ADA4255ACPZ-R7 datasheet(27/64 Pages) AD

27 / 64 page

Data Sheet

ADA4255

THEORY OF OPERATION

analog.com

Rev. 0 | 27 of 64

Figure 87. External EMI Filter Improves Noise Rejection

INPUT AMPLIFIER

The ADA4255 input amplifier operates on internally generated high

voltage power supplies, VDDH and VSSH. On-chip charge pumps

are used by the ADA4255 to generate VDDH and VSSH from the

VDDCP supply.

The input amplifiers are internally monitored for clipping due to ex-

cessive signal swing. If excessive output swing is detected by any

part of the input amplifier (A1 to A8 in Figure 85), the INPUT_ERR

flag trips. If INPUT_ERR is tripped for more than 200 μs, the gain

settings in the GAIN_MUX register are reset to their default values

and the G_RST flag trips. By default, the G_RST event sets all

gain bits in the GAIN_MUX register to their default values, which

may also result in a MM_CRC_ERR. The gain reset function can be

disabled via the G_RST_DIS bit.

OUTPUT AMPLIFIER

The ADA4255 features a fully differential output amplifier running

from the dedicated low voltage supplies, AVDD and AVSS. Use

AVDD and AVSS in a single-supply configuration. By running the

output amplifier on low voltage supplies, circuitry connected to the

output of the ADA4255 is inherently protected. The common-mode

output voltage is set by the VOCM input voltage. VOCM has a high

input impedance and is not biased internally. VOCM also features a

29 MHz EMI filter to minimize EMI interference. Typically, VOCM is

biased to midsupply through a voltage divider between AVDD and

AVSS to allow the widest swing on the output. The output amplifier

can be set to three different scaling gains via G4 or G5: 1 V/V,

1.25 V/V, or 1.375 V/V. On power-up or soft reset, the output

amplifier scaling gain defaults to 1 V/V. The output amplifier is

monitored for clipping due to excessive signal swing. When the

output saturates to either supply, the OUTPUT_ERR flag trips.

The differential output stage of the ADA4255 allows the device

to be directly connected to high precision ADCs, such as the

AD7768 and the AD4007. When making such a connection, it

is recommended to use a low-pass filter to minimize noise and

aliasing, as shown in Figure 88. The LTC6363 is configured as a

3-pole, low-pass filter with a cutoff frequency of 40 kHz.

Figure 88. Simple Output Filter Preventing Aliasing and Filters Switching

Noise

Figure 89. LTC6363 Used as a Low-Pass Filter and Driver

ADA4255ACPZ-R7 データシート(PDF) 27 Page - Analog Devices

ADA4255ACPZ-R7 データシート(HTML) 27 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

データシートダウンロード