LMD18201
3A, 55V H-Bridge

General Description

The LMD18201 is a 3A H-Bridge designed for motion control
applications. The device is built using a multi-technology pro-
cess which combines bipolar and CMOS control circuitry
with DMOS power devices on the same monolithic structure.
The H-Bridge configuration is ideal for driving DC and step-
per motors. The LMD18201 accommodates peak output cur-
rents up to 6A. Current sensing can be achieved via a small
sense resistor connected in series with the power ground
lead. For current sensing without disturbing the path of cur-
rent to the load, the LMD18200 is recommended.

Features

Delivers up to 3A continuous output

Operates at supply voltages up to 55V

Low R

DS(ON)

typically 0.33

per switch

TTL and CMOS compatible inputs

No "shoot-through" current

Thermal warning flag output at 145°C

Thermal shutdown (outputs off) at 170°C

Internal clamp diodes

Shorted load protection

Internal charge pump with external bootstrap capability

Applications

DC and stepper motor drives

Position and velocity servomechanisms

Factory automation robots

Numerically controlled machinery

Computer printers and plotters

Functional Diagram

DS010793-1

FIGURE 1. Functional Block Diagram of LMD18201

April 1998

LMD18201

3A,

55V

H-Bridge

DS010793

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Absolute Maximum Ratings

(Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Total Supply Voltage (V

, Pin 6)

60V

Voltage at Pins 3, 4, 5 and 9

12V

Voltage at Bootstrap Pins (Pins 1 and 11)

OUT

+ 16V

Peak Output Current (200 ms)

Continuous Output Current (Note 2)

Power Dissipation (Note 3)

25W

Sense Voltage (Pin 7 to Pin 8)

+0.5V to -1.0V

Power Dissipation (T

= 25°C, Free Air)

Junction Temperature, T

J(max)

150°C

ESD Susceptibility (Note 4)

1500V

Storage Temperature, T

STG

-40°C to +150°C

Lead Temperature (Soldering, 10 sec.)

300°C

Operating Ratings

(Note 1)

Junction Temperature, T

-40°C to +125°C

Supply Voltage

+12V to +55V

Electrical Characteristics

(Note 5)

The following specifications apply for V

= 42V, unless otherwise specified. Boldface limits apply over the entire operating

temperature range, -40°C

+125°C, all other limits are for T

= T

= 25°C.

Symbol

Parameter

Conditions

Typ

Limit

Units

DS(ON)

Switch ON Resistance

Output Current = 3A (Note 6)

0.33

0.4/0.6

(max)

DS(ON)

Switch ON Resistance

Output Current = 6A (Note 6)

0.33

0.4/0.6

(max)

CLAMP

Clamp Diode Forward Drop

Clamp Current = 3A (Note 6)

1.2

1.5

V (max)

Logic Low Input Voltage

Pins 3, 4, 5

-0.1

V (min)

0.8

V (max)

Logic Low Input Current

= -0.1V, Pins = 3, 4, 5

-10

µA (max)

Logic High Input Voltage

Pins 3, 4, 5

V (min)

V (max)

Logic High Input Current

= 12V, Pins = 3, 4, 5

µA (max)

Undervoltage Lockout

Outputs Turn OFF

V (min)

V (max)

Warning Flag Temperature

Pin 9

0.8V, I

= 2 mA

145

°C

F(ON)

Flag Output Saturation Voltage

= T

, I

= 2 mA

0.15

F(OFF)

Flag Output Leakage

= 12V

0.2

µA (max)

JSD

Shutdown Temperature

Outputs Turn OFF

170

°C

Quiescent Supply Current

All Logic Inputs Low

mA (max)

D(ON)

Output Turn-On Delay Time

Sourcing Outputs, I

OUT

= 3A

300

Sinking Outputs, I

OUT

= 3A

300

Output Turn-On Switching Time

Bootstrap Capacitor = 10 nF

Sourcing Outputs, I

OUT

= 3A

100

Sinking Outputs, I

OUT

= 3A

D(OFF)

Output Turn-Off Delay Times

Sourcing Outputs, I

OUT

= 3A

200

Sinking Outputs, I

OUT

= 3A

200

OFF

Output Turn-Off Switching Times

Bootstrap Capacitor = 10 nF

Sourcing Outputs, I

OUT

= 3A

Sinking Outputs, I

OUT

= 3A

Minimum Input Pulse Width

Pins 3, 4 and 5

µs

CPR

Charge Pump Rise Time

No Bootstrap Capacitor

µs

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating
the device beyond its rated operating conditions.

