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User's Guide
SNVA421D–January 2010–Revised April 2013
AN-2022 LMZ1050x Evaluation Board
1 Introduction
The LMZ1050x 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 frequency 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
programmable soft-start capacitor facilitates controlled startup. The LMZ1050x 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 shutdown, input under-voltage lock-out, and pre-biased startup.
2 Board Specifications
• V
IN
= 2.95V to 5.5V
• V
OUT
= 2.5V (default output voltage setting; for other output settings, see Table 2)
• ±2.5% feedback voltage accuracy at 2.5V output (Including line and load regulation from T
J
= -40°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
3 Evaluation Board Design Concept
The evaluation board is designed to demonstrate low conducted 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),
see Figure 19. Additionally, C
in5
is present to reduce the resonance of the input line produced by the
inductance and resistance in the cables connecting the bench power supply to the evaluation board and
the input capacitors.
4 Additional Component Footprints
When the tracking feature of the LMZ1050x is used, remove 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 LMZ1050x eval board incorporates a precision enable 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
. For detailed design implementation, see the Design Guideline and
Operating Description section of the LMZ1050x data sheet.
Select FPGAs specify input inrush currents for particular power-up sequences and others require
sequencing rails to avoid start-up or latch-up problems. To prevent early turn-on of the LMZ1050x 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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SNVA421D–January 2010–Revised April 2013 AN-2022 LMZ1050x Evaluation Board
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