Datasheet A3957SLB, A3957SA Datasheet (Allegro)

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Page 1

3957

FULL-BRIDGE PWM

MICROSTEPPING MOTOR DRIVER

Data Sheet

29319.44†

A3957SLB

CONNECT

GROUND

LOGIC

SUPPLY

PHASE

CONNECT

NC NC

PFD

REF

LOGIC

10 15

ABSOLUTE MAXIMUM RATINGS

Load Supply Voltage, VBB. . . . . . . . . 50 V

Output Current, I

(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 (TA = 25°C), P

A3957SA . . . . . . . . . . . . . . . . 2.08 W†

A3957SLB. . . . . . . . . . . . . . . 2.23 W†

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.

† Per SEMI G42-88 Specification, Thermal Test

Board Standardization for Measuring Junctionto-Ambient Thermal Resistance of Semiconductor Packages..

OUT

CONNECT LOAD

SUPPLY

OUT

CONNECT

GROUND

SENSE NO

CONNECT OUT

CONNECT

Dwg. PP-056-4

The A3957SA and A3957SLB 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 combined with an internal four-bit nonlinear digital-to-analog converter allows the motor current to be controlled in full-, half-, quarter-, eighth-, or sixteenth-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 hysteresis, transient-suppression diodes, and crossover current protection. Special power-up sequencing is not required.

The A3957S— is supplied in a choice of two power packages; a 16-pin dual-in-line plastic package (suffix ‘A’), and a 24-lead plastic SOIC with copper heat-sink tabs (suffix ‘LB’). The power tab is at ground potential and needs no electrical isolation.

FEATURES

■ ±1.5 A Continuous Output Current

■ 50 V Output Voltage Rating

■ Internal PWM Current Control

■ 4-Bit Non-Linear DAC for 16-Bit Microstepping

■ Satlington™ Sink Drivers

■ Fast, Mixed Fast/Slow, and Slow Current-Decay Modes

■ Internal Transient-Suppression Diodes

■ Internal Thermal-Shutdown Circuitry

■ Crossover-Current and UVLO Protection

Always order by complete part number:

Part Number Package R

θJA

A3957SA 16-pin DIP 60°C/W 38°C/W —

A3957SLB 24-lead batwing SOIC 56°C/W — 6°C/W

θJC

θJT

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3957

31120

171819

FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

FUNCTIONAL BLOCK DIAGRAM (A3957SLB shown)

PHASE

GROUND

PFD

UVLO & TSD

MIXED-DECAY

COMPARATOR

+ –

BLANKING

PWM LATCH

LOGIC

SUPPLY

BLANKING

GATE

+ –

OUT

CURRENT-SENSE

COMPARATOR

÷3

REF

+ –

D/A

OUT

LOAD

SUPPLY

SENSE

DISABLE

Dwg. FP-042-1

GROUND

OUT

LOAD

SUPPLY

PFD

REF

GROUND

A3957SA

LOGIC

CONNECT SENSE

OUT

PHASE LOGIC

SUPPLY

Dwg. PP-056-3

For the ‘A’ package, pins 1 and 8 must

be externally connected together.

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

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Table 1 — PHASE Truth Table

PHASE OUT

HH L

LL H

OUT

Table 2 — PFD Truth Table

PFD

≥3.5 V Slow Current-Decay Mode

1.2 V to 2.9 V Mixed Current-Decay Mode

≤0.8 V Fast Current-Decay Mode

Description

Table 3 — DAC Truth Table

DAC Data Current

HHHH 100 3.00

H H H L 95.7 3.13

H H L H 91.3 3.29

H H L L 87.0 3.45

H L H H 82.6 3.64

H L H L 78.3 3.83

H L L H 73.9 4.07

H L L L 69.6 4.31

L H H H 60.9 4.93

L H H L 52.2 5.74

L H L H 43.5 6.90

L H L L 34.8 8.62

L L H H 26.1 11.49

L L H L 17.4 17.24

Ratio, % V

REF/VS

L L L X All Outputs Disabled

where VS = I

• RS. See Applications section.

