NJM37770D9 New Japan Radio Co., Ltd., NJM37770D9 Datasheet - Page 4

• Manufacturer Part Number: NJM37770D9
• Description: Motion Motor Control, 5V Operating Voltage, -40C to 150C Operating Temperature, DIP
• Manufacturer: New Japan Radio Co., Ltd.

Current level selection.
The status of I
selected according to the table below.
value of the sensing resistor R
i
Current sensor
The current sensor contains a reference voltage divider and three comparators for measuring each of the selectable
current levels. The motor current is sensed as a voltage drop across the current sensing resistor, R
with one of the voltage references from the divider. When the two voltages are equal, the comparator triggers the
single-pulse generator. Only one comparator at a time is activated by the input logic.
Single-pulse generator
The pulse generator is a monostable multivibrator triggered on the positive edge of the comparator output. The
multivibrator output is high during the pulse time, t
t
Output stage
The output stage contains four transistors and two diodes, connected in an H-bridge. Note that the upper recircula-
tion diodes are connected to the circuit externally. The two sinking transistors are used to switch the power supplied
to the motor winding, thus driving a constant current through the winding. See figures 3 and 4.
Overload protection
The circuit is equipped with a thermal shut-down function, which will limit the junction temperature. The output current
will be reduced if the maximum permissible junction temperature is exceeded. It should be noted, however, that it is
not short circuit protected.
Operation
When a voltage V
i
R = Winding resistance
L = Winding inductance
t = time
(see figure 3, arrow 1)
through a low-pass filter, R
above the comparator threshold voltage, the monostable is triggered and its output turns off the conducting sink
transistor.The polarity across the motor winding reverses and the current is forced to circulate through the appropri-
ate upper protection diode back through the source transistor (see figure 3, arrow 2).
below the comparator threshold level.The sinking transistor then turns on and the motor current starts to increase
again, The cycle is repeated until the current is turned off via the logic inputs.When both I
transistors in the output H-bridge are turned off, which means that inductive current recirculates through two opposite
free-wheeling diodes (see figure 3, arrow 3). this method of turning off the current results in a faster current decay
than if only one transistor was turned off and will therefore improve speed performance in half-stepping mode.
m
m
Motor current
High level
Medium level 60%
Low level
Zero current
off
The specific values of the different current levels are determined by the reference voltage V
The peak motor current can be calculated as follows:
The motor current can also be continuously varied by modulating the voltage reference input.
The single pulse switches off the power feed to the motor winding, causing the winding to decrease during t
If a new trigger signal should occur during t
The motor current appears across the external sensing resistor, R
After the monostable has timed out, the current has decayed and the analog voltage across the sensing resistor is
= (V
= (V
= 0.69 • R
R
MM
• 0.080) / R
/ R) • (1 - e
T
• C
0
100%
and I
20%
0%
T
MM
S
-(R • t ) / L
1
is applied across the motor winding, the current rise follows the equation:
[A], at 100% level
inputs determines the current level in the motor winding. Three fixed current levels can be
I
L
H L
L
H H
0
)
C
C
I
L
H
1
C
S
, to the voltage comparator input (pin 10). At the moment the sensed voltage rises
.
off
, it is ignored.
off
, which is determined by the timing components R
S
, as an analog voltage. This voltage is fed
1
and I
R
NJM37770
together with the
0
are high, all four
S
, and compared
T
and C
T
off
.
.