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Data Sheet

AD7293

Rev. B | Page 73 of 78

Table 114. Current Sensor Integration Time

Code

Gain

Clocks

Typical Integration Time (µs)

0000

6.25

440

17.6

0001

12.5

650

26.0

0010

18.75

860

34.4

0011

1070

42.8

0100

37.5

1490

59.6

0101

1910

76.4

0110

2750

110.0

0111

100

3590

143.6

1000

200

6950

278.0

1001

400

13670

546.8

1010

781.25

26480

1059.2

Table 115. Temperature Sensor Integration time

Channel

Clocks

Typical Integration Time (µs)

TSENSEINT

30523

1220.92

TSENSED0

60987

2439.48

TSENSED1

60987

2439.48

Each current sense channel has its own integrator, whereas

there is only one integrator for all three temperature channels.

Therefore, temperature inputs that are enabled are measured

sequentially. This means that, for example, if all are enabled, the

update time is (1220.92 µs + 2 × 2439.48 µs) = 6099.88 µs

Conversion and Integration Timing Example 1

Enable three of the current sense channels with a gain of 6.25.

All three integrations start as soon as the enable register is

written to. After 17.6 µs, all three voltages are ready to be

converted by the ADC. The ISENSE0 channel is converted first,

while the ISENSE1 channel and the ISENSE2 channel are held in the

queue. After the ISENSE0 conversion is complete, the ISENSE0

amplifier is released to start a new integration, and the ADC

moves on to convert the ISENSE1 voltage.

The AD7293 settles into a routine, converting the three ISENSEx

channels, each with an update time of (17.6 µs + 4.2 µs) = 21.8 µs.

See Figure 57 for more details.

Conversion and Integration Timing Example 2

In this example, in addition to the three current sense channels,

three monitor channels are also enabled, as shown in Figure 58.

The ADC is busy all the time; therefore, the time it takes to

complete a cycle of conversions is the sum of all the conversion

times: (4.2 µs × 3 + 4.0 µs × 3) = 24.6 µs.

If the temperature sensor is also enabled, when the output of the

temperature sensor is ready (once every 1 ms to 2 ms depending

on which channels are selected), the ADC sequencer waits for

its turn in the sequence before initiating a conversion on the

particular TSENSEx channel. The combination of conversions

increases the duration of that particular cycle from 24.6 µs to

(24.6 µs + 2.3 µs) = 26.9 µs in this example.

Digital Filtering

A digital filter is available on the ADC channels. The digital

filter consists of a simple low-pass filter function to help reduce

unwanted noise on dc signals. This low-pass filter has a −3 dB

cutoff frequency of

400

3dB

≈

−

where fS is the sample frequency. The sample frequency depends

on the type of channel, how many other channels are enabled,

and whether it is in background mode or command mode (for

example, if the internal temperature sensor channel is enabled

alone, the update period is 1220.92 µs typically, which is close to

fS ≈ 819 Hz). If VIN0, VIN1, VIN2, and VIN3 are also enabled in

background mode, a conversion then takes place on VIN0 every

9.2 µs (2.3 µs × 4), meaning fS ≈ 1 ÷ 9.2 µs ≈ 108.7 kHz. To

avoid aliasing of high frequencies at the input, use an antialias

filter to reject input frequencies above fS/2.

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