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PDF LMD18245T Data sheet ( Hoja de datos )
| Número de pieza | LMD18245T | |
| Descripción | 3A / 55V DMOS Full-Bridge Motor Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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April 1998
LMD18245
3A, 55V DMOS Full-Bridge Motor Driver
General Description
The LMD18245 full-bridge power amplifier incorporates all
the circuit blocks required to drive and control current in a
brushed type DC motor or one phase of a bipolar stepper
motor. The multi-technology process used to build the device
combines bipolar and CMOS control and protection circuitry
with DMOS power switches on the same monolithic struc-
ture. The LMD18245 controls the motor current via a fixed
off-time chopper technique.
An all DMOS H-bridge power stage delivers continuous out-
put currents up to 3A (6A peak) at supply voltages up to 55V.
The DMOS power switches feature low RDS(ON) for high ef-
ficiency, and a diode intrinsic to the DMOS body structure
eliminates the discrete diodes typically required to clamp bi-
polar power stages.
An innovative current sensing method eliminates the power
loss associated with a sense resistor in series with the motor.
A four-bit digital-to-analog converter (DAC) provides a digital
path for controlling the motor current, and, by extension, sim-
plifies implementation of full, half and microstep stepper mo-
tor drives. For higher resolution applications, an external
DAC can be used.
Features
n DMOS power stage rated at 55V and 3A continuous
n Low RDS(ON) of typically 0.3Ω per power switch
n Internal clamp diodes
n Low-loss current sensing method
n Digital or analog control of motor current
n TTL and CMOS compatible inputs
n Thermal shutdown (outputs off) at TJ = 155˚C
n Overcurrent protection
n No shoot-through currents
n 15-lead TO-220 molded power package
Applications
n Full, half and microstep stepper motor drives
n Stepper motor and brushed DC motor servo drives
n Automated factory, medical and office equipment
Functional Block and Connection Diagram (15-Lead TO-220 Molded Power Package (T) )
Order Number LMD18245T
See NS Package Number TA15A
© 1998 National Semiconductor Corporation DS011878
DS011878-1
www.national.com
1 page  
Connection Diagram
DS011878-2
Top View
15-Lead TO-220 Molded Power Package
Order Number LMD18245T
See NS Package Number TA15A
Pinout Descriptions (See Functional Block
and Connection Diagrams)
Pin 1, OUT 1: Output node of the first half H-bridge.
Pin 2, COMP OUT: Output of the comparator. If the voltage
at CS OUT exceeds that provided by the DAC, the compara-
tor triggers the monostable.
Pin 3, RC: Monostable timing node. A parallel resistorca-
pacitor network connected between this node and ground
sets the monostable timing pulse at about 1.1 RC seconds.
Pin 5, PGND: Ground return node of the power bridge. Bond
wires (internaI) connect PGND to the tab of the TO-220
package.
Pins 4 and 6 through 8, M4 through M1: Digital inputs of
the DAC. These inputs make up a four-bit binary number
with M4 as the most significant bit or MSB. The DAC pro-
vides an analog voltage directly proportional to the binary
number applied at M4 through M1.
Pin 9, VCC: Power supply node.
Pin 10, BRAKE: Brake logic input. Pulling the BRAKE input
logic-high activates both sourcing switches of the power
bridge — effectively shorting the load. See Table 1. Shorting
the load in this manner forces the load current to recirculate
and decay to zero.
Pin 11, DIRECTION: Direction logic input. The logic level at
this input dictates the direction of current flow in the load.
See Table 1.
Pin 12, SGND: Ground return node of all signal level circuits.
Pin 13, CS OUT: Output of the current sense amplifier. The
current sense amplifier sources 250 µA (typical) per ampere
of total forward current conducted by the upper two switches
of the power bridge.
Pin 14, DAC REF: Voltage reference input of the DAC. The
DAC provides an analog voltage equal to VDAC REF x D/16,
where D is the decimal equivalent (0–15) of the binary num-
ber applied at M4 through M1.
Pin 15, OUT 2: Output node of the second half H-bridge.
TABLE 1. Switch Control Logic Truth Table
BRAKE DIRECTION MONO
H XX
L HL
L HH
L LL
L LH
X = don’t care
MONO is the output of the monostable.
Active Switches
Source 1, Source 2
Source 2
Source 2, Sink 1
Source 1
Source 1, Sink 2
Functional Descriptions
TYPICAL OPERATION OF A CHOPPER AMPLIFIER
Chopper amplifiers employ feedback driven switching of a
power bridge to control and limit current in the winding of a
motor (Figure 1). The bridge consists of four solid state
power switches and four diodes connected in an H configu-
ration. Control circuitry (not shown) monitors the winding
current and compares it to a threshold. While the winding
current remains less than the threshold, a source switch and
a sink switch in opposite halves of the bridge force the sup-
ply voltage across the winding, and the winding current in-
creases rapidly towards VCC/R (Figure 1a and Figure 1d ).
As the winding current surpasses the threshold, the control
circuitry turns OFF the sink switch for a fixed period or
off-time. During the off-time, the source switch and the oppo-
site upper diode short the winding, and the winding current
recirculates and decays slowly towards zero (Figure 1b and
Figure 1e ). At the end of the off-time, the control circuitry
turns back ON the sink switch, and the winding current again
increases rapidly towards VCC/R (Figure 1a and Figure 1d
again). The above sequence repeats to provide a current
chopping action that limits the winding current to the thresh-
old (Figure 1g ). Chopping only occurs if the winding current
reaches the threshold. During a change in the direction of
the winding current, the diodes provide a decay path for the
initial winding current (Figure 1c and Figure 1f ). Since the
bridge shorts the winding for a fixed period, this type of chop-
per amplifier is commonly referred to as a fixed off-time
chopper.
5 www.national.com
5 Page 
The Typical Application (Continued)
Top Trace: Phase A Winding Current at 1A/div
Bottom Trace: Phase B Winding Current at 1A/div
Horizontal: 1 ms/div
*500 steps/second
DS011878-17
DS011878-18
BRAKE A = BRAKE B = 0
FIGURE 7. Winding Currents and Digital Control Signals for One-Phase-On Drive (Wave Drive)
11 www.national.com
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LMD18245T.PDF ] | |
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