NJM3777 New Japan Radio, NJM3777 Datasheet - Page 3

• Manufacturer Part Number: NJM3777
• Description: DUAL STEPPER MOTOR DRIVER
• Manufacturer: New Japan Radio

Each channel of the NJM3777 consists of the following sections: an output H-bridge with four transistors and four
recirculation diodes, capable of driving up to 800 mA continuous current to the motor winding, a logic section that
controls the output transistors, an S-R flip-flop, and a comparator. The clock-oscillator is common to both channels.
peak current through the winding via a current-sensing resistor R
winding. As the current increases, a voltage develops across the sensing resistor, which is fed back to the com-
parator. At the predetermined level, defined by the voltage at the reference input V
flop, which turns off the upper output transistor. The turn-off of one channel is independent of the other channel.
The current decreases until the clock oscillator triggers the flip-flops of both channels simultaneously, which turns
on the output transistors again, and the cycle is repeated.
clock oscillator provides a blanking pulse which is used for digital filtering of the voltage transient across the
current sensing resistor during turn-on.
Constant current control is achieved by switching the output current to the windings. This is done by sensing the
To prevent erroneous switching due to switching transients at turn-on, the NJM3777 includes a digital filter. The
The current paths during turn-on, turn-off and phase shift are shown in figure 3.
FUNCTIONAL DESCRIPTION
Figure 3. Output stage with current paths
during turn-on, turn-off and phase shift.
Motor Current
3
1
Fast Current Decay
Slow Current Decay
1
2
2
V
R
MM
S
S
, effectively connected in series with the motor
3
Time
R
, the comparator resets the flip-
NJM3777