADC is fully powered up and the input signal is acquired properly. The quiet time, tQUIET, must still be allowed—from the point at which the bus goes back into three-state after the dummy conversion to the next falling edge of CS. When running at the maximum throughput rate of 1 MSPS, the AD7441/AD7451 power up and acquire a signal within ±0.5 LSB in one dummy cycle, that is, 1 μs. When powering up from the power-down mode with a dummy cycle, as in Figure 31, the track-and-hold, which was in hold mode while the part was powered down, returns to track mode after the first SCLK edge the part receives after the falling edge of CS. This is shown as Point A in . Figure 31 Although at any SCLK frequency one dummy cycle is sufficient to power up the device and acquire VIN, it does not necessarily mean that a full dummy cycle of 16 SCLKs must always elapse to power up the device and acquire VIN fully; 1 μs is sufficient to power up the device and acquire the input signal. For example, when a 5 MHz SCLK frequency is applied to the ADC, the cycle time is 3.2 μs (that is, 1/(5 MHz) × 16). In one dummy cycle, 3.2 μs, the part is powered up, and VIN is acquired fully. However, after 1 μs with a five MHz SCLK, only five SCLK cycles elapse. At this stage, the ADC is fully powered up and the signal acquired. Therefore, in this case, the CS can be brought high after the 10th SCLK falling edge and brought low again after a time, tQUIET, to initiate the conversion. When power supplies are first applied to the AD7441/AD7451, the ADC can power up either in power-down mode or normal mode. For this reason, it is best to allow a dummy cycle to elapse to ensure that the part is fully powered up before attempting a valid conversion. Likewise, if the user wants the part to power up in power-down mode, then the dummy cycle can be used to ensure the device is in power-down mode by executing a cycle such as that shown in Figure 30. Once supplies are applied to the AD7441/AD7451, the power-up time is the same as that when powering up from power-down mode. It takes approxi- mately 1 μs to power up fully in normal mode. It is not necessary to wait 1 μs before executing a dummy cycle to ensure the desired mode of operation. Instead, the dummy cycle can occur directly after power is supplied to the ADC. If the first valid conversion is then performed directly after the dummy conversion, care must be taken to ensure that adequate acquisition time has been allowed. As mentioned earlier, when powering up from the power-down mode, the part returns to track mode upon the first SCLK edge applied after the falling edge of CS. However, when the ADC powers up initially after supplies are applied, the track-and- hold is already in track mode. This means (assuming one has the facility to monitor the ADC supply current) that if the ADC powers up in the desired mode of operation, a dummy cycle is not required to change mode. Thus, a dummy cycle is also not required to place the track-and-hold into track. |
Similar Part No. - AD7441 |
|
Similar Description - AD7441 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | 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 |