Data Sheet
LINEAR MAGNETIC FIELD SENSORS
10
Figure 10—Single Clock Set/Reset Circuit (1001/1002)
Figure 11—Single Clock Reset Only Circuit (1001/1002)
Low Field Measurements—
When measuring 100 µgauss
resolution or less, the permalloy film must be completely
set, or reset, to insure low noise and repeatable
measurements. A current pulse of 4 amps, or more, for just
a couple microseconds will ensure this. The circuits in
Figures 8 and 9 are recommended for applications of
HMC1001/2 that require low noise and high sensitivity
magnetic readings.
Low Cost—
For minimum field measurements above 500
µgauss, a less elaborate pulsing circuit can be used. In both
Figures 10 and 11, the pulse signal is switched using lower
cost Darlington transistors and fewer components. This circuit
may have a more limited temperature range depending on the
quality of transistors selected. If accuracy is not an issue and
cost is, then the reset only circuit in Figure 11 will work.
The circuit in Figure 13 generates a strong set/reset pulse
under a microprocessor clock driven control. A free running
555 timer can also be used to clock the circuit. The SET
current pulse is drawn from the 1 µF capacitor and a 200
ohm dropping resistor should be placed in series with the
supply to reduce noise.
For any magnetic sensor application, if temperature drift is
not an issue, then the reset pulse need only be occasionally
applied. This will save power and enable the use of digital
filtering techniques as shown in Figure 12. Circumstances
for a reset pulse would be 1) power on or, 2) field over/
under range condition. Any other time the sensor should
perform normally.
*The HMC2003 has 3-axis S/R straps in series.
These are the HMC1001 and HMC1002 sensors.
Figure 12—5V Circuit for SET/RESET (1021/1022)
S
/
R
strap
@
4.5Ω typ.
3A peak (min.)
10
K
1
0.22µ
F
4.7µ
F(
1
)
+16 to 20V
17
HMC
2003
*
Clock
S/R
(
1
)T
anta
l
um,
l
ow
R
0.022µ
F
0.022µ
F
10
K
ZTX
605
ZTX
705
10K
0.1µF
1µF (1)
+5V
Clock
(1) Tantalum, low R
0.1µF
0.1µF
10K
FMMT617
FMMT717
200
9,1514
HMC1022
8
S
/
R
strap
@
4.5Ω typ.
3A peak (min.)
10
K
1
0.22µ
F
+16 to 20V
17
HMC
2003
Clock
S/R
0.022µ
F
100
K
ZTX
605
Clock
S/R
-16
V
TPW ≈ 2 µsec
5
V
reset
*
1µF (1)
0.1µF
0.1µF
0.1µF