HMC10XX FAMILY
10
Figure 9—Single Clock Set/Reset Circuit(1001/1002)
S/R strap @ 4.5
typ.
3A peak (min.)
10K
1
0.22μF
4.7μF (1)
+16 to 20V
17
HMC2003
Clock
S/R
(1) Tantalum, low R
0.022μF
0.022μF
10K
ZTX605
ZTX705
S/R strap @ 4.5
typ.
3A peak (min.)
10K
1
0.22μF
+16 to 20V
17
HMC2003
Clock
S/R
0.022μF
100K
ZTX605
Clock
S/R
-16V
T
PW
≈
2 μsec
5V
reset
Figure 10—Single Clock Reset Only Circuit (1001/1002)
Low Field Measurements—When measuring 100
μ
gauss
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 7 and
8 are recommended for applications that require low noise
and high sensitivity magnetic readings.
Low Cost—For minimum field measurements above 500
μ
gauss, a less elaborate pulsing circuit can be used. In both
Figures 9 and 10, 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 10 will work.
The circuit in Figure 12 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 4.7
μ
F capacitor and a 200
ohm dropping resistor should be placed in series with the
supply to reduce noise.
Figure 11—5V Circuit for SET/RESET (1021/1022)
10K
0.1μF
1μF (1)
+5V
Clock
(1) Tantalum, low R
0.1μF
0.1μF
10K
FMMT617
FMMT717
200
9,15
14
HMC1022
8
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 11. 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.