U211B-XFPG3Y ATMEL Corporation, U211B-XFPG3Y Datasheet - Page 6

• Manufacturer Part Number: U211B-XFPG3Y
• Description: Phase Control IC with Overload Limitation for Tacho Applications
• Manufacturer: ATMEL Corporation

7. Frequency-to-voltage Converter
6
U211B
The internal frequency-to-voltage converter (f/V converter) generates a DC signal on pin 10
which is proportional to the rotational speed, using an AC signal from a tacho generator or a light
beam whose frequency is in turn dependent on the rotational speed. The high-impedance input
pin 8 compares the tacho voltage to a switch-on threshold of typically -100 mV. The switch-off
threshold is -50 mV. The hysteresis guarantees very reliable operation even when relatively sim-
ple tacho generators are used.
The tacho frequency is given by:
f
where:
The converter is based on the charge pumping principle. With each negative half-wave of the
input signal, a quantity of charge determined by C
C
transfer voltage of V
k = G
The analog output voltage is given by
V
The values of C
mum output voltage V
approximately 6.7 k . To obtain good linearity of the f/V converter, the time constant resulting
from R
the highest possible input frequency. The amount of remaining ripple on the output voltage on
pin 10 is dependent on C
The ripple V
then also be reduced.
The value of this capacitor should be chosen to fit the particular control loop where it is going to
be used.
G
V
O
6
=
i
O
at the converter output on pin 10. The conversion constant is determined by C
= k
I
------ -
I
----- -
60
10
n
9
i
=
i
and C
G
------------------------------------ -
=
C
f
p (Hz)
i
5
8.3
V
C
O
5
R
ch
should be considerably less (1/5) than the time span of the negative half-cycle for
6
can be reduced by using larger values of C
6
5
and C
C
V
ch
ch
5
, R
n
p
6
O
6
5
must be such that for the highest possible input frequency, the maxi-
does not exceed 6 V. While C
, C
(pin 10) and the internally adjusted charge transfer gain.
6
and the internal charge amplification.
= Revolutions per minute
= Number of pulses per revolution
5
is internally amplified and then integrated by
5
6
. However, the increasing speed will
is charging up, the R
4752B–INDCO–09/05
i
5
, its charge
on pin 9 is