AN6657, AN6657S
s
Supplementary Explanation
• Principle of Functioning
The AN6657 and the AN6657S are the electronic
governors which control the motor speed constantly by
making use of the fact that the counter electromotive force
generated in the motor winding is proportional to the motor
speed when the DC motor rotates. They have two motor drive
systems which correspond to the forward and reverse
rotations, respectively. The inter-pin voltage of the motor Em
is given by the following expression.
Em = Ea + Ra Ia
Ea : Motor reverse electromotive voltage
Ra : Motor internal resistor
(1)
ICs for Motor
speed signal. In Fig. 1, the motor speed N (∝ motor generated
voltage Ea) in the motor control state can be expressed by the
following formula.
r
5
r
2
+ r
3
r
1
r
2
Ea = V
REF
r
·
+
r
3
– Ra Ia
3
r
4
+ r
5
+ V
CE SAT1
(4)
The expression (4) applies in case of motor forward rotation,
in which a current flows from the motor + pin (5) to the
motor – pin (8). The following expression applies in case of
motor reverse rotation, in which a current flows form the
motor – pin (8) to the motor + pin (5).
Ea = V
REF
r
5
r
2
+ r
3
·
+
r
3
r
4
+ r
5
r
1
r
2
r
3
– Ra Ia
Ia : Motor current
There are the following relationships between the motor
reverse electromotive voltage Ea and Motor speed, and motor
torque T and motor current Ia, respectively.
Ea = Ka · N
T = K
T
· Ia
Ka : Motor generation constant
K
T
: Motor torque constant
In the expression (1), the inter-pin voltage of the motor Em
includes the voltage Ra · Ia which changes depending on
motor current Ia. The counter electromotive voltage Ea is
taken out by configuring the bridge circuit and used as a motor
(2)
(3)
(5)
V
REF
: Reference voltage, Ra : Motor internal resistor
Ia : Motor current
r
2
, r
3
: Diffusion resistance in the IC, r
4
, r
5
: Resistance for
speed control
r
1
: Torque control Resistance
V
CE
V
CE
SAT1
+V
CE SAT2
SAT2
: Forward/reverse drive circuit saturation voltage
when motor forward rotation is set
: Forward/reverse drive circuit saturation voltage
when motor reverce rotation is set
V
CC
+
Constant Speed/
Fast Forward
Forward/
Reverse
S/S
1
r
1
< 10 Ra
4.7µF
–
NC
16
15
14
13
12
11
10
9
Drive Mode
Switching Logic
Reference
Voltage
Forward/
Reverse
Drive Circuit
r
2
2SD2249
or
2SD2177
r
3
1kΩ
10kΩ
Amp.
1
15kΩ
1kB
r
5
680Ω
r
6
2
4.3kΩ
3
1
4
0.022µF
5
6
7
8
r
4
2SD2249
or
2SD2177
+
M
2
–
=
0.01µF
Ea
Ra
Ra : Motor-coiled resistor
Ea : Motor counter electromotive voltage
1
: Oscillation preventive capacitor
2
: Prevention of motor noise
Fig.1 AN6657/AN6657S Motor Control Basic Circuit
PANASONIC [ PANASONIC SEMICONDUCTOR ]
