LINEAR MAGNETIC FIELD SENSORS
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
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.
the supply.
MicroProcessor—ThecircuitinFigure9generatesastrong
set/resetpulse(>4Amp)undermicroprocessorcontrol.The
MAX662A
2
1
3
4
C1+
C1-
C2-
0.22µF*
0.22µF*
1µF
5V
C2+
Clock
8
7
SHDN
GND
16V
set
20V
6
Vout
TPW ≈ 2 µsec
5V
1N5818
12V
1µF
5
Vcc
S/R
2µF
1µF
reset
-16V
* Use tantalum capacitors
Figure 6—Single Clock Set/Reset Timing
Figure 7—5V to 20V Converter
+16 to 20V
25K
4.7µF (3)
5V
74HC04
25K
3
25K
14
7
S/R strap @ 4.5Ω typ.
Clock
9
8
3
4
3A peak (min.)
4
HMC2003
*
1nF
0.1µF
1N4001
10K
17
1
1
5
2
6
0.22µF (2)
5,6
7,8
2N3904
25K
2
S/R
1
1nF
(1) HEXFETs with ≈0.2Ω Ron
(2) 0.22µF Tantalum or a
0.68 µF Ceramic CK06
(3) Tantalum, low R
Figure 8—Single Clock Set/Reset Pulse Circuit (1001/1002)
+16 to 20V
5V
4.7µF (1)
SET
25K
25K
3
RESET
S/R strap @ 4.5Ω typ.
T
RS
TSR
3A peak (min.)
4
16V
HMC2003
*
set
0.1µF
10K
17
1
0.22µF
SET
S/R
5,6
7,8
2N3904
T
PW
2
T
T
RS ≥ 5 µsec
SR ≥ 5 µsec
RESET
S/R
reset
-16V
1
(1) Tantalum, low R
(2) HEXFETs with ≈0.2Ω Ron
T
PW ≈ 2 µsec
•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 ]