Note 2: See Application Information for details regarding current limiting.

Note 3: The maximum power dissipation must be derated at elevated temperatures and is a function of T

J(max)

, and T

. The maximum allowable power dissi-

pation at any temperature is P

D(max)

= (T

J(max)

- T

, or the number given in the Absolute Ratings, whichever is lower. The typical thermal resistance from junction

to case (

) is 1.0°C/W and from junction to ambient (

) is 30°C/W. For guaranteed operation T

J(max)

= 125°C.

Note 4: Human-body model, 100 pF discharged through a 1.5 k

resistor. Except Bootstrap pins (pins 1 and 11) which are protected to 1000V of ESD.

Note 5: All limits are 100% production tested at 25°C. Temperature extreme limits are guaranteed via correlation using accepted SQC (Statistical Quality Control)
methods. All limits are used to calculate AOQL, (Average Outgoing Quality Level).

Note 6: Output currents are pulsed (t

2 ms, Duty Cycle

5%).

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Pinout Description

(See Connection Diagram)

Pin 1, BOOTSTRAP 1 Input: Bootstrap capacitor pin for half
H-Bridge number 1. The recommended capacitor (10 nF) is
connected between pins 1 and 2.

Pin 2, OUTPUT 1: Half H-Bridge number 1 output.

Pin 3, DIRECTION Input: See

Table 1. This input controls

the direction of current flow between OUTPUT 1 and OUT-
PUT 2 (pins 2 and 10) and, therefore, the direction of rotation
of a motor load.

Pin 4, BRAKE Input: See

Table 1. This input is used to

brake a motor by effectively shorting its terminals. When
braking is desired, this input is taken to a logic high level and
it is also necessary to apply logic high to PWM input, pin 5.
The drivers that short the motor are determined by the logic
level at the DIRECTION input (Pin 3): with Pin 3 logic high,
both current sourcing output transistors are ON; with Pin 3
logic low, both current sinking output transistors are ON. All
output transistors can be turned OFF by applying a logic high
to Pin 4 and a logic low to PWM input Pin 5; in this case only
a small bias current (approximately -1.5 mA) exists at each
output pin.

Pin 5, PWM Input: See

Table 1. How this input (and DIREC-

TION input, Pin 3) is used is determined by the format of the
PWM Signal.

Pin 6, V

Power Supply

Pin 7, POWER GROUND/SENSE Connection: This pin is
the ground return for the power DMOS transistors of the
H-Bridge. The current through the H-Bridge can be sensed
by adding a small, 0.1

, sense resistor from this pin to the

power supply ground.

Pin 8, SIGNAL GROUND: This is the ground return for the
internal logic circuitry used to control the PWM switching of
the H-Bridge.

Pin 9, THERMAL FLAG Output: This pin provides the ther-
mal warning flag output signal. Pin 9 becomes active-low at
145°C (junction temperature). However the chip will not shut
itself down until 170°C is reached at the junction.

Pin 10, OUTPUT 2: Half H-Bridge number 2 output.

Pin 11, BOOTSTRAP 2 Input: Bootstrap capacitor pin for
half H-Bridge number 2. The recommended capacitor
(10 nF) is connected between pins 10 and 11.

TABLE 1. Logic Truth Table

PWM

Dir

Brake

Active Output Drivers

Source 1, Sink 2

Sink 1, Source 2

Source 1, Source 2

Sink 1, Sink 2

NONE

Application Information

TYPES OF PWM SIGNALS

The LMD18201 readily interfaces with different forms of
PWM signals. Use of the part with two of the more popular
forms of PWM is described in the following paragraphs.

