MPXM2202GS datasheet(122/670 Pages) MOTOROLA

122 / 670 page

AN1632

2–86

Motorola Sensor Device Data

www.motorola.com/semiconductors

• Connection to the A/D on an MCU

When using the accelerometer with the analog to digital

converter on an MCU, it is important to connect the supply

and ground pins of the accelerometer and the VRH and VRL

pins of the MCU to the same supply and ground traces,

respectively. This will maximize the ratiometricity of the

system by avoiding voltage differences that may result

from trace impedances.

Figure 2 shows the recommended supporting circuitry for

operating the new accelerometer. Part (a) shows the16 pin

DIP package version, the MMA1201P, while part (b) shows the

6 pin Wingback package version, the MMA2200W. For the

MMA1201P, pins 1, 2, 3, 6, 14, 15, and 16 have no internal

connections, and pins 9 through 13 are used for calibration

and trimming in the factory. These pins should all be left un-

connected. For the MMA2200W, pins 1 and 4, and the wings

(supporting pins) should be left unconnected.

VSS

VDD

VOUT

MMA2200W

VCC

LOGIC INPUT

OUTPUT SIGNAL

(b)

VSS

VDD

VOUT

MMA1201P

VCC

0.1 F

LOGIC INPUT

OUTPUT SIGNAL

(a)

0.01 F

0.1 F

0.01 F

Figure 2. Accelerometers with Recommended Supporting Circuitry

11 TRIM 3

PSRR AND ALIASING GAIN MODEL

Although the operational amplifiers in the MMA1201P’s

control ASIC have a high power supply rejection ratio with a

fairly wide bandwidth, because the accelerometer is in reality

a sampled analog system using switched capacitor technol-

ogy, it is possible that when powered with a switching power

supply, noise from the supply will appear in the output signal.

This is known as aliasing, the result being a signal with fre-

quency equal to the difference between the frequency of the

power supply noise and the accelerometer’s sampling fre-

quency. Aliasing gain is defined as the power of the output

signal relative to an injected sinusoid on the VDD line powering

the accelerometer.

Typical switching power supplies have operating frequen-

cies between 50 and 100 kHz. The operating frequency of the

accelerometer’s switching capacitor circuitry is roughly 65

kHz. Should the fundamental frequency of the switching

power supply, or its harmonics, fall within 400 Hz of the ASIC’s

fundamental frequency (or its harmonics), then any noise

present in the power supply will be aliased into the passband

of the accelerometer. As will be explained later in this section,

there are several simple ways to avoid aliasing.

As shown in Figure 1, there are many different signal pro-

cessing stages in the ASIC. As a result, the aliasing gain

characteristics of the part are a little bit more complex than

explained in the previous paragraph. An analysis was done to

characterize the worst case aliasing gain of the accelerome-

ter. Devices from three production lots were used. The parts

were tested at 105

_C with 5.25 V on VDD. The gain code was

set to the nominal value plus 4

σ. Thus, the parts had a sensi-

tivity that was approximately twice that of standard parts.

Figure 3, shows a plot of the aliasing gain model that was

developed. The model is based on the worst case results;

typical parts should perform much better having much lower

aliasing gain.

The following equation was used to fit the data and generate

the model:

Aliasing Gain = 1.6965 + 0.0029 * Freq. (kHz) + HRC1

* Freq. (kHz) + HRC2

where HRC1 and HRC2 are coefficients used in the model.

Their values vary for each harmonic. Figure 4 lists the values

of HRC1 and HRC2 for the fundamental frequency and the first

5 harmonics.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MPXM2202GS 数据表(PDF) 122 Page - Motorola, Inc

MPXM2202GS 数据表(HTML) 122 Page - Motorola, Inc

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 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载