MXD2020GL datasheet(6/7 Pages) ETC

6 / 7 page

MEMSIC MXD2020GL/ML/NL/HL

Page 6 of 7

2002.08.29.1

CONVERTING THE DIGITAL OUTPUT TO AN

ANALOG OUTPUT

The PWM output can be easily converted into an analog

output by integration. A simple RC filter can do the

conversion. Note that that the impedance of the circuit

following the integrator must be much higher than the

impedance of the RC filter. Reference figure 4 for an

example.

1uF

DOUT

AOUT

10K

MEMSIC

Accel.

Figure 4: Converting the digital output to an analog voltage

POWER SUPPLY NOISE REJECTION

Two capacitors and a resistor are recommended for best

rejection of power supply noise (reference Figure 5 below).

The capacitors should be located as close as possible to the

device supply pins (VDA, VDD). The capacitor lead length

should be as short as possible, and surface mount capacitors

are preferred. For typical applications, capacitors C1 and

C2 can be ceramic 0.1 µF, and the resistor R can be 10 Ω.

In 5V applications where power consumption is not a

concern, maximum supply noise rejection can be obtained

by significantly increasing the values of C1, C2 and R. For

example, C1 = C2 = 0.47 µF and R = 270 Ω will virtually

eliminate power supply noise effects.

MEMSIC

Accelerometer

VDA

VDD

V SUPPLY

Figure 5: Power Supply Noise Rejection

PCB LAYOUT AND FABRICATION SUGGESTIONS

1. The Sck pin should be grounded to minimize noise.

2. Liberal use of ceramic bypass capacitors is

recommended.

3. Robust low inductance ground wiring should be used.

4. Care should be taken to ensure there is “thermal

symmetry” on the PCB immediately surrounding the

MEMSIC device and that there is no significant heat

source nearby.

5. A metal ground plane should be added directly beneath

the MEMSIC device. The size of the plane should be

similar to the MEMSIC device’s footprint and be as

thick as possible.

6. Vias can be added symmetrically around the ground

plane. Vias increase thermal isolation of the device

from the rest of the PCB.

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