TRIP

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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

Power Outputs

Load Supply Voltage Range V

Output Leakage Current I

Output Saturation Voltage V (Forward or Reverse Mode)

CE(SAT)

Sense Current Offset I

CEX

Operating, I

= V

OUT

= 0 V — <-1.0 -50 µA

OUT

= ±1.5 A, L = 3 mH V

OUT

—50 V

— <1.0 50 µA

VS = 1.0 V:

Source Driver, I Source Driver, I Sink Driver, I Sink Driver, I

IS - I

OUT

, I

OUT

= 850 mA, 20 30 40 mA

= -0.85 A — 1.1 1.2 V

OUT

= -1.5 A — 1.4 1.5 V

OUT

= 0.85 A — 0.5 0.7 V

OUT

= 1.5 A — 1.2 1.5 V

OUT

VS = 0 V, VCC = 5 V

Clamp Diode Forward Volt. V (Sink or Source)

Motor Supply Current I (No Load)

BB(ON)

BB(OFF)

IF = 0.85 A — 1.2 1.4 V

IF = 1.5 A — 1.5 1.7 V

— 2.0 4.0 mA

D0 = D1 = D2 = D

= 0.8 V — 1.0 50 µA

Control Circuitry

Logic Supply Voltage Range V

Reference Voltage Range V

REF

UVLO Enable Threshold V

Operating 4.5 5.0 5.5 V

Operating 0.5 — 2.5 V

= 0 → 5 V 3.35 3.70 4.05 V

UVLO Hysteresis 0.25 0.40 0.55 V

Logic Supply Current I

CC(OFF)

Logic Input Voltage V

Logic Input Current I

CC(ON)

IN(1)

IN(0)

IN(1)

IN(0)

D0 = D1 = D2 = D3 = 0.8 V — 14 17 mA

= 2.0 V — <1.0 20 µA

= 0.8 V — <-2.0 -200 µA

—42 50mA

2.0 — — V

— — 0.8 V

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

Continued next page…

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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 (continued)

Mixed-Decay Comparator V Trip Points

PFD

Slow Current-Decay Mode 3.5 — — V

Mixed Current-Decay Mode 1.2 — 2.9 V

Fast Current-Decay Mode — — 0.8 V

Mixed-Decay Comparator V

IO(PFD)

—0±20 mV

Input Offset Voltage

Mixed-Decay Comparator ∆V

IO(PFD)

5.0 25 55 mV

Hysteresis

Reference Input Current I

Reference Divider Ratio V

REF

REF/VS

Digital-to-Analog Converter — 1.0 V < V Accuracy*

Current-Sense Comparator V

IO(S)

= 0 V to 2.5 V — — ±5.0 µA

REF

at trip, D0 = D1 = D2 = D3 = 2 V — 3.0 — —

≤ 2.5 V — — ±3.0 %

REF

0.5 V < V

= 0 V — ±16 — mV

REF

≤ 1.0 V — — ±4.0 %

REF

Input Offset Voltage*

Step Reference SRCR D0 = D1 = D2 = D3 = 0.8 V — 0 — % Current Ratio

D1 = 2 V, D0 = D2 = D3 = 0.8 V — 17.4 — % D0 = D1 = 2 V, D2 = D3 = 0.8 V — 26.1 — % D2 = 2 V, D0 = D1 = D3 = 0.8 V — 34.8 — % D0 = D2 = 2 V, D1 = D3 = 0.8 V — 43.5 — % D1 = D2 = 2 V, D0 = D3 = 0.8 V — 52.2 — % D0 = D1 = D2 = 2 V, D3 = 0.8 V — 60.9 — % D3 = 2 V, D0 = D1 = D2 = 0.8 V — 69.6 — % D0 = D3 = 2 V, D1 = D2 = 0.8 V — 73.9 — % D1 = D3 = 2 V, D0 = D2 = 0.8 V — 78.3 — % D0 = D1 = D3 = 2 V, D2 = 0.8 V — 82.6 — % D2 = D3 = 2 V, D0 = D1 = 0.8 V — 87.0 — % D0 = D2 = D3 = 2 V, D1 = 0.8 V — 91.3 — % D1 = D2 = D3 = 2 V, D0 = 0.8 V — 95.7 — % D0 = D1 = D2 = D3 = 2 V — 100 — %

Thermal Shutdown Temp. T

Thermal Shutdown Hyst. ∆T

* The total error for the V

function is the sum of the D/A error and the current-sense comparator input offset voltage.

