ATMEL U211B User Manual

Features

• Internal Frequency-to-voltage Converter

• Externally Controlled Integrated Amplifier

• Overload Limitation with “Fold Back” Characteristic

• Optimized Soft-start Function

• Tacho Monitoring for Shorted and Open Loop

• Automatic Retriggering Switchable

• Triggering Pulse Typically 155 mA

• Voltage and Current Synchronization

• Internal Supply-voltage Monitoring

• Temperature Reference Source

• Current Requirement ≤ 3 mA

1. Description

The integrated circuit U211B is designed as a phase-control circuit in bipolar technol­ogy with an internal frequency-to-voltage converter. The device includes an internal
control amplifier which means it can be used for speed-regulated motor applications.

Amongst others, the device features integrated load limitation, tacho monitoring and
soft-start functions, to realize sophisticated motor control systems.

Phase Control
IC with
Overload
Limitation
for Tacho
Applications

Figure 1-1. Block Diagram

1(1)

11(10)

10(9)

14(13)

15(14)

17(16)

Voltage/current

detector

Control
amplifier

+

-

Load limitation

speed/time

controlled

Controlled

current sink

5*

Automatic
retriggering

Phase-

control unit

ϕ = f (V12)

Soft start

-V

Ref

12(11) 13(12) 9(8)

Frequency-

to-voltage

converter

limitation

Reference

monitoring

Pulse-blocking

monitoring

8(7)

Output

pulse

Supply
voltage

voltage

Voltage

tacho

4(4)

6(5)

7(6)

3(3)

2(2)

16(15)

18*

-V
S

GND

U211B

Pin numbers in brackets refer to SO16

* Pins 5 and 18 connected internally

Rev. 4752B–INDCO–09/05

2. Pin Configuration

Figure 2-1. Pinning DIP18

I

sync

1

18

PB/TM

GND

Output

Retr

V

F/V

C

Table 2-1. Pin Description

Pin Symbol Function

1I

sync

2 GND Ground
3V

S

4 Output Trigger pulse output
5 Retr Retrigger programming
6V
7C

RP

P

8 F/V Frequency-to-voltage converter
9C

RV

10 OP- OP inverting input
11 OP+ OP non-inverting input
12 CTR/OPO Control input/OP output
13 C
14 I

soft

sense

15 OVL Overload adjust
16 V
17 V

Ref

sync

18 PB/TM Pulse blocking/tacho monitoring

Current synchronization

Supply voltage

Ramp current adjust
Ramp voltage

Charge pump

Soft start
Load-current sensing

Reference voltage
Voltage synchronization

2

V

3

S

4

5

6

RP

C

7

P

U211B

8

9

RV

V

17

V

16

OVL

15

I

14

C

13

CTR/OPO

12

OP+

11

OP-

10

sync

Ref

sense

soft

2

U211B

4752B–INDCO–09/05

Figure 2-2. Pinning SO16

I

sync

U211B

1

16

V

sync

GND

Output

Table 2-2. Pin Description

Pin Symbol Function

1I

sync

2 GND Ground
3V

S

4 Output Trigger pulse output
5V
6C

RP

P

7 F/V Frequency-to-voltage converter
8C

RV

9 OP- OP inverting input
10 OP+ OP non-inverting input
11 CTR/OPO Control input/OP output
12 C
13 I

soft

sense

14 OVL Overload adjust
15 V
16 V

Ref

sync

Current synchronization

Supply voltage

Ramp current adjust
Ramp voltage

Charge pump

Soft start
Load-current sensing

Reference voltage
Voltage synchronization

V

V

C

F/V

C

RP

RV

2

3

S

4

15

14

13

V

Ref

OVL

I

sense

U211B

5

6

P

7

8

12

11

10

9

C

soft

CTR/OPO

OP+

OP-

4752B–INDCO–09/05

3

3. Mains Supply

The U211B is equipped with voltage limiting and can therefore be supplied directly from the
mains. The supply voltage between pin 2 (+ pol/_|_) and pin 3 builds up across D
smoothed by C

VMVS–

---------------------=

R

1

2 I

. The value of the series resistance can be approximated using:

1

S

and R1 and is

1

Further information regarding the design of the mains supply can be found in the section “Design

Hints” on page 9. The reference voltage source on pin 16 of typically -8.9 V is derived from the

supply voltage and is used for regulation.

Operation using an externally stabilized DC voltage is not recommended.

4. Phase Control

If the supply cannot be taken directly from the mains because the power dissipation in R

would

1

be too large, the circuit as shown in Figure 3-1 should be used.

Figure 3-1. Supply Voltage for High Current Requirements

~

24 V~

123

C

R

1

1

4

5

The phase angle of the trigger pulse is derived by comparing the ramp voltage (which is mains
synchronized by the voltage detector) with the set value on the control input pin 12. The slope of
the ramp is determined by C
R

on pin 6. The maximum phase angle α

2

and its charging current. The charging current can be varied using

2

can also be adjusted by using R

max

.

