MMA7455 Parallax, Inc., MMA7455 Datasheet - Page 3

• Manufacturer Part Number: MMA7455
• Description: Mma7455 3-axis Accelerometer Module
• Manufacturer: Parallax, Inc.

Operating Conditions
Notes:
Principle of Operation
The Freescale MMA7455L is a surface-machined Micro Electro-mechanical System (MEMS) formed by
masking and etching semiconductor materials. It can be visualized as a very small mass suspended in
the center of the device by tiny springs. When an acceleration is applied to the device, the mass deflects
along one or more axes inside the device. Built-in circuitry constantly measures the amount of deflection
along each axis and translates it into acceleration data. Then the data becomes available to be read by
an external microcontroller. For more detailed information refer to the Freescale MMA7455L product
documentation.
I/O Level Shifting
Part of what makes this 3-Axis Accelerometer module so useful is its wide power supply and I/O voltage
compatibility range of 2.5 V to 5.5 V. The MMA7455L device operates over a supply voltage range of 2.4
V to 3.6 V; so to make it compatible with devices operating up to 5.5 V, a 3.3 V Low Dropout (LDO)
voltage regulator was installed, as well as two types of level shifting circuits. This allows the device to
operate and communicate over the full voltage supply range.
For the DATA pin, a bi-directional level shifting IC is used to translate the lower I/O voltage of the
MMA7455L to the possibly higher voltage used by an externally connected device. This particular level
shifter has built-in pull-up resistors to each supply rail so it can be driven by open drain outputs for I
but can also be driven low/high for SPI protocol. Additionally, it automatically detects the direction of
data flow and switches the output drivers accordingly.
The CLK and CS pins operate exclusively as inputs, so simpler and cheaper level shifting circuits can be
used. Only a resistor and Schottky diode are required for each pin. See the Module Schematic section
for details. When an external device drives the CLK or CS pin low, the I/O pin on the MMA7455L is pulled
Copyright © Parallax Inc.
Parameter
V
Supply Current
Operating Temperature Range
Output Data (Measurement) Rate
Sensitivity
0g Output Signal
SPI Clock Frequency
IN
1.
2.
3.
4.
5.
Operational (Sensing) Mode
Operational Mode & Pins Loaded
Standby Mode
Data Rate is 125 Hz when 62.5 Hz BW selected
Data Rate is 250 Hz when 125 Hz BW selected
Supply Voltage
Supply current measured flowing into VIN pin. V
Operational Mode current measured with MMA7455L device placed in Measurement Mode and CLK, DATA, and CS pins
disconnected.
Operation Mode & Pins Loaded is measured as worst-case current draw with CLK, DATA, and CS pins all connected to
ground; INT1 and INT2 pins left disconnected.
Standby Mode current measured with MMA7455L device placed in standby mode and CLK and DATA lines left high
(connected to V
Values taken from Freescale Semiconductor MMA7455L device specifications.
(5)
±2g range, 8-bit
(1)
(5)
(1)(4)
±2g range, 8-bit
IN
) or disconnected. Value may be higher if these lines are loaded.
(1)(2)
MMA7455 3-Axis Accelerometer Module (#28526)
(1)(3)
IN
= 5.5 V
Min
-40
-21
2.5
58
--
--
--
--
--
--
3.3 – 5
Typ
437
125
250
<3
26
25
64
0
4
v1.1 9/24/2009 Page 3 of 6
Max
555
5.5
4.3
42
85
70
21
--
--
--
count/g
count
MHz
Unit
mA
μA
μA
Hz
Hz
°C
V
2
C;