FAN8902 Fairchild Semiconductor, FAN8902 Datasheet - Page 9

• Manufacturer Part Number: FAN8902
• Description: Motor / Motion / Ignition Controllers & Drivers Fan Motor Controller DC
• Manufacturer: Fairchild Semiconductor
• Type: Fan Motor Controllerr

Specifications of FAN8902

• Operating Current: 8mA
• Operating Temperature Classification: Industrial
• Package Type: PDIP
• Operating Supply Voltage (typ): 12V
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 32 V
• Supply Current: 8 mA
• Mounting Style: Through Hole
• Package / Case: DIP-14
• Operating Temperature: - 40 C to + 90 C
• Lead Free Status / RoHS Status: Compliant

FAN8902(KA3902)
In the steady state, the terminal voltage on a motor is consisted of a back EMF and the voltage drop on the armarture resistors.
When the motor happens to be stalled, the back EMF becomes zero, and the motor current (I
maximum values.
Therefore the duty of the pin #12 output becomes lower because of the increase of the sense voltage (V
voltage (V
This mechanism makes the motor current hold very low value in the stalled motor state.
The voltage on pin #14 (V
We can choose the ratio of the resistors, R2 and R3, as follows:
The buffer OP-amp selects the lower command between V
the above figure. Because of much larger V
toward B’ and then B” through the curve from the instance of stall as the below figure.
9
- Applied the rated voltage on motor, and then measured the current IRAT
- Matched the maximum command current, V
- V
V
La
V
for example, if R
Ratio = R3 / (R2 + R3) = V
Therefore, R2 : R3 = 8 : 5
CMD,MAX
La,MAX
=
La
V
BAT
) be lowered, then it makes the duty become lower again.
= 5V = V
V
D
= V
CMD,MAX
--------------------- -
R2
La,MAX
S
= 10m and I
R3
BAT
+
La
V
R3
MOTOR,STALL
) ia calculated as follows:
= V
= R
1 R3 / (R2 + R3)
V
CMD,MAX
MOTOR
La,MAX
V
S
BAT
Assumed the saturation voltage of Q1 is zero.
RAT
I
RAT
B”
V
LA
La
= 20[A] at V
= 10m
/ V
than V
V
5 5
B’
Operating curve
BAT
LA
CMD,MAX
= 5 / 13
CMD
20 25 = 5V
V
A
BAT
CMD
, the motor operating point stays at A. But the point gradually moves
CMD
= 13[V],
to I
V
B
LA
and V
RAT
.
La
I
RAT
so as to limit the stalled motor current to very low in
The voltage drop
on the amarture resistance
VLa curve
(1 / R)
M
) is quickly increased until a
RS
). Also it makes the