AN6657, AN6657S
• Current Limiting Function
ICs for Motor
The current limitting function detects the voltage drop of
All Temperatures
N (R.P.M.)
the torque control resistance r
1
, operates the PNP transistor,
and controls the input voltage of the amplifier in the IC to
limit the current.
Limiting the current can reduce the useless current at start
and motor lock time and prevent the supply voltage from
dropping.
The limited current I
Lim
is calculated by the following
expression.
I
Lim
=
V
Lim
r
1
(8)
T
M
(Torque)
Fig. 3.
r
1
Temperature Characteristics = Ra Tempera-
ture Characteristics
• Temperature Compensation of Motor Speed
For the normally used motor with core, the temperature
compensation of the motor speed can be done by using 3,900
r.p.m/˚C metal coated or coiled resistor as the torque control
resistance r
1
, and metal coated resistor with a positive
temperature coefficient of about 2,000r.p.m/˚C as the speed
control resistance r
4
.
V
Lim
: V
BEON
Voltage < 0.6V
When r
1
= 1.2Ω, from the expression (8) I
Lim
is ;
0.6V
I
Lim
=
= 500mA
1.2Ω
s
Characteristics Curve
P
D
– Ta
800
FF/REW
r.p.m. Load Torque
4000
Power Dissipation P
D
(mW)
600
R.p.m. N (rpm)
AN6657
400
Constant
Speed
2000
V
CC
= 9V
V
CC
= 6V
AN6657S
200
0
0
40
80
120
160
0
0
40
80
Load Torque T (g – cm)
120
160
Ambient Temperature Ta (˚C)
PANASONIC [ PANASONIC SEMICONDUCTOR ]
