A3964SLB Datasheet A3964SB, A3964SLB | P4-P6

3964

DUAL FULL-BRIDGE

PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

Logic Supply Voltage Range V

Operating 4.75 — 5.25 V

Logic Input Voltage V

IN(1)

2.4 — — V

IN(0)

— — 0.8 V

Logic Input Current I

IN(1)

= 2.4 V — <1.0 20 µA

IN(0)

= 0.8 V — <-2.0 -200 µA

Reference Output Voltage V

REF(OUT)

= 5.0 V, I

REF(OUT)

= 90 to 900 µA 2.45 2.50 2.55 V

Reference Output Current I

REF(OUT)

3 kΩ ≤ R

= R

+ R

≤ 15 kΩ 150 — 900 µA

Ref. Input Offset Current I

REF(IN)

= 1 V -2.5 0 1.0 µA

Comparator Input Offset Volt. V

REF(IN)

= 0 V -6.0 0 6.0 mV

Comparator Input Volt. Range V

REF

Operating -0.3 — 1.0 V

PWM RC Fixed Off-time t

OFF RC

= 1000 pF, R

= 30 kΩ 27 30 33 µs

PWM Propagation Delay Time t

PWM

Comparator Trip to Source OFF — 1.2 2.0 µs

PWM Minimum On Time t

ON(min)

= 1000 pF, R

≥

15 kΩ, V

= 5 V — 2.5 3.6 µs

Propagation Delay Times t

OUT

= ±800 mA, 50% to 90%:

ENABLE ON to Source ON — 3.2 — µs

ENABLE OFF to Source OFF — 1.2 — µs

ENABLE ON to Sink ON — 3.2 — µs

ENABLE OFF to Sink OFF — 0.7 — µs

PHASE Change to Sink ON — 3.2 — µs

PHASE Change to Source ON — 3.2 — µs

PHASE Change to Sink OFF — 0.7 — µs

PHASE Change to Source OFF — 1.2 — µs

Thermal Shutdown Temp. T

— 165 — °C

Thermal Shutdown Hysteresis ∆T

—15—°C

UVLO Disable Threshold Decreasing V

4.20 4.40 4.65 V

UVLO Hysteresis UVLO Enable Volt. - UVLO Disable Volt. 0.075 0.125 0.175 V

UVLO Enable Threshold Increasing V

4.375 4.525 4.725 V

Logic Supply Current I

CC(ON)

ENABLE 1

= V

ENABLE 2

= 0.8 V — 60 85 mA

CC(OFF)

ENABLE 1

= V

ENABLE 2

= 2.4 V — 13 17 mA

Logic Supply Current ∆I

CC(ON)

ENABLE 1

ENABLE 2

= 0.8 V — 0.18 — mA/°C

Temperature Coefficient

Limits

Characteristic Symbol Test Conditions Min. Typ. Max. Units

ELECTRICAL CHARACTERISTICS at T

= +25°C, V

= 30 V, V

= 4.75 V to 5.25 V, V

SENSE

= 0

V, 30 kΩ & 1000 pF RC to Ground (unless noted otherwise) (cont.)

NOTES: 1. Typical Data is for design information only.

2. Negative current is defined as coming out of (sourcing) the specified device terminal.

Control Logic

3964

DUAL FULL-BRIDGE

PWM MOTOR DRIVER

[(V

– V

SAT(SOURCE+SINK)

) • t

ON(min)

max] – (1.05 (V

SAT(SINK)

+ V

) • t

OFF

)

1.05 (t

ON(min)

max + t

OFF

) • R

LOAD

AVG

≈

FUNCTIONAL DESCRIPTION

Internal PWM Current Control. The A3964SB and

A3964SLB contain a fixed off-time pulse-width modulated

(PWM) current-control circuit that can be used to limit the

load current to a desired value. The peak value of the

current limiting (I

TRIP

) is set by the selection of an external

current-sensing resistor (R

) and reference input voltage

REF(IN)

). The internal circuitry compares the voltage

across the external sense resistor to the voltage on the

reference input terminal (V

REF(IN)

) resulting in a

transconductance function approximated by:

The reference input voltage is typically set with a

resistor divider from V

REF(OUT)

. To ensure proper operation

of the voltage reference, the resistor divider should have

an impedance of 3 kΩ to 15 kΩ (R

= R

). Within this

range, a low impedance will minimize the effect of the REF

IN input offset current.

The current-control circuitry limits the load current as

follows: when the load current reaches I

TRIP

, the compara-

tor resets a latch that turns off the selected source driver.

The load inductance causes the current to recirculate

through the sink driver and flyback diode.

For each bridge, the user selects an external resistor

) and capacitor (C

) to determine the time period

OFF

= R

) during which the source driver remains

disabled (see “RC Fixed Off-time” below). The range of

recommended values for C

and R

are 1000 pF to 1500

pF and 15 kΩ to 100 kΩ respectively. For optimal load

current regulation, C

is normally set to 1000 pF (see

“Load Current Regulation” below). At the end of the RC

interval, the source driver is enabled allowing the load

current to increase again. The PWM cycle repeats,

maintaining the peak load current at the desired value.