Simple, locked anti-phase PWM consists of a single, vari-
able duty-cycle signal in which is encoded both direction and

amplitude information (see

Figure 2). A 50% duty-cycle

PWM signal represents zero drive, since the net value of
voltage (integrated over one period) delivered to the load is
zero. For the LMD18201, the PWM signal drives the direc-
tion input (pin 3) and the PWM input (pin 5) is tied to logic
high.

Sign/magnitude PWM consists of separate direction (sign)
and amplitude (magnitude) signals (see

Figure 3). The (ab-

solute) magnitude signal is duty-cycle modulated, and the
absence of a pulse signal (a continuous logic low level) rep-
resents zero drive. Current delivered to the load is propor-
tional to pulse width. For the LMD18201, the DIRECTION in-
put (pin 3) is driven by the sign signal and the PWM input
(pin 5) is driven by the magnitude signal.

USING THE THERMAL WARNING FLAG

The THERMAL FLAG output (pin 9) is an open collector tran-
sistor. This permits a wired OR connection of thermal warn-
ing flag outputs from multiple LMD18201's, and allows the
user to set the logic high level of the output signal swing to
match system requirements. This output typically drives the
interrupt input of a system controller. The interrupt service
routine would then be designed to take appropriate steps,
such as reducing load currents or initiating an orderly system
shutdown. The maximum voltage compliance on the flag pin
is 12V.

SUPPLY BYPASSING

During switching transitions the levels of fast current
changes experienced may cause troublesome voltage tran-
sients across system stray inductances.

It is normally necessary to bypass the supply rail with a high
quality capacitor(s) connected as close as possible to the V

Power Supply (Pin 6) and POWER GROUND (Pin 7). A 1 µF
high-frequency ceramic capacitor is recommended. Care
should be taken to limit the transients on the supply pin be-
low the Absolute Maximum Rating of the device. When oper-
ating the chip at supply voltages above 40V a voltage sup-
pressor (transorb) such as P6KE62A is recommended from

DS010793-4

FIGURE 2. Locked Anti-Phase PWM Control

DS010793-5

FIGURE 3. Sign/Magnitude PWM Control

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Application Information

(Continued)

supply to ground. Typically the ceramic capacitor can be
eliminated in the presence of the voltage suppressor. Note
that when driving high load currents a greater amount of sup-
ply bypass capacitance (in general at least 100 µF per Amp
of load current) is required to absorb the recirculating cur-
rents of the inductive loads.

CURRENT LIMITING

Current limiting protection circuitry has been incorporated
into the design of the LMD18201. With any power device it is
important to consider the effects of the substantial surge cur-
rents through the device that may occur as a result of
shorted loads. The protection circuitry monitors the current
through the upper transistors and shuts off the power device
as quickly as possible in the event of an overload condition
(the threshold is set to approximately 10A). In a typical motor
driving application the most common overload faults are
caused by shorted motor windings and locked rotors. Under
these conditions the inductance of the motor (as well as any
series inductance in the V

supply line) serves to reduce

the magnitude of a current surge to a safe level for the
LMD18201. Once the device is shut down, the control cir-
cuitry will periodically try to turn the power device back on.
This feature allows the immediate return to normal operation
once the fault condition has been removed. While the fault
remains however, the device will cycle in and out of thermal
shutdown. This can create voltage transients on the V

supply line and therefore proper supply bypassing tech-
niques are required.

The most severe condition for any power device is a direct,
hard-wired ("screwdriver") long term short from an output to
ground. This condition can generate a surge of current
through the power device on the order of 15 Amps and re-
quire the die and package to dissipate up to 500W of power
for the short time required for the protection circuitry to shut
off the power device. This energy can be destructive, particu-
larly at higher operating voltages (

30V) so some precau-

tions are in order. Proper heat sink design is essential and it
is normally necessary to heat sink the V

supply pin (pin 6)

with 1 square inch of copper on the PC board.

