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LMD18200 Datasheet - Page 4

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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 I This input controls
the direction of current flow between OUTPUT 1 and OUT-
PUT 2 (pins 2 and 10) and therefore the direction of rota-
tion of a motor load
Pin 4 BRAKE Input See Table I 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
ists at each output pin
Pin 5 PWM Input See Table I 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
S
Pin 7 GROUND Connection This pin is the ground return
and is internally connected to the mounting tab
Pin 8 CURRENT SENSE Output This pin provides the
sourcing current sensing output signal which is typically
377 A A
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 I Logic Truth Table
PWM
Dir
Brake
Active Output Drivers
H
H
L
Source 1 Sink 2
H
L
L
Sink 1 Source 2
L
X
L
Source 1 Source 2
H
H
H
Source 1 Source 2
H
L
H
Sink 1 Sink 2
L
X
H
NONE
Locked Anti-Phase PWM Control
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Application Information
TYPES OF PWM SIGNALS
The LMD18200 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 A 50% duty-cycle PWM signal
represents zero drive since the net value of voltage (inte-
grated over one period) delivered to the load is zero For the
LMD18200 the PWM signal drives the direction 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 The (absolute) magni-
tude signal is duty-cycle modulated and the absence of a
pulse signal (a continuous logic low level) represents zero
drive Current delivered to the load is proportional to pulse
width For the LMD18200 the DIRECTION input (pin 3) is
driven by the sign signal and the PWM input (pin 5) is driven
1 5 mA) ex-
b
by the magnitude signal
USING THE CURRENT SENSE OUTPUT
The CURRENT SENSE output (pin 8) has a sensitivity of
377 A per ampere of output current For optimal accuracy
and linearity of this signal the value of voltage generating
resistor between pin 8 and ground should be chosen to limit
the maximum voltage developed at pin 8 to 5V or less The
maximum voltage compliance is 12V
It should be noted that the recirculating currents (free
wheeling currents) are ignored by the current sense circuit-
ry Therefore only the currents in the upper sourcing out-
puts are sensed
USING THE THERMAL WARNING FLAG
The THERMAL FLAG output (pin 9) is an open collector
transistor This permits a wired OR connection of thermal
warning flag outputs from multiple LMD18200’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 serv-
ice 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 chang-
es experienced may cause troublesome voltage transients
across system stray inductance
Sign Magnitude PWM Control
TL H 10568–4
4
TL H 10568 – 5

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