LINEAR MAGNETIC FIELD SENSORS
Single Clock Circuitry—
Some form of clock is needed to
trigger the set and reset pulses (Figure 6) to create the
switching signal. The circuit shown in Figure 8 can be used
to create a strong (>4Amp) pulse. The diodes, resistors,
capacitors and inverters basically create the TRS and the
TSR delays. Now a single signal (Clock) can trigger a set or
reset pulse. The minimum timing between the rising and
falling edges of Clock are determined by the 25KΩ and 1nF
time constant. That is, the minimum high and low time for
Clock is
≈25 µs.
Micro Processor—
The circuit in Figure 9 generates a strong
set/reset pulse (>4 Amp) under microprocessor control. The
5V
SET and RESET signals are generated from a
microprocessor and control the P and N channel HEXFET
drivers (IRF7105). The purpose of creating the TRS and the
TSR delays are to make sure that one HEXFET is off before
the other one turns on. Basically, a break-before-make
switching pattern. The current pulse is drawn from the 4.7
µF
capacitor. If the 5V to 20V converter is used as shown in
Figure 7, then the resultant noise and droop on the 16-20V
supply is not an issue. But if the 16-20V supply is used
elsewhere in the system, then a series dropping resistor
(≈500Ω) should be placed between the 4.7µF capacitor and
the supply.
MAX662A
2
C1+
C1-
C2-
C2+
3
0.22µF*
1
8
4
0.22µF*
1µF
Vout
6
Clock
16V
set
SHDN
7
GND
20V
1N5818
1µF
T
PW
≈
2 µsec
S/R
5V
2µF
5
Vcc
1µF
12V
-16V
reset
* Use tantalum capacitors
Figure 6—Single Clock Set/Reset Timing
Figure 7—5V to 20V Converter
+16 to 20V
4.7µF (3)
5V
25K
25K
4
1N4001
1nF
1
25K
2
10K
0.1µF
3
7
IRF7106 (1)
Clock
9
14
25K
8
3
74HC04
4
S/R strap @ 4.5Ω typ.
3A peak (min.)
HMC2003
*
0.22µF (2)
17
1
2N3904
5
6
2
1
5,6
7,8
S/R
(1) HEXFETs with
≈0.2Ω
Ron
(2) 0.22µF Tantalum or a
0.68 µF Ceramic CK06
(3) Tantalum, low R
1nF
Figure 8—Single Clock Set/Reset Pulse Circuit (1001/1002)
5V
+16 to 20V
4.7µF (1)
25K
SET
RESET
25K
3
4
16V
set
10K
0.1µF
T
RS
T
SR
IRF7106 (2)
S/R strap @ 4.5Ω typ.
3A peak (min.)
HMC2003
*
0.22µF
17
1
S/R
SET
T
PW
T
RS
≥
5 µsec
T
SR
≥
5 µsec
T
PW
≈
2 µsec
-16V
reset
2N3904
2
5,6
7,8
RESET
1
S/R
(1) Tantalum, low R
(2) HEXFETs with
≈0.2Ω
Ron
•HMC2003 contains one HMC1001 and one HMC1002; together they make the 3-axis sensor.
Three S/R straps are in serial, the total resistance is ~4.5Ω.
Figure 9—Set/Reset Circuit With Microprocessor Control (1001/1002)
9
HONEYWELL [ HONEYWELL SOLID STATE ELECTRONICS CENTER ]
