HMC1053【PDF 8/11 页】SENSOR MAGNETIC 3-AXIS 16-PLCC

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Sheet目录61

4页 5页 6页 7页 [8页]9页 10页 11页

HMC1051/HMC1052/HMC1053

8 www.honeywell.com

Set/Reset Circuit Notes

The above set/reset circuit in Figure 1using the IRF7507

dual complementary MOSFETs is shown in detail by Figure

2 in its H-bridge driven configuration. This configuration is

used primarily in battery operated applications were the

500mA nominal set/reset pulsed currents can be best

obtained under low voltage conditions.

The 200-ohm resistor trickle charges the 1uf supply

reservoir capacitor to the Vcc level, and isolates the battery

from the high current action of the capacitors and MOSFET

switches. Under conventional logic states one totem pole

switch holds one node of the 0.1uf capacitor low, while the

other switch charges Vcc into the capacitors opposite node.

At the first logic change, the capacitor exhibits almost a

twice Vcc flip of polarity, giving the series set/reset strap

load plenty of pulse current. A restoring logic state flip uses

the 0.1uf capacitors stored energy to create a second nearly

equal but opposite polarity current pulse through the

set/reset strap.

For operation at normal 3.3 or 5-volt logic levels, a single complementary MOSFET pair can be used in a single ended

circuit shown in Figure 4. Other complementary MOSFET pairs can be used with the caution that the chosen devices

should have less than 0.5 ohms ON resistance and be able to handle the needed supply voltages and set/reset currents.

Note that even a 1Hz rate of set/reset function draws an

average current of less than 2 microamperes.

Magnetic Field Detection

For simple magnetic field sensing applications such

Magnetic Anomaly Detectors (MADs) and Magnetometers,

a similar circuit to the compass application can be

implemented using one, two, or three magnetic sensors. In

the example circuit in Figure 5, a HMC1051Z sensor bridge

is used with a low voltage capable dual op-amp to detect

sufficient intensity of a magnetic field in a single direction.

Uses of the circuit include ferrous object detection such as

vehicle detection, a sniffer for currents in nearby

conductors, and magnetic proximity switching. By using two

or three sensor circuits with HMC1051, HMC1052, or

HMC1053 parts, a more omni-directional sensing pattern

can be implemented. There is nothing special in choosing the resistors for the differential op-amp gain stages other than

having like values (e.g. the two 5k and the 500k resistors) matched at 1% tolerance or better to reject common-mode

interference signals (EMI, RFI). The ratio of the 500k /5k resistors sets the stage gain and can be optimized for a

specific purpose. Typical gain ratios for compass and magnetometer circuits using the HMC105X family, range from 50 to

500. The choice of the 5k value sets impedance loading seen by the sensor bridge network and should be about 4 kilo-

ohms or higher for best voltage transfer or matching. Note that Figure 5 also shows an alternative set/reset strap driver

circuit using two darlington complentary paired BJTs as electronic switches.

I R F 7 5 0 9 ( P )

I R F 7 5 0 9 ( N )

V c c

2 0 0

1 f

V s r

I R F 7 5 0 9 ( P )

I R F 7 5 0 9 ( N )

V s r

s e t / r e s e t

_ s e t / r e s e t

. 1 f

R s e t / r e s e t

I R F 7 5 0 9 ( P )

I R F 7 5 0 9 ( N )

V c c

2 0 0

1 f

V s r

I R F 7 5 0 9 ( P )

I R F 7 5 0 9 ( N )

V s r

s e t / r e s e t

_ s e t / r e s e t

. 1 f

R s e t / r e s e t

Figure 3

H-Bridge Driver

Figure 4

Single-Ended Driver

I R F 7 5 0 9 ( P )

I R F 7 5 0 9 ( N )

V c c

2 0 0

1 f

V s r

s e t / r e s e t

. 1 f

R s e t / r e s e t

I R F 7 5 0 9 ( P )

I R F 7 5 0 9 ( N )

V c c

2 0 0

1 f

V s r

s e t / r e s e t

. 1 f

R s e t / r e s e t

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