AS5043 datasheet(13/26 Pages) AMSCO

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AS5043 Programmable 360° Magnetic Angle Encoder

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12.3 Digital-to-Analog Converter (DAC)

The DAC has a resolution of 10bit (1024 steps) and can

be configured for the following options

Internal or external reference

The default DAC reference is the voltage at pin #16

(VDD5V) divided by 2 (see Figure 14). Using this

reference, a system that has an output voltage

ratiometric to the supply voltage can be built.

Optionally, an external reference source, applied at pin#9

(DACref) can be used. This programming option is useful

for applications requiring a precise output voltage that is

independent of supply fluctuations, for current sink

outputs or for applications with a dynamic reference, e.g.

attenuation of audio signals.

0-100% or 10-90% full scale range

The reference voltage for the DAC is buffered internally.

The recommended range for the external reference

voltage is 0.2V to (VDD3V3 -0.2)V.

The DAC output voltage will be switched to 0V, when the

magnetic field is out of range, when the MagInc and

MagDec indicators are both =1 and the MagRngn-pin (#1)

will go low.

The default full scale output voltage range is 0-

100%*VDD5V. Due to limitations in the output stage of

an OP-Amp buffer, it cannot drive the output voltage from

0-100% rail-to-rail. Without load, the minimum output

voltage at 0° will be a few millivolts higher than 0V and

the maximum output voltage will be slightly lower than

VDD5V . With increasing load, the voltage drops will

increase accordingly.

As a programming option, an output range of 10-

90%*VDD5V can be selected. In this mode, there is no

saturation at the upper and lower output voltage limits

like in the 0-100% mode and it allows failure detection as

the output voltage will be outside the 10-90% limits,

when the magnetic field is in the “red” range (Vout=0V,

see Table 3) or when the supply to the chip is interrupted

(Vout=0V or VDD5V).

The unbuffered output of the DAC is accessible at pin

#10 (DACout). This output must not be loaded.

12.4 OP-AMP stage

The DAC output is buffered by a non-inverting Op-Amp

stage. The amplifier is supplied by VDD5V (pin #16) and

can hence provide output voltages up to 5V.

By allowing access to the inverting input of the Op-Amp

and with the addition of a few discrete components it can

be configured in many ways, like high current buffer,

current sink output, adjustable angle range, etc...

Per default, the gain of the Op-Amp must be set by two

external resistors (see Figure 14). Optionally, the fixed

internal gain setting (2x) may be programmed by OTP,

eliminating the need for external resistors.

12.4.1 Output Noise

The Noise level at the analog output depends on two

states of the digital angular output:

the digital angular output value is stable

In this case, the output noise is the figure given

as Vnoise in paragraph 19.3.6. Note that the

noise level is given for the default gain of 2x

For other gains, it must be scaled accordingly.

the digital output is at the edge of a step

In this case, the digital output may jitter

between two adjacent values. The rate of jitter

is specified as transition noise (parameter TN

in paragraph 19.5). The resulting output noise

is calculated by:

OPAMP

noise

Vout

noise

VDD

360

∗

where:

Vnoise, Vout

= noise level at pin Vout in Vrms

= transition noise (see 19.5 in °rms)

VDD5V

= Supply voltage VDD5V in V

Vnoise,OPAMP

= noise level of OPAMP

(paragraph 19.3.6) in Vrms

12.5 Application Examples

See Application Note AN5043-10 for AS5043 Application

Examples.

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