NJM3772 New Japan Radio, NJM3772 Datasheet - Page 7

• Manufacturer Part Number: NJM3772
• Description: DUAL STEPPER MOTOR DRIVER
• Manufacturer: New Japan Radio

External components
The NJM3772 exhibits substantially less power dissipation than most other comparable stepper motor driver ICs on
the market. This has been achieved by creating an external voltage drop in series with the upper transistor in the
output H-bridge, see figure 3. The voltage drop reduces the collector-emitter saturation voltage of the internal
transistor, which can greatly reduce power dissipation of the IC itself. The series resistor, designated R
selected for about 0.5 V voltage drop at the maximum output current. In an application with an output current of
1000 mA (peak), a 0.47 ohm,
1
omitted, and the V
connected externally to the circuit. These diodes shall be of fast type, with a t
are UF4001 or BYV27.
The recommended filter component values, 1 kohm and 820 pF, are suitable for a wide range of motors and
operational conditions.
the sensing resistor, and hence the peak motor current, will reach a slightly higher level than than what is defined
by the comparator threshold, V
performance. Increasing the time constant may result in unstable switching. The time constant should be adjusted
by changing the C
values result in a clock frequency (= switching frequency) of 26.5 kHz. A lower frequency will result in higher
current ripple, but may improve low-current level linearity. A higher clock frequency reduces current ripple, but
increases the switching losses in the IC and possibly the iron losses in the motor. If the clock frequency needs to
be changed, the C
current, reference voltage and the value of R
maximum output current which is
current, which is 1000 mA peak, when both channels is activated.
/2 W resistor is the best choice.
In low current applications where power dissipation is not a critical factor, the R
Contributing to the low power dissipation is the fact that the upper recirculation diodes in the output H- bridge are
A low pass filter in series with the comparator input prevents erroneous switching due to switching transients.
Since the low-pass filtering action introduces a small delay of the signal to the comparator, peak voltage across
The time constant of the low-pass filter may therefore be reduced to minimize the delay and optimize low-current
The frequency of the clock oscillator is set by the R
The sensing resistor R
C
MM
T
value.
capacitor value should be adjusted. The recommended R
and V
S
, should be selected for maximum motor current. The relationship between peak motor
BB
pins (pins 5, 11, 18, 27) can all be connected directly to the motor supply voltage V
CH
, set by the reference input V
1200 mA peak when only one channel is activated. Or recommended output
S
is described under Current control above. Be sure not to exceed the
T
-C
T
timing components at the RC pin. The recommended
R
(V
CH
= 450 mV at V
rr
T
of less than 100 ns. Common types
resistor value is 15 kohm.
B
R
resistor can of course be
= 2.5 V).
NJM3772
B
, shall be
MM
.