DATA SHEET
HAL856
4. Application Notes
4.1. Measurement of a PWM Output Signal
Micronas recommends the following application cir-
cuits for HAL856.
In case that the PWM output mode is activated, the
magnetic field information is coded in the duty cycle of
the PWM signal. The duty cycle is defined as the ratio
between the high time “s” and the period “d” of the
PWM signal (see Fig. 4–3).
It is recommended to connect a ceramic 4.7 nF capac-
itor between ground and the supply voltage. Further-
more it is recommended to place a 30 Ω resistor in the
supply voltage line.
Note: The PWM signal is updated with the falling
edge. Hence, for signal evaluation, the trigger-
level must be the falling edge of the PWM sig-
nal.
System side
= 8 V...18 V
Sensor side
V
battery
R
= 30 Ω
P
V
DD
1
2
3
Out
C
= 4.7 nF
GND
d
P
s
IDD,high
R
= 120 Ω
sense
Fig. 4–1: Application circuit HAL856
IDD,low
time
Update
To use the HAL856 over the full temperature and sup-
ply voltage range and with all available high current
levels, Micronas recommends using a current mirror or
special interface devices. Fig. 4–2 shows an example
using a current mirror.
Fig. 4–3: Definition of PWM signal
4.2. Measurement of a Biphase-M Output Signal
In order to read the Biphase-M signal Micronas sug-
gests to use a port interrupt which is configured to gen-
erate interrupts with both the falling and rising edge of
the incoming signal.
V
DD HAL856
1
3
4.7 nF
With each interrupt a timer shall be read out. The first
two edges (SYNC bit) define the bit time tp0. Compar-
ing subsequent timer readouts with tp0 successively
decodes the Biphase-M pattern.
V
Ref
2
R
R
µC
T1
T2
Fig. 4–2: Application circuit with current mirror
A special interface device could be, for example, the
MAXIM MAX9921 (Dual, 2-Wire Hall-Effect Sensor
Interface with Diagnostics) chip. With these interface
ICs, together with HAL856, a single-wire interface is
possible.
Note: The third sensor pin should be floating or con-
nected to the GND line.
Micronas
March 23, 2010; DSH000142_002EN
29
MICRONAS [ MICRONAS ]