REF/VS

— 165 — °C —15—°C

Continued next page…

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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

AC Timing

PWM RC Fixed Off-time t

PWM Turn-Off Time t

PWM Turn-On Time t

PWM Minimum On Time t

Crossover Dead Time t

OFF RC

PWM(OFF)

PWM(ON)

ON(min)

CODT

CT = 470 pF, R

= 43 kΩ 18.2 20.2 22.3 µs

Current-Sense Comparator Trip — 1.0 1.5 µs

to Source OFF, I

= 100 mA

OUT

Current-Sense Comparator Trip — 1.4 2.5 µs

to Source OFF, I

Charge ON to Source ON, — 0.4 0.7 µs

= 100 mA

OUT

Charge ON to Source ON, — 0.55 0.85 µs

= 1.5 A

OUT

VCC = 5.0 V, R

= 100 mA

OUT

T ≥

= 1.5 A

OUT

43 kΩ, CT = 470 pF 1.0 1.6 2.2 µs

1 kΩ Load to 25 V 0.3 1.5 3.0 µs

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

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FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

Typical Operating Characteristics

Source Driver Saturation Voltage

1.5

1.25

1.0

0.75

0.5

0.25

OUTPUT SATURATION VOLTAGE IN VOLTS

0.25

OUTPUT CURRENT IN AMPERES

0.75 1.50.5

SOURCE DRIVER

TJ = +25°C T

= +70°C

= +85°C

= +125°C

1.0 1.25

Dwg. GP-064-2

Satlington™ Sink Driver Saturation Voltage

1.5

1.25

1.0

0.75

0.5

0.25

OUTPUT SATURATION VOLTAGE IN VOLTS

SINK DRIVER

TJ = +25°C T

= +70°C

= +85°C

= +125°C

0.25

OUTPUT CURRENT IN AMPERES

0.75 1.50.5

1.0 1.25

Dwg. GP-064-3

Clamp Diode Forward Voltage

1.5

1.25

1.0

0.75

0.5

FORWARD VOLTAGE IN VOLTS

0.25

FORWARD CURRENT IN AMPERES

Flyback Diode Forward Voltage

1.5

1.25

1.0

0.75

SINK DIODE

TJ = +25°C

= +70°C

T T

= +85°C

= +125°C

0.75 1.50.5

1.0 1.25

Dwg. GD-003-1

0.5

FORWARD VOLTAGE IN VOLTS

0.25

FORWARD CURRENT IN AMPERES

0.75 1.50.5

FLYBACK DIODE

TJ = +25°C

= +70°C

T T

= +85°C

= +125°C

1.0 1.25

Dwg. GD-003-2

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FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

Terminal Functions

A3957SA A3957SLB Terminal

Pin Lead Name Description

– 1 NC No internal connection.

5 2 PFD (Percent Fast Decay) The analog input used to set the current-decay mode.

6 3 REF (V

– 4 NC No internal connection.

7 5 RC The parallel combination of external resistor R

8* 6-7 GROUND Return for the logic supply (V

98 D3(DATA3) One of four (MSB) control bits for the internal digital-to-analog converter.

10 9 LOGIC SUPPLY (VCC) Supply voltage for the logic circuitry. Typically = 5 V.

11 10 PHASE The PHASE input determines the direction of current in the load.

12 11 D

– 12 NC No internal connection.

13 13 D

– 14 NC No internal connection.

14 15 OUT

– 16 NC No internal connection.

15 17 SENSE Connection to the sink-transistor emitters. Sense resistor R

16 – NC No internal connection.