INTERNAL CHARGE PUMP AND USE OF
BOOTSTRAP CAPACITORS

To turn on the high-side (sourcing) DMOS power devices,
the gate of each device must be driven approximately 8V
more positive than the supply voltage. To achieve this an in-
ternal charge pump is used to provide the gate drive voltage.
As shown in (

Figure 4), an internal capacitor is alternately

switched to ground and charged to about 14V, then switched
to V

thereby providing a gate drive voltage greater than V

This switching action is controlled by a continuously running
internal 300 kHz oscillator. The rise time of this drive voltage
is typically 20 µs which is suitable for operating frequencies
up to 1 kHz.

For higher switching frequencies, the LMD18201 provides
for the use of external bootstrap capacitors. The bootstrap
principle is in essence a second charge pump whereby a
large value capacitor is used which has enough energy to
quickly charge the parasitic gate input capacitance of the
power device resulting in much faster rise times. The switch-
ing action is accomplished by the power switches them-
selves (

Figure 5). External 10 nF capacitors, connected from

the outputs to the bootstrap pins of each high-side switch
provide typically less than 100 ns rise times allowing switch-
ing frequencies up to 500 kHz.

INTERNAL PROTECTION DIODES

A major consideration when switching current through induc-
tive loads is protection of the switching power devices from
the large voltage transients that occur. Each of the four
switches in the LMD18201 have a built-in protection diode to
clamp transient voltages exceeding the positive supply or
ground to a safe diode voltage drop across the switch.

The reverse recovery characteristics of these diodes, once
the transient has subsided, is important. These diodes must
come out of conduction quickly and the power switches must
be able to conduct the additional reverse recovery current of
the diodes. The reverse recovery time of the diodes protect-
ing the sourcing power devices is typically only 70 ns with a
reverse recovery current of 1A when tested with a full 3A of
forward current through the diode. For the sinking devices
the recovery time is typically 100 ns with 4A of reverse cur-
rent under the same conditions.

DS010793-6

FIGURE 4. Internal Charge Pump Circuitry

DS010793-7

FIGURE 5. Bootstrap Circuitry

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Typical Applications

BASIC MOTOR DRIVER

The LMD18201 can directly interface to any Sign/Magnitude
PWM controller. The LM629 is a motion control processor
that outputs a Sign/Magnitude PWM signal to coordinate ei-

ther positional or velocity control of DC motors. The
LMD18201 provides fully protected motor driver stage.

CURRENT SENSING

In many motor control applications it is desirable to sense
and control the current through the motor. For these types of
applications a companion product, the LMD18200, is also
available. The LMD18200 is identical to the LMD18201 but
has current sensing transistors that output a current directly
proportional to the current conducted by the two upper
DMOS power devices to a separate current sense pin. This
technique does not require a low valued, power sense resis-
tor and does not subtract from the available voltage drive to
the motor.

To sense the bridge current through the LMD18201 requires
the addition of a small sense resistor between the power
ground/sense pin (Pin 7) and the actual circuit ground (see
Figure 7). This resistor should have a value of 0.1

or less to

stay within the allowable voltage compliance of the sense
pin, particularly at higher operating current levels. The volt-
age between power ground/sense (Pin 7) and the signal
ground (Pin 8) must stay within the range of -1V to +0.5V. In-
ternally there is approximately 25

between pins 7 and 8

and this resistance will slightly reduce the value of the exter-
nal sense resistor. Approximately 70% of the quiescent sup-
ply current (10 mA) flows out of pin 7. This will cause a slight
offset to the voltage across the sense resistor when the
bridge is not conducting. During reverse recovery of the in-
ternal protection diodes the voltage compliance between
pins 7 and 8 may be exceeded. The duration of these spikes
however are only approximately 100 ns and do not have
enough time or energy to disrupt the operation of the
LMD18201.

DS010793-10

FIGURE 6. Basic Motor Driver

DS010793-11

FIGURE 7. Current Sensing

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Physical Dimensions

inches (millimeters) unless otherwise noted

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11-Lead TO-220 Power Package (T)

Order Number LMD18201T

NS Package Number TA11B

LMD18201

3A,

55V

H-Bridge

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

Part Number LMD18201