RC Blanking. In addition to determining the fixed off-time

of the PWM control circuit, the C

component sets the

comparator blanking time. This function blanks the output

of the comparator when the outputs are switched by the

internal current-control circuitry (or by the PHASE or

ENABLE inputs). The comparator output is blanked to

TRIP

≈

REF(IN)

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

OFF

time, the comparator’s output is blanked and C

begins to

be charged from approximately 1.1 volts by an internal

current source of approximately 1 mA. The comparator

output remains blanked until the voltage on C

reaches

approximately 3 volts.

When a transition of the PHASE input occurs, C

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, C

is charged by an internal

current source of approximately 1 mA. The comparator

output remains blanked until the voltage on C

reaches

approximately 3 volts.

When the device is disabled, via the ENABLE input,

is discharged to near ground. When the device is

re-enabled, C

is charged by an internal current source of

approximately 1 mA. The comparator output remains

blanked until the voltage on C

reaches approximately

3 volts.

The minimum recommended value for C

1000 pF. 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, the above value for C

is recommended and

the value of R

can be sized to determine t

OFF

. For more

information regarding load current regulation, see below.

Load Current Regulation. Because the device operates

in a slow current-decay mode (2-quadrant PWM mode),

there is a limit to the lowest level that the PWM current

control circuitry can regulate load current. The limitation is

due to the minimum PWM duty cycle, which is a function of

the user-selected value of t

OFF

and the minimum on-time

pulse t

ON(min)

max that occurs each time the PWM latch is

reset. If the motor is not rotating, as in the case of a

stepper motor in hold/detent mode, a brush dc motor when

stalled or at startup, the worst case value of current

regulation can be approximated by:

3964

DUAL FULL-BRIDGE

PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

dc servo motor applications as the transfer function

between the duty cycle on the PHASE input and the

average voltage applied to the motor is more linear than in

the case of ENABLE PWM control (which produces a

discontinuous current at low current levels).

Miscellaneous Information. An internally generated

dead time prevents crossover currents that can occur

when switching phase.

Thermal protection circuitry turns OFF all drivers

should the junction temperature reach +165°C (typical).

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 hyster-

esis of the thermal shutdown circuit is approximately 15°C.

APPLICATION NOTES

Current Sensing. The actual peak load current (I

PEAK

) will

be above the calculated value of I

TRIP

due to delays in the

turn off of the drivers. The amount of overshoot can be

approximated by:

where V

is the motor supply voltage, V

BEMF

is the back-

EMF voltage of the load, R

LOAD

and L

LOAD

are the resis-

tance and inductance of the load respectively, and t

PWM

specified in the electrical characteristics table.

To minimize current sensing inaccuracies caused by

ground trace IR drops, each current-sensing resistor

should have a separate return to the ground terminal of the

device. For low-value sense resistors, the IR drops in the

PCB can be significant and should be taken into account.

The use of sockets should be avoided as their contact

resistance can cause variations in the effective value of

Generally, larger values of R

reduce the aforemen-

tioned effects but can result in excessive heating and

power loss in the sense resistor. The selected value of R

should not cause the absolute maximum voltage rating of

1.0 V, for the SENSE terminal, to be exceeded. The

recommended value of R

is in the range of:

where t

OFF

= R

, R

LOAD

is the series resistance of the

load, V

is the motor supply voltage and t

ON(min)

max

specified in the electrical characteristics table. When the

motor is rotating, the back EMF generated will influence

the above relationship. For brush dc motor applications,

the current regulation is improved. For stepper motor

applications when the motor is rotating, the effect is

dependent on the polarity and magnitude of the motor’s

back EMF.

The following procedure can be used to evaluate the

worst case internal PWM load current regulation in the

system:

Set V

REF(IN)

to 0 volts. With the load connected and the

PWM current control operating in slow decay mode, use

an oscilloscope to measure the time the output is low

(sink ON) for the output that is chopping. This is the

typical minimum on time (t

ON(min)

typ) for the device. The

then should be increased until the measured value of

ON(min)

is equal to t

ON(min)

max as specified in the electri-

cal characteristics table. When the new value of C

has

been set, the value of R

should be decreased so the

value for t

OFF

= R

(with the artificially increased value

of C

) is equal to the nominal design value. The worst-

case load-current regulation then can be measured in

the system under operating conditions.

PWM of the Phase and Enable Inputs. The PHASE and

ENABLE inputs can be pulse width modulated to regulate

load current. Typical propagation delays from the PHASE

and ENABLE inputs to transitions of the power outputs are

specified in the electrical characteristics table. If the

internal PWM current control is used, the comparator

blanking function is active during phase and enable

transitions. This eliminates false tripping of the over-

current comparator caused by switching transients

(see “RC Blanking” above).

Enable PWM. Toggling the ENABLE input turns ON and

OFF the selected source and sink drivers. The corre-

sponding pair of flyback and ground clamp diodes conduct

after the drivers are disabled, resulting in fast current

decay. When the device is enabled the internal current

control circuitry will be active and can be used to limit the

load current in a slow current-decay mode.

Phase PWM. Toggling the PHASE terminal selects which

sink/source pair is enabled, producing a load current that

varies with the duty cycle and remains continuous at all

times. This can have added benefits in bidirectional brush

– [(I

TRIP

• R

LOAD

) + V

BEMF

]) • t

PWM

LOAD

≈

0.5

TRIP

max

≈± 50%

P1-P3 P4-P6 P7-P9 P10-P10

A3964SLB

Mfr. #:

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A3964SLB

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