1* 18-19 GROUND Return for the logic supply (V

220 D0(DATA0) One of four (LSB) control bits for the internal digital-to-analog converter.

– 21 NC No internal connection.

3 22 OUT

4 23 LOAD SUPPLY (VBB) Supply voltage for the load.

– 24 NC No internal connection.

) The voltage at this input (along with the value of RS and the states of DAC

REF

inputs D0, D1, and D2) set the peak output current.

and capacitor CT set the off time

for the PWM current regulator. CT also sets the blanking time.

) and load supply (VBB); the reference for all

voltage measurements.

(DATA2) One of four control bits for the internal digital-to-analog converter.

(DATA1) One of four control bits for the internal digital-to-analog converter.

One of two output load connections.

between this point and ground.

voltage measurements.

One of two output load connections.

) and load supply (VBB); the reference for all

is connected

* For the ‘A’ package, pins 1 and 8 must be externally connected together.

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

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FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

Functional Description

Two A3957S— 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 (V converter (DAC) data inputs (D0, D1, D2, and D3).

To improve motor performance, especially when using sinusoidal current profiles necessary for microstepping, the A3957S— 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 1.5 µs prevents crossover currents that could occur when switching the PHASE input.

DAC Data Inputs (D0, D1, D2, D3). 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 D1, D2, and D3 are all logic low, all of the power output transistors are turned off.

Internal PWM Current Control. Each motor driver IC contains an internal fixed off-time PWM current-control circuit that limits the load current to a desired value (I diagonal pair of source and sink transistors are enabled and current flows through the motor winding and RS (figure 1).

Figure 1 — Load-Current Paths

), and the digital-to-analog

REF

DRIVE CURRENT RECIRCULATION

(SLOW-DECAY MODE) RECIRCULATION

(FAST-DECAY MODE)

). Initially, a

TRIP

Dwg. EP-006-15

When the voltage across the sense resistor equals the DAC output voltage, the current-sense comparator 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 V

REF

with a transconductance function approximated by:

TRIP

≈ V

REF

/3RS = I

OUT

+ ISO.

where ISO is the sense-current offset due to the base-drive current of the sink transistor (typically 30 mA). The actual peak load current (I

) will be slightly higher than I

PEAK

TRIP

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 I

again, maintaining an average load current.

TRIP

The current-sense comparator has a fixed offset of approximately 16 mV. With RS = 0.5 Ω, the sense-current offset (ISO) is effectively cancelled (V

≈ ISO • RS).

IO(S)

The DAC data input lines are used to provide up to eight levels of output current. The internal 4-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, eighth-step, or “microstepping” load-current levels.

≈ SRCR x V

TRIP

Slow Current-Decay Mode. When V

/3R

REF

≥ 3.5 V, the device is

PFD

in slow current-decay mode (the source drivers are disabled when the load current reaches I

). During the fixed off time,

TRIP

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 desirable because the average current in the motor winding is more nearly equal to the desired reference value, resulting 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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FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

Under some circumstances slow-decay mode PWM can fail

to maintain good current regulation:

1) The load current will fail to regulate in slow-decay mode due to a sufficiently negative back-EMF voltage in conjunction with the low voltage drop across the load during slow decay recirculation. The negative back-EMF voltage can cause the load current to actually increase during the slow decay off time. A negative back-EMF voltage condition commonly occurs when driving stepping motors because the phase lead of the rotor typically causes the back-EMF voltage to be negative towards the end of each step (see figure 3A).

2) When the desired load current is decreased rapidly, the slow rate of load current decay can prevent the current from following the desired reference value.