2

When the potential on pin 7 reaches the nominal value predetermined at pin 12, a trigger pulse
is generated whose width t

is determined by the value of C2 (the value of C2 and hence the

p

pulse width can be evaluated by assuming 8 µs/nF). At the same time, a latch is set, so that as
long as the automatic retriggering has not been activated, no more pulses can be generated in
that half cycle.

The current sensor on pin 1 ensures that, for operations with inductive loads, no pulse will be
generated in a new half cycle as long as a current from the previous half cycle is still flowing in
the opposite direction to the supply voltage at that instant. This makes sure that “gaps” in the
load current are prevented.

The control signal on pin 12 can be in the range of 0 V to -7 V (reference point pin 2).

If V

= -7 V, the phase angle is at maximum (α

12

The phase angle is minimum (

4

U211B

α

min

) when V

12

), i.e., the current flow angle, is at minimum.

max

= V2.

4752B–INDCO–09/05

5. Voltage Monitoring

As the voltage is built up, uncontrolled output pulses are avoided by internal voltage surveil­lance. At the same time, all latches in the circuit (phase control, load limit regulation, soft start)
are reset and the soft-start capacitor is short circuited. Used with a switching hysteresis of
300 mV, this system guarantees defined start-up behavior each time the supply voltage is
switched on or after short interruptions of the mains supply.

6. Soft Start

As soon as the supply voltage builds up (t1), the integrated soft start is initiated. Figure 6-1
shows the behavior of the voltage across the soft-start capacitor, which is identical with the volt­age on the phase-control input on pin 12. This behavior guarantees a gentle start-up for the
motor and automatically ensures the optimum run-up time.

Figure 6-1. Soft Start

U211B

V

C3

V

12

V

0

t

1

t

2

t

3

t

tot

t

t1 = Build-up of supply voltage
t

= Charging of C3 to starting voltage

2

+ t2 = Dead time

t

1

= Run-up time

t

3

= Total start-up time to required speed

t

tot

C

is first charged up to the starting voltage V0 with a current of typically 45 µA (t2). By reducing

3

the charging current to approximately 4 µA, the slope of the charging function is also 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

3

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 µA.

4752B–INDCO–09/05

5

7. Frequency-to-voltage Converter

∆

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 sim­ple tacho generators are used.

The tacho frequency is given by:

n

------

f

where: n = Revolutions per minute

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

6

transfer voltage of V

G

i

p (Hz)×=

60

p = Number of pulses per revolution

at the converter output on pin 10. The conversion constant is determined by C5, its charge

, R6 (pin 10) and the internally adjusted charge transfer gain.

ch

I

10

-------

I

8.3=

9

is internally amplified and then integrated by

5

k = G

× C5 × R6 × V

i

ch

The analog output voltage is given by

V

= k × f

O

The values of C
mum output voltage V

and C6 must be such that for the highest possible input frequency, the maxi-

5

does not exceed 6 V. While C5 is charging up, the Ri on pin 9 is

O

approximately 6.7 kΩ. To obtain good linearity of the f/V converter, the time constant resulting
from R

and C5 should be considerably less (1/5) than the time span of the negative half-cycle for

i

the highest possible input frequency. The amount of remaining ripple on the output voltage on
pin 10 is dependent on C

GiVch× C5×

V

-------------------------------------=

O

The ripple ∆V

C

6

can be reduced by using larger values of C6. However, the increasing speed will

O

, C6 and the internal charge amplification.

5

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.

6

U211B

4752B–INDCO–09/05

7.1 Pulse Blocking

U211B

The output of pulses can be blocked by using pin 18 (standby operation) and the system reset
via the voltage monitor if V
output is released when V

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
charge transfer process of the f/V 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, pin 18 and pin 16
must be connected together.

Figure 7-1. Operation Delay

≥ -1.25 V. After cycling through the switching point hysteresis, the

18

≤ -1.5 V, followed by a soft start such as after turn-on.

18

= 2 kΩ with each

i

C = 1 µF

10 V

7.2 Control Amplifier

The integrated control amplifier (see Figure 10-17 on page 21) with differential input compares
the set value (pin 11) with the instantaneous value on pin 10, and generates a regulating voltage
on the output pin 12 (together with the external circuitry on pin 12). This pin always tries to keep
the actual voltage at the value of the set voltages. The amplifier has a transmittance of typically
1000 µA/V and a bipolar current source output on pin 12 which operates with typically ±110 µA.
The amplification and frequency response are determined by R
out). For open-loop operation, C
connected with pin 12 and pin 8 with pin 2. The phase angle of the triggering pulse can be
adjusted by using the voltage on pin 11. An internal limitation circuit prevents the voltage on
pin 12 from becoming more negative than V

R = 1 MΩ

18

, C5, R6, R7, C7, C8 and R11 can be omitted. Pin 10 should be

4

17 16 15

123

+ 1 V.

