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부품번호 3955 기능
기능 FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER
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3955 데이터시트, 핀배열, 회로
3955
PFD 1
REF 2
VBB
RC 3
GROUND 4
GROUND 5
LOGIC
SUPPLY
6 VCC
PHASE 7
LOGIC
D2 8
16
LOAD
SUPPLY
15 OUTB
14 D 0
13 GROUND
12 GROUND
11 SENSE
10 OUTA
9 D1
Dwg. PP-056-2
Note the A3955SB (DIP) and the A3955SLB
(SOIC) are electrically identical and share a
common terminal number assignment.
ABSOLUTE MAXIMUM RATINGS
Load Supply Voltage, VBB . . . . . . . . . . 50 V
Output Current, IOUT
(Continuous) . . . . . . . . . . . . . . ±1.5 A*
Logic Supply Voltage, VCC . . . . . . . . . 7.0 V
Logic/Reference Input Voltage Range,
VIN . . . . . . . . . . . -0.3 V to VCC + 0.3 V
Sense Voltage, VS . . . . . . . . . . . . . . . . 1.0 V
Package Power Dissipation,
PD . . . . . . . . . . . . . . . . . . . . See Graph
Operating Temperature Range,
TA . . . . . . . . . . . . . . . . . -20˚C to +85˚C
Junction Temperature, TJ . . . . . . . +150˚C†
Storage Temperature Range,
TS . . . . . . . . . . . . . . . . -55˚C to +150˚C
* Output current rating may be limited by duty
cycle, ambient temperature, and heat sinking.
Under any set of conditions, do not exceed the
specified current rating or a junction temperature
of 150˚C.
† Fault conditions that produce excessive junction
temperature will activate the device’s thermal
shutdown circuitry. These conditions can be
tolerated but should be avoided.
FULL-BRIDGE PWM
MICROSTEPPING MOTOR DRIVER
The A3955SB and A3955SLB are designed for driving one winding
of a bipolar stepper motor in a microstepping mode. The outputs are
rated for continuous output currents to ±1.5 A and operating voltages
to 50 V. Internal pulse-width modulated (PWM) current control com-
bined with an internal three-bit nonlinear digital-to-analog converter
allows the motor current to be controlled in full-, half-, quarter-, or
eighth-step (microstepping) modes. Nonlinear increments minimize
the number of control lines necessary for microstepping.
Microstepping provides for increased step resolution, and reduces
torque variations and resonance problems at low speed.
Internal circuitry determines whether the PWM current-control
circuitry operates in a slow (recirculating) current-decay mode, fast
(regenerative) current-decay mode, or in a mixed current-decay mode
in which the off time is divided into a period of fast current decay with
the remainder of the fixed off time spent in slow current decay. The
combination of user-selectable current-sensing resistor and reference
voltage, digitally selected output current ratio; and slow, fast, or mixed
current-decay modes provides users with a broad, variable range of
motor control.
Internal circuit protection includes thermal shutdown with hyster-
esis, transient-suppression diodes, and crossover current protection.
Special power-up sequencing is not required.
The A3955S— is supplied in a choice of two power packages; a
16-pin dual-in-line plastic package with copper heat-sink tabs (suffix
‘B’), and a 16-lead plastic SOIC with copper heat-sink tabs (suffix ‘LB’).
For both package styles, the power tab is at ground potential and
needs no electrical isolation.
FEATURES
s ±1.5 A Continuous Output Current
s 50 V Output Voltage Rating
s Internal PWM Current Control
s 3-Bit Non-Linear DAC
s Fast, Mixed Fast/Slow, and Slow Current-Decay Modes
s Internal Transient-Suppression Diodes
s Internal Thermal-Shutdown Circuitry
s Crossover-Current and UVLO Protection
Always order by complete part number:
Part Number
Package
A3955SB
16-Pin DIP
A3955SLB
16-Lead SOIC




