ICs for Motor
As it is clear from the expression (4), r
1
r
2
/r
3
– Ra = 0, that is,
when r
1
= r
3
/r
2
÷Ra
is established, Ea (∝ motor speed N)
becomes a constant value without depending on the motor
current Ia (load torque T). This is also true for the expression
(5).
AN6657, AN6657S
• Setting the External Resistor r
1
The torque control resistance r
1
is important in setting the
motor rotating state. Select the resistance which satisfies the
condition of the expression (7) within a working temperature
range. If this condition is not satisfied, the motor may have
abnormal rotation such as hunting, etc.
r
3
r
1
<
r
2
Ra
≈
(r
3
/r
2
= 1/10 for the AN6657, AN6657S)
(7)
Ra is the copper coiled resistor of the motor and has the
temperature characteristics of + 3,900r.p.m/˚C, Therefore, it
is necessary to set the value of r
1
so that the relationship in
the expression (7) will be satisfied at the minimum working
temperature. The diffusion resistance r
3
/r
2
in the IC has the
flat temperature characteristics, and if the temperature
characteristics of r
1
is adjusted to that of Ra, + 3900 r.p.m/˚C,
the value of the second term (r
1
r
2
r – Ra) of the expressions
(4) and (5) shows the flat temperature characteristics and the
torque characteristics of the motor speed becomes constant
without depending on a temperature. Fig. 2 and Fig. 3 show
this relationship.
• Switching the Various Modes
The AN6657 and the AN6657S have five motor drive
modes as shown in Table 1. Those modes can be selected
depending on the voltage H (3V to 6V) and voltage L (0V to
0.7V) signals applied to the input pins14, 15 and 16.
1) Forward/reverse switching : Forward/reverse rotation is
switched over whether a current flows from the pin5 to
the pin8 (forward rotation) or vice versa (reverse
rotation).
2) Power-off (pause) mode : turning off the constant current
source inside the IC stops a current to the motor and stops
motor. In this mode, all the transistors of the IC are turned
off and only a leak current (20µA) is available.
3) Setting the motor speed
The motor speed at constant speed time can be expressed
by the expression (4).
V
REF
r
2
+r
3
r
3
·
r
5
r
4
· r
6
r
r
4
+r
6
+
5
Low Temperature
Normal Temperature
N (R.P.M.)
High Temperature
In the FF (REW) mode, the pin2 is turned on and the first
term of the expression (4) is ;
Ea =V
REF
r
2
+r
3
r
3
r
5
+
· r
4
· r
6
+ r
5
r
4
+r
6
r
1
r
2
r
3
– Ra Ia
T
M
(Torque)
+ V
CE SAT
(6)
and the motor speed N (motor generated voltage Ea) is
expressed as follows.
From the expression (4), the motor speed at constant speed
can be controlled with r
4
and r
5
(external VRs).
From the expression (6), the motor speed at the FF (REW)
mode can be controlled with r
6
.
Fig. 2
r
1
Temperature Characteristics < Ra Tempera-
ture Characteristics
Table 1 AN6657/AN6657S Mode Switching Table
Input
Pin14
L
H
H
H
H
Pin15
—
H
L
H
L
Pin16
—
L
L
H
H
Pin5 Motor +
—
H
L
H
L
Output
Pin8 Motor –
—
L
H
L
H
Pin2
OFF
OFF
OFF
ON
ON
Motor Drive Mode
Power OFF (pause)
Forward (constant speed)
Reverse (constant speed)
FF
REW
PANASONIC [ PANASONIC SEMICONDUCTOR ]