3) When the desired load current is set to a very low value, the current-control loop can fail to regulate due to its minimum duty cycle, which is a function of the userselected value of t width t

that occurs each time the PWM latch is reset.

on(min)

Fast Current-Decay Mode. When V

and the minimum on-time pulse

OFF

≤ 0.8 V, the device is

PFD

in fast current-decay mode (both the sink and source drivers are disabled when the load current reaches I

). During the fixed

TRIP

off time, the load inductance causes the current to flow from ground to the load supply via the motor winding, ground-clamp and flyback diodes (see figure 1). Because the full motor supply voltage is across the load during fast-decay recirculation, the rate of load current decay is rapid, producing a high ripple current for a given fixed off time (see figure 2). This rapid rate of decay allows good current regulation to be maintained at the

TRIP

PEAK

SLOW (V ≥ 3.5 V)

PFD

A — Slow-Decay Mode

B — Fast-Decay Mode

MIXED (1.2 V ≤ V ≤ 2.9 V)

FAST (V ≤ 0.8 V)

PFD

OFF

PFD

Figure 2 — Current-Decay Waveforms

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

PFD

Dwg. WP-031-2

C — Mixed-Decay Mode

Figure 3 — Sinusoidal Drive Currents

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cost of decreased average current accuracy or increased driver and motor losses.

Mixed Current-Decay Mode. If V

is between 1.2 V and

PFD

2.9 V, the device will be in a mixed current-decay mode. Mixed-decay mode allows the user to achieve good current regulation with a minimum amount of ripple current and motor/ driver losses by selecting the minimum percentage of fast decay required for their application (see also Stepper Motor Applications).

As in fast current-decay mode, mixed-decay starts with the sink and source drivers disabled after the load current reaches I

TRIP

When the voltage at the RC terminal decays to a value below V

, the sink drivers are re-enabled, placing the device in slow

PFD

current-decay mode for the remainder of the fixed off time (figure 2). The percentage of fast decay (PFD) is user determined by V

or two external resistors.

PFD

PFD = 100 ln (0.6[R1+R2]/R2)

where

PFD

Dwg. EP-062-1

Fixed Off-Time. The internal PWM current-control circuitry uses a one shot to control the time the driver(s) remain(s) off. The one-shot off-time, t

, is determined by the selection of an

OFF

external resistor (RT) and capacitor (CT) connected from the RC timing terminal to ground. The off-time, over a range of values of CT = 470 pF to 1500 pF and RT = 12 kΩ to 100 kΩ, is approximated by:

≈ RTCT.

OFF

When the load current is increasing, but has not yet reached the sense-current comparator threshold (I the RC terminal is approximately 0.6VCC. When I

), the voltage on

TRIP

is reached, the PWM latch is reset by the current-sense comparator and the voltage on the RC terminal will decay until it reaches approximately 0.22VCC. The PWM latch is then set, thereby re-enabling the driver(s) and allowing load current to increase again. The PWM cycle repeats, maintaining the peak load current at the desired value.

With increasing values of t

switching losses will

OFF,

decrease, low-level load-current regulation will improve, EMI will be reduced, the PWM frequency will decrease, and ripple current will increase. A value of t

can be chosen for optimi-

OFF

zation of these parameters. For applications where audible noise is a concern, typical values of t

are chosen to be in the

OFF

range of 15 µs to 35 µs. RC Blanking. In addition to determining the fixed off-time of

the PWM control circuit, the CT component sets the comparator blanking time. This function blanks the output of the currentsense comparator when the outputs are switched by the internal

current-control circuitry (or by the PHASE input, or when the device is enabled with the DAC data inputs). The comparator output is blanked to prevent false over-current detections due to reverse recovery currents of the clamp diodes, and/or switching transients related to distributed capacitance in the load.

During internal PWM operation, at the end of the t the comparator’s output is blanked and CT begins to be charged from approximately 0.22VCC by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 0.6VCC. The blanking time, t

, can be calculated as:

BLANK

= RTCT ln (RT/[RT - 3 kΩ]).

BLANK

When a transition of the PHASE input occurs, CT is discharged to near ground during the crossover delay time (the crossover delay time is present to prevent simultaneous conduction of the source and sink drivers). After the crossover delay, CT is charged by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 0.6VCC.