3955 pdf, 반도체, 판매, 대치품
3955
FULL-BRIDGE PWM
MICROSTEPPING
MOTOR DRIVER
ELECTRICAL CHARACTERISTICS at TA = 25˚C, VBB = 5 V to 50 V, VCC = 4.5 V to 5.5 V
(unless otherwise noted. )
Limits
Characteristic
Symbol Test Conditions
Min.
Typ. Max. Units
Control Circuitry
Logic Supply Voltage Range
Reference Voltage Range
UVLO Enable Threshold
UVLO Hysteresis
Logic Supply Current
Logic Input Voltage
Logic Input Current
Mixed-Decay Comparator
Trip Points
Mixed-Decay Comparator
Input Offset Voltage
Mixed-Decay Comparator
Hysteresis
Reference Input Current
Reference Divider Ratio
Digital-to-Analog Converter
Accuracy*
Current-Sense Comparator
Input Offset Voltage*
VCC
VREF
Operating
Operating
VCC = 0 ¡ 5 V
ICC(ON)
ICC(OFF)
VIN(1)
VIN(0)
IIN(1)
IIN(0)
VPFD
VIO(PFD)
D0 = D1 = D2 = 0.8 V
VIN = 2.0 V
VIN = 0.8 V
Slow Current-Decay Mode
Mixed Current-Decay Mode
Fast Current-Decay Mode
VIO(PFD)
IREF
VREF/VS
VIO(S)
VREF = 0 V to 2.5 V
at trip, D0 = D1 = D2 = 2 V
1.0 V < VREF 2.5 V
0.5 V < VREF 1.0 V
VREF = 0 V
4.5 5.0 5.5
0.5 — 2.5
3.35 3.70 4.05
0.30 0.45 0.60
— 42 50
— 12 16
2.0 —
— — 0.8
— <1.0 20
— <-2.0 -200
3.5 —
1.1 — 3.1
— — 0.8
— 0 ±20
5.0 25 55
— — ±5.0
— 3.0 —
— — ±3.0
— — ±4.0
— — ±5.0
V
V
V
V
mA
mA
V
V
µA
µA
V
V
V
mV
mV
µA
%
%
mV
Step Reference
Current Ratio
SRCR
D0 = D1 = D2 = 0.8 V
D0 = 2 V, D1 = D2 = 0.8 V
D0 = 0.8 V, D1 = 2 V, D2 = 0.8 V
D0 = D1 = 2 V, D2 = 0.8 V
D0 = D1 = 0.8 V, D2 = 2 V
D0 = 2 V, D1 = 0.8 V, D2 = 2 V
D0 = 0.8 V, D1 = D2 = 2 V
D0 = D1 = D2 = 2 V
—0—
— 19.5 —
— 38.2 —
— 55.5 —
— 70.7 —
— 83.1 —
— 92.4 —
— 100 —
%
%
%
%
%
%
%
%
Continued next page…
* The total error for the VREF/VS function is the sum of the D/A error and the current-sense comparator input offset voltage.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

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3955 전자부품, 판매, 대치품
3955
FULL-BRIDGE PWM
MICROSTEPPING
MOTOR DRIVER
Functional Description
Two A3955S— full-bridge PWM microstepping motor
drivers are needed to drive the windings of a bipolar
stepper motor. Internal pulse-width modulated (PWM)
control circuitry regulates each motor winding’s current.
The peak motor current is set by the value of an external
current-sense resistor (RS), a reference voltage (VREF),
and the digital-to-analog converter (DAC) data inputs (D0,
D1, and D2).
To improve motor performance, especially when using
sinusoidal current profiles necessary for microstepping,
the A3955S— has three distinct current-decay modes:
slow decay, fast decay, and mixed decay.
PHASE Input. The PHASE input controls the direction of
current flow in the load (table 1). An internally generated
dead time of approximately 1 µs prevents crossover
currents that could occur when switching the PHASE
input.
DAC Data Inputs (D0, D1, D2). A non-linear DAC is used
to digitally control the output current. The output of the
DAC is used to set the trip point of the current-sense
comparator. Table 3 shows DAC output voltages for each
input condition. When D0, D1, and D2 are all logic low, all
of the power output transistors are turned off.
Internal PWM Current Control. Each motor driver
contains an internal fixed off-time PWM current-control
circuit that limits the load current to a desired value (ITRIP).
Initially, a diagonal pair of source and sink transistors are
enabled and current flows through the motor winding and
V
BB
DRIVE CURRENT
RECIRCULATION
(SLOW-DECAY MODE)
RECIRCULATION
(FAST-DECAY MODE)
RS
Dwg. EP-006-15
Figure 1 — Load-Current Paths
RS (figure 1). When the voltage across the sense resistor
equals the DAC output voltage the current-sense com-
parator resets the PWM latch, which turns off the source
drivers (slow-decay mode) or the sink and source drivers
(fast- or mixed-decay mode).
With the DATA input lines tied to VCC, the maximum
value of current limiting is set by the selection of RS and
VREF with a transconductance function approximated by:
ITRIP VREF/3RS.
The actual peak load current (IPEAK) will be slightly higher
than ITRIP due to internal logic and switching delays. The
driver(s) remain off for a time period determined by a
user-selected external resistor-capacitor combination
(RTCT). At the end of the fixed off time, the driver(s) are
re-enabled, allowing the load current to increase to ITRIP
again, maintaining an average load current.
The DAC data input lines are used to provide up to
eight levels of output current. The internal 3-bit digital-to-
analog converter reduces the reference input to the
current-sense comparator in precise steps (the step
reference current ratio or SRCR) to provide half-step,
quarter-step, or “microstepping” load-current levels.
ITRIP SRCR x VREF/3RS
Slow Current-Decay Mode. When VPFD 3.5 V, the
device is in slow current-decay mode (the source drivers
are disabled when the load current reaches ITRIP). During
the fixed off time, the load inductance causes the current
to recirculate through the motor winding, sink driver,
ground clamp diode, and sense resistor (see figure 1).
Slow-decay mode produces low ripple current for a given
fixed off time (see figure 2). Low ripple current is desir-
able because the average current in the motor winding is
more nearly equal to the desired reference value, result-
ing in increased motor performance in microstepping
applications.
For a given level of ripple current, slow decay affords
the lowest PWM frequency, which reduces heating in the
motor and driver IC due to a corresponding decrease in
hysteretic core losses and switching losses respectively.
Slow decay also has the advantage that the PWM load
current regulation can follow a more rapidly increasing
reference before the PWM frequency drops into the
audible range. For these reasons slow-decay mode is
typically used as long as good current regulation can be
maintained.

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