7.3.4 Digital Output

A differential input signal of 0 V ideally produces a stream of ones and zeros that are high 50% of the time.

A differential input of 1 V produces a stream of ones and zeros that are high 90% of the time. With 16 bits of

resolution, that percentage ideally corresponds to code 58982. A differential input of –1 V produces a stream

of ones and zeros that are high 10% of the time and ideally results in code 6553 with 16-bit resolution. These

input voltages are also the specified linear range of the AMC3336. If the input voltage value exceeds this range,

the output of the modulator shows nonlinear behavior as the quantization noise increases. The output of the

modulator clips with a stream of only zeros with an input less than or equal to –1.25 V or with a stream of only

ones with an input greater than or equal to 1.25 V. In this case, however, the AMC3336 generates a single 1

(if the input is at negative full-scale) or 0 (if the input is at positive full-scale) every 128 clock cycles to indicate

proper device function (see the Output Behavior in Case of a Full-Scale Input section for more details). Figure

7-4 shows the input voltage versus the output modulator signal.

Modulator Output

+ FS (Analog Input)

– FS (Analog Input)

Analog Input

Figure 7-4. Analog Input vs Modulator Output

The density of ones in the output bitstream for any input voltage value can be calculated using Equation 1 (with

the exception of a full-scale input signal, as described in the Output Behavior in Case of a Full-Scale Input

section):

IN

Clipping

Clipping

V

V

2 V

u

(1)

7.3.4.1 Output Behavior in Case of a Full-Scale Input

generates a single one or zero every 128 bits at DOUT, depending on the actual polarity of the signal being

sensed. In this way, detecting a valid full-scale input signal and differentiating it from a missing high-side supply

is possible on the system level.

DOUT

CLKIN

127 CLKIN cycles

127 CLKIN cycles

–1.25 V

DOUT

Figure 7-5. Full-Scale Output of the AMC3336

7.3.4.2 Output Behavior in Case of a High-Side Supply Failure

The AMC3336 provides a fail-safe output that ensures that the output DOUT of the device offers a constant

bitstream of logic 0's in case the integrated DC/DC converter output voltage is below the undervoltage detection

threshold. See the Diagnostic Output section for more information.

AMC3336

SBASA70 – APRIL 2021

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