16

4

, C7, C8 and R11 (can be left

7

7.3 Load Limitation

The load limitation, with standard circuitry, provides full protection against overloading of the
motor. The function of load limiting takes account of the fact that motors operating at higher
speeds can safely withstand larger power dissipations than at lower speeds due to the increased
action of the cooling fan. Similarly, considerations have been made for short-term overloads for
the motor which are, in practice, often required. These behaviors are not damaging and can be
tolerated.

4752B–INDCO–09/05

7

In each positive half-cycle, the circuit measures, via R10, the load current on pin 14 as a potential
drop across R
available on pin 15 and is integrated by C
angle for current flow, the voltage on C

and produces a current proportional to the voltage on pin 14. This current is

8

. If, following high-current amplitudes or a large phase

9

exceeds an internally set threshold of approximately

9

7.3 V (reference voltage pin 16), a latch is set and load limiting is turned on. A current source
(sink) controlled by the control voltage on pin 15 now draws current from pin 12 and lowers the
control voltage on pin 12 so that the phase angle α is increased to α

max

.

The simultaneous reduction of the phase angle during which current flows causes firstly a reduc­tion of the rotational speed of the motor which can even drop to zero if the angular momentum of
the motor is excessively large, and secondly a reduction of the potential on C

which in turn

9

reduces the influence of the current sink on pin 12. The control voltage can then increase again
and bring down the phase angle. This cycle of action sets up a “balanced condition” between the
“current integral” on pin 15 and the control voltage on pin 12.

Apart from the amplitude of the load current and the time during which current flows, the poten­tial on pin 12 and hence the rotational speed also affects the function of load limiting. A current
proportional to the potential on pin 10 gives rise to a voltage drop across R
the current measured on pin 14 is smaller than the actual current through R

, via pin 14, so that

10

.

8

This means that higher rotational speeds and higher current amplitudes lead to the same current
integral. Therefore, at higher speeds, the power dissipation must be greater than that at lower
speeds before the internal threshold voltage on pin 15 is exceeded. The effect of speed on the
maximum power is determined by the resistor R

and can therefore be adjusted to suit each

10

individual application.

If, after load limiting has been turned on, the momentum of the load sinks below the “o-momen­tum” set using R

, V15 will be reduced. V12 can then increase again so that the phase angle is

10

reduced. A smaller phase angel corresponds to a larger momentum of the motor and hence the
motor runs up, as long as this is allowed by the load momentum. For an already rotating
machine, the effect of rotation on the measured “current integral” ensures that the power dissi­pation is able to increase with the rotational speed. The result is a current-controlled
acceleration run-up which ends in a small peak of acceleration when the set point is reached.
The load limiting latch is simultaneously reset. Then the speed of the motor is under control
again and is capable of carrying its full load. The above mentioned peak of acceleration depends
upon the ripple of actual speed voltage. A large amount of ripple also leads to a large peak of
acceleration.

The measuring resistor R

should have a value which ensures that the amplitude of the voltage

8

across it does not exceed 600 mV.

8

U211B

4752B–INDCO–09/05

7.4 Design Hints

U211B

Practical trials are normally needed for the exact determination of the values of the relevant
components for load limiting. To make this evaluation easier, the following table shows the effect
of the circuitry on the important parameters for load limiting and summarizes the general
tendencies.

Table 7-1. Load Limiting Parameters

Component Component Component

Parameters

P

max

P

min

P

max/min

t

d

t

r

P

max

P

min

t

d

t

r

- Maximum continuous power dissipationP1 = f

- Power dissipation with no rotation P1 = f

- Operation delay time

- Recovery time

n.e. - No effect

R10 Increasing R9 Increasing C9 Increasing

Increases Decreases n.e.
Increases Decreases n.e.
Increases n.e. n.e.
n.e. Increases Increases
n.e. Increases Increases

n ≠ 0

(n)

n = 0

(n)

7.5 Pulse-output Stage

The pulse-output stage is short-circuit protected and can typically deliver currents of 125 mA.
For the design of smaller triggering currents, the function I

10-12 on page 18.

7.6 Automatic Retriggering

The variable automatic retriggering prevents half cycles without current flow, even if the triac has
been turned off earlier, e.g., due to a collector which is not exactly centered (brush lifter) or in the
event of unsuccessful triggering. If necessary, another triggering pulse is generated after a time
lapse which is determined by the repetition rate set by resistance between pin 5 and pin 3 (R
With the maximum repetition rate (pin 5 directly connected to pin 3), the next attempt to trigger
comes after a pause of 4.5 t
ishes. If pin 5 is not connected, only one trigger pulse per half cycle is generated. Since the
value of R
for a fixed value of C

= f(RGT) can be taken from Figure

GT

and this is repeated until either the triac fires or the half cycle fin-

p

determines the charging current of C2, any repetition rate set using R

5-3

.

2

is only valid

5-3

5-3

).

4752B–INDCO–09/05

9