Similarly, when the device is disabled, via the DAC data inputs, CT is discharged to near ground. When the device is reenabled, CT is charged by an internal current source of approximately 1 mA. The comparator output remains blanked until the voltage on CT reaches approximately 0.6VCC. The blanking time, t

′, can be calculated as:

BLANK

′ ≈ 1900 CT.

The minimum recommended value for CT is 470 pF ± 5 %. This value ensures that the blanking time is sufficient to avoid false trips of the comparator under normal operating conditions. For optimal regulation of the load current, this value for CT is recommended and the value of RT can be sized to determine t

OFF

time,

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Thermal Considerations. Thermal-protection circuitry turns off all output transistors when the junction temperature reaches approximately +165°C. This is intended only to protect the device from failures due to excessive junction temperatures and should not imply that output short circuits are permitted. The output transistors are re-enabled when the junction temperature cools to approximately +150°C.

Stepper Motor Applications. The A3957SB or A3957SLB are used to optimize performance in microstepping/sinusoidal

PHASE

PFD

REF

470 pF

+5 V

BRIDGE A

NC NC

322

30 kΩ

10 15

LOGIC

47 µF

0.5 Ω

stepper-motor drive applications (see figures 4 and 5). When the load current is increasing, the slow current-decay mode is used to limit the switching losses in the driver and iron losses in the motor. This also improves the maximum rate at which the load current can increase (as compared to fast decay) due to the slow rate of decay during t

. When the load current is

OFF

decreasing, the mixed current-decay mode is used to regulate the load current to the desired level. This prevents tailing of the current profile caused by the back-EMF voltage of the stepper motor (see figure 3A).

