U211B ATMEL Corporation, U211B Datasheet - Page 5

• Manufacturer Part Number: U211B
• Description: as U209B + Foldback
• Manufacturer: ATMEL Corporation

C
current of typically 45 mA (t
charging current to approx. 4 mA, the slope of the
charging function is substantially reduced so that the
rotational speed of the motor only slowly increases. The
charging current then increases as the voltage across C
increases, resulting in a progressively rising charging
function which accelerates the motor more and more with
increasing rotational speed. The charging function
determines the acceleration up to the set-point. The
charging current can have a maximum value of 55 mA.
Frequency-to-Voltage Converter
The
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 typ. –100 mV. The switch-off
threshold is given with –50 mV. The hysteresis
guarantees very reliable operation even when relatively
simple tacho generators are used. The tacho frequency is
given by:
where:
Rev. A4, 03-Aug-01
3
is first charged up to the starting voltage V
internal frequency-to-voltage converter (f/V-
t
t
t
t
t
V
V
f + n
V
1
2
1
3
tot
C3
12
0
+ t
t
2
1
60
= build-up of supply voltage
= charging of C
= dead time
= run-up time
= total start-up time to required speed
n = revolutions per minute
p = number of pulses per revolution
t
2
Figure 6. Soft start
p (Hz)
t
tot
3
2
t
). By then reducing the
to starting voltage
3
t
0
with a
3
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
amplified and then integrated by C
output on Pin 10. The conversion constant is determined
by C
the internally adjusted charge transfer gain.
G
k = G
The analog output voltage is given by
V
The values of C
possible input frequency, the maximum output voltage
V
on Pin 9 is approximately 6.7 kW. To obtain good
linearity of the f/V converter, the time constant resulting
from R
time span of the negative half-cycle for the highest
possible input frequency. The amount of remaining ripple
on the output voltage on Pin 10 is dependent on C
the internal charge amplification.
The ripple V
C
reduced.
The value of this capacitor should be chosen to fit the
particular control loop where it is going to be used.
Pulse Blocking
The output of pulses can be blocked by using Pin 18
(standby operation) and the system reset via the voltage
monitor if V
switching point hysteresis, the output is released when
V
turn-on.
Monitoring of the rotation can be carried out by
connecting an RC network to Pin 18. In the event of a
short or open circuit, the triac triggering pulses are cut off
by the time delay which is determined by R and C. The
capacitor C is discharged via an internal resistance
R
converter. If there are no more charge transfer processes,
C is charged up via R until the switch-off threshold is
exceeded and the triac triggering pulses are cut off. For
operation without trigger pulse blocking or monitoring of
the rotation, Pins 18 and 16 must be connected together.
6
i
i
O
O
V
18
. However, the increasing speed will then also be
= 2 kW with each charge transfer process of the f/V
I
does not exceed 6 V. While C
O
= k
I
10
5
9
, its charge transfer voltage of V
i
=
–1.5 V followed by a soft start such as that after
i
+ 8.3
and C
G
C
i
f
5
C
5
18
o
6
V
should be considerably less (1/5) than the
5
can be reduced by using larger values of
ch
R
and C
6
–1.25 V. After cycling through the
C
6
V
5
must be such that for the highest
ch
5
is charging up, the R
6
ch
U211B
at the converter
, R
5
6
is internally
(Pin 10) and
5
, C
5 (21)
6
and
i