lm4570lqx National Semiconductor Corporation, lm4570lqx Datasheet - Page 9

• Manufacturer Part Number: lm4570lqx
• Description: Single-ended Input Motor Driver
• Manufacturer: National Semiconductor Corporation

Application Information
GAIN SETTING
The resistors R
by:
Where A
ended gain by a factor of 2. This doubling is due to the
differential output architecture of the LM4570. Driving the
load differentially doubles the output voltage compared to a
single-ended output amplifier under the same conditions.
POWER DISSIPATION
The Power Dissipation vs. Supply Voltage graph in the Op-
erating Curves section shows the power dissipation of the
EXPOSED-DAP MOUNTING CONSIDERATIONS
The LM4570 is available in an 8-pin LLP package which
features an exposed DAP (die attach paddle). The exposed
DAP provides a direct thermal conduction path between the
die and the PCB, improving the thermal performance by
reducing the thermal resistance of the package. Connect the
exposed DAP to GND through a large pad beneath the
device, and multiple vias to a large unbroken GND plane.
For best thermal performance, connect the DAP pad to a
GND plane on an outside layer of the PCB. Connecting the
DAP to a plane on an inner layer will result in a higher
thermal resistance. Ensure efficient thermal conductivity by
plugging and tenting the vias with plating and solder mask,
respectively.
POWER SUPPLY BYPASSING
Good power supply bypassing is critical for proper operation.
Locate both the REF1 and V
VD
is the differential gain. A
IN
and R
V
VD
F
= 2 x (R
set the gain of the LM4570, given
DD
bypass capacitors as close
F
/ R
VD
IN
FIGURE 3. Power Dissipation vs. Input Voltage
)
differs from single-
(Continued)
9
LM4570 with the input equal to the supply voltage, meaning
the outputs swing rail-to-rail. This configuration results in the
output devices of the LM4570 operating in the linear region,
essentially very small resistors determined by the R
the output devices. Under these conditions, the power dissi-
pation is dominated by the I*R drop associated with the
output current across the R
thus the power dissipation is very low (60mW for a 800mW
output).
When the input voltage is not equal to GND or V
power dissipation of the LM4570 increases (Figure 3). Under
these conditions, the output devices operate in the satura-
tion region, where the devices consume current in addition to
the current being steered to the load, increasing the power
dissipation. Power dissipation for typical motor driving appli-
cations should not be an issue since the most of the time the
device outputs will be driven rail-to-rail.
to the device as possible. Typical applications employ a
regulator with a 10µF tantalum or electrolytic capacitor and a
ceramic bypass capacitor which aid in supply stability. This
does not eliminate the need for bypass capacitors near the
LM4570. Place a 1µF ceramic capacitor as close to V
possible. Place a 0.1µF capacitor as close to REF1 as
possible. Smaller values of C
creased turn on times.
SHUTDOWN FUNCTION
The LM4570 features a low power shutdown mode that
disables the device and reduces quiescent current con-
sumption to 0.1µA. Driving /SD Low disables the amplifiers
and bias circuitry, and drives V
Connect /SD to V
20186328
DD
for normal operation.
DS(ON)
REF1
REF1
of the output transistors,
and the outputs to GND.
may be chosen for de-
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DS(ON)
DD
DD
, the
as
of