BRIDGE B

47 µF

0.5 Ω

LOGIC

NCNC

1015

322

PHASE

+5 V

30 kΩ

470 pF

REF

PFD

Dwg. EP-047-5

Figure 4 — Typical Application

MIXED DECAY

SLOW DECAYSLOW DECAY MIXED DECAY

Figure 5 — Microstepping/Sinusoidal Drive Current

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

Dwg. WK-004-5

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Table 4 — Step Sequencing

Full1/21/41/81/16

Step Step Step Step Step

11111 H H H H H100% X L L L X 0% 0°

2 3 H H H H H 100% H L L H H 26.1%

2 3 5 H H H L H 91.3% H L H L H 43.5%

4 7 H H L H H 82.6% H L H H H 60.9%

2359 H H L L H73.9% H H L L H 73.9% 45°

6 11 H L H H H 60.9% H H L H H 82.6%

4 7 13 H L H L H 43.5% H H H L H 91.3%

8 15 H L L H H 26.1% H H H H H 100%

235917 X L L L X 0% H H H H H100% 90°

10 19 L L L H H -26.1% H H H H H 100%

6 11 21 L L H L H -43.5% H H H L H 91.3%

12 23 L L H H H -60.9% H H L H H 82.6%

4 7 13 25 L H L L H -73.9% H H L L H 73.9% 135°

14 27 L H L H H -82.6% H L H H H 60.9%

8 15 29 L H H L H -91.3% H L H L H 43.5%

16 31 L H H H H -100% H L L H H 26.1%

3 5 9 17 33 L H H H H -100% X L L L X 0% 180°

18 35 L H H H H -100% L L L H H -26.1%

10 19 37 L H H L H -91.3% L L H L H -43.5%

20 39 L H L H H -82.6% L L H H H -60.9%

6 11 21 41 L H L L H -73.9% L H L L H -73.9% 225°

22 43 L L H H H -60.9% L H L H H -82.6%

12 23 45 L L H L H -43.5% L H H L H -91.3%

24 47 L L L H H -26.1% L H H H H -100%

4 7 13 25 49 X L L L X 0% L H H H H -100% 270°

26 51 H L L H H 26.1% L H H H H -100%

14 27 53 H L H L H 43.5% L H H L H -91.3%

28 55 H L H H H 60.9% L H L H H -82.6%

8 15 29 57 H H L L H 73.9% L H L L H -73.9% 315°

30 59 H H L H H 82.6% L L H H H -60.9%

16 31 61 H H H L H 91.3% L L H L H -43.5%

32 63 H H H H H 100% L L L H H -26.1%

PHASE

2 H H H H H 100% H L L H L 17.4%

4 H H H H L 95.7% H L H L L 34.8%

6 H H H L L 87.0% H L H H L 52.2%

8 H H L H L 78.3% H H L L L 69.6%

10 H H L L L 69.6% H H L H L 78.3%

12 H L H H L 52.2% H H H L L 87.0%

14 H L H L L 34.8% H HHHL95.7%

16 H L L H L 17.4% H H H H H 100%

18 L L L H L -17.4% H H H H H 100%

20 L L H L L -34.8% H HHHL95.7%

22 L L H H L -52.2% H H H L L 87.0%

24 L H L L L -69.6% H H L H L 78.3%

26 L H L H L -78.3% H H L L L 69.6%

28 L H H L L -87.0% H L H H L 52.2%

30 L H H H L -95.7% H L H L L 34.8%

32 L H H H H -100% H L L H L 17.4%

34 L H H H H -100% L L L H L -17.4%

36 L H H H L -95.7% L L H L L -34.8%

38 L H H L L -87.0% L L H H L -52.2%

40 L H L H L -78.3% L H L L L -69.6%

42 L H L L L -69.6% L H L H L -78.3%

44 L L H H L -52.2% L H H L L -87.0%

46 L L H L L -34.8% L HHHL-95.7%

48 L L L H L -17.4% L H H H H -100%

50 H L L H L 17.4% L H H H H -100%

52 H L H L L 34.8% L HHHL-95.7%

54 H L H H L 52.2% L H H L L -87.0%

56 H H L L L 69.6% L H L H L -78.3%

58 H H L H L 78.3% L H L L L -69.6%

60 H H H L L 87.0% L L H H L -52.2%

62 H H H H L 95.7% L L H L L -34.8%

64 H H H H H 100% L L L H L -17.4%

AD3AD2AD1AD0AILOAD A

Bridge A Bridge B

PHASEBD

3BD2BD1BD0BILOAD B

angle

Step

Page 14

3957

FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

0.280

0.240

A3957SA

Dimensions in Inches

(controlling dimensions)

0.014

0.008

0.300

BSC

0.430

MAX

0.210

MAX

7.11

6.10

0.015

MIN

0.070

0.045

1.77

1.15

0.022

0.014

0.150

0.115

0.775

0.735

0.100

BSC

Dimensions in Millimeters

(for reference only)

19.68

18.67

2.54

BSC

0.005

MIN

0.13

MIN

0.355

0.204

Dwg. MA-001-16A in

10.92

MAX

7.62

BSC

5.33

MAX

0.39

MIN

0.558

0.356

3.81

2.93

NOTES:1. Exact body and lead configuration at vendor’s option within limits shown.

2. Lead spacing tolerance is non-cumulative

3. Lead thickness is measured at seating plane or below.

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

Dwg. MA-001-16A mm

Page 15

3957

FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

A3957SLB

Dimensions in Inches

(for reference only)

0.2992

0.2914

0.020

0.013

0.0926

0.1043

24 13

1 2

0.6141

0.5985

0.0040

MIN

Dimensions in Millimeters

(controlling dimensions)

24 13

0.050

BSC

NOTE 1 NOTE 3

0.0125

0.0091

0.491

0.394

0.050

0.016

0° TO 8

Dwg. MA-008-25 in

0.32

0.23

7.60

7.40

0.51

0.33

1 2

15.60

15.20

1.27

BSC

NOTE 1 NOTE 3

10.65

10.00

2.65

2.35

0.10

MIN

NOTES:1. Exact body and lead configuration at vendor’s option within limits shown.

2. Lead spacing tolerance is non-cumulative

3. Webbed lead frame. Leads 4, 5, 12, and 13 are internally one piece.

1.27

0.40

0° TO 8

Dwg. MA-008-25A mm

Page 16

3957

FULL-BRIDGE PWM MICROSTEPPING MOTOR DRIVER

Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the design of its products.

The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.

115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000