LMZ10503EXTTZ Datasheet, PDF (1/12 Pages) National Semiconductor (TI) – LMZ1050xEXT Evaluation Board

LMZ1050xEXT Evaluation
Board
National Semiconductor
Application Note 2074
Yang Zhang
August 16, 2010
Introduction
The LMZ1050xEXT SIMPLE SWITCHER® power module is
a complete, easy-to-use DC-DC solution capable of driving
up to 3A, 4A, or 5A load with exceptional power conversion
efficiency, output voltage accuracy, line and load regulation.
The LMZ1050xEXT is available in an innovative package that
enhances thermal performance and allows for hand or ma-
chine soldering.
The LMZ1050xEXT can accept an input voltage rail between
2.95V and 5.5V and deliver an adjustable and highly accurate
output voltage as low as 0.8V. One megahertz fixed frequen-
cy PWM switching provides a predictable EMI characteristic.
Two external compensation components can be adjusted to
set the fastest response time, while allowing the option to use
ceramic and/or electrolytic output capacitors. Externally pro-
grammable soft-start capacitor facilitates controlled startup.
The LMZ1050xEXT is a reliable and robust solution with the
following features: lossless cycle-by-cycle peak current limit
to protect for over current or short-circuit fault, thermal shut-
down, input under-voltage lock-out, and pre-biased startup.
Board Specifications
• V_IN = 2.95V to 5.5V
• V_OUT = 2.5V (default output voltage setting, refer to Table
2 for other output settings)
• ±2.5% feedback voltage accuracy at 2.5V output
(Including line and load regulation from T_J = -55°C to
125°C)
• ±1.63% feedback voltage accuracy over temperature
• I_OUT = 0A to 3A, 4A, and 5A
• θ_JA = 20°C/W, θ_JC = 1.9°C/W
• Designed on four layers, the top and bottom layers are
1oz. copper and the two inner layers are 1/2 oz. copper
weight
• Measures 2.25 in. x 2.25 in. (5.8 cm x 5.8 cm) and is 62mil
(.062”) thick on a FR4 laminate
Evaluation Board Design Concept
The evaluation board is designed to demonstrate low con-
ducted noise on the input and output lines, as seen in Figure
11 and Figure 14. Four input capacitors (C_in1 - C _in4) and three
output capacitors (C_o1 - C_o3) are populated for this purpose.
All the input and output filter capacitors are not necessary to
comply with radiation standards. For a circuit example that
passes radiated emissions standards (EN55022, class B)
please refer to Figure 19. Additionally, C_in5 is present to re-
duce the resonance of the input line produced by the induc-
tance and resistance in the cables connecting the bench
power supply to the evaluation board and the input capacitors.
Additional Component Footprints
When the tracking feature of the LMZ1050xEXT is used, re-
move the soft-start capacitor C_SS and use a resistor divider
on designators R_trkb and R_trkt. The ground and V_trk post have
been provided for easy connection.
The LMZ1050xEXT eval board incorporates a precision en-
able circuit which is pulled high by a 100 kΩ pull up resistor
to VIN. This allows the user to pull low on the enable pin to
ground. The top enable resistor is R_ent and the bottom enable
resistor is R_enb. Refer to the Design Guideline and Operating
Description section of the LMZ1050xEXT data sheet for de-
tailed design implementation.
Select FPGAs specify input inrush currents for particular pow-
er-up sequences and others require sequencing rails to avoid
start-up or latch-up problems. To prevent early turn-on of the
LMZ1050xEXT in systems with multiple power rails, precision
enable and tracking are useful as the main input voltage rail
rises at power-up.
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