LM2853-1.8EVAL National Semiconductor, LM2853-1.8EVAL Datasheet - Page 10

• Manufacturer Part Number: LM2853-1.8EVAL
• Description: BOARD EVAL LM2853-1.8
• Manufacturer: National Semiconductor
• Series: PowerWise®, SIMPLE SWITCHER®r

Specifications of LM2853-1.8EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 3A
• Voltage - Input: 3 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 550kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM2853
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -

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Applications Information
SPLIT-RAIL OPERATION
The LM2853 can be powered using two separate voltages
for AVIN and PVIN. AVIN is the supply for the control logic;
PVIN is the supply for the power FETs. The output filter
SWITCH NODE PROTECTION
The LM2853 includes protection circuitry that monitors the
voltage on the switch pin. Under certain fault conditions,
switching is disabled in order to protect the switching de-
vices. One side effect of the protection circuitry may be
observed when power to the LM2853 is applied with no or
light load on the output. The output will regulate to the rated
voltage, but no switching may be observed. As soon as the
output is loaded, the LM2853 will begin normal switching
operation.
LAYOUT GUIDELINES
These are several guidelines to follow while designing the
PCB layout for an LM2853 application.
1. The input bulk capacitor, C
2. All ground connections must be tied together. Use a
LM2853 Example Circuit Schematic
Capacitance (µF)
close to the PVIN pin to keep the resistance as low as
possible between the capacitor and the pin. High current
levels will be present in this connection.
broad ground plane, for example a completely filled back
plane, to establish the lowest resistance possible be-
220
220
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IN
, should be placed very
Part Number
TABLE 3. Recommended Capacitors (Continued)
(Continued)
FIGURE 1.
10
components need to be chosen based on the value of PVIN.
For PVIN levels lower than 3.3V, use output filter component
values recommended for 3.3V. PVIN must always be equal
to or less than AVIN.
3. The sense pin connection should be made as close to
4. The switch node connections should be low resistance
5. Allow area under the chip to solder the entire exposed
Niobium Oxide
Chemistry
Tantalum
tween all ground connections.
the load as possible so that the voltage at the load is the
expected regulated value. The sense line should not run
too close to nodes with high dV/dt or dl/dt (such as the
switch node) to minimize interference.
to reduce power losses. Low resistance means the trace
between the switch pin and the inductor should be wide.
However, the area of the switch node should not be too
large since EMI increases with greater area. So connect
the inductor to the switch pin with a short, but wide trace.
Other high current connections in the application such
as PVIN and V
low resistance and EMI.
die attach pad to ground for improved thermal perfor-
mance. Lab measurements also show improved regula-
tion performance when the exposed pad is well
grounded.
OUT
assume the same trade off between
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AVX
AVX
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