AN-2084 Datasheet, PDF (1/10 Pages) National Semiconductor (TI) – LMZ1420xEXT/ LMZ1200xEXT Evaluation Board

LMZ1420xEXT /
LMZ1200xEXT Evaluation
Board
National Semiconductor
Application Note 2084
Alan Martin
August 16, 2010
Introduction
The LMZ1420xEXT and LMZ1200xEXT SIMPLE SWITCH-
ER® power modules are easy-to-use DC-DC solution capa-
ble of driving up to a 3A load with exceptional power
conversion efficiency, output voltage accuracy, line and load
regulation. They are available in an innovative package that
enhances thermal performance and allows for hand or ma-
chine soldering.
The LMZ14203EXT/2EXT/1EXT can accept an input voltage
rail between 6V and 42V and the LMZ12003EXT/2EXT/1EXT
can accept an input voltage rail between 4.5V and 20V. The
devices can deliver an adjustable and highly accurate output
voltage as low as 0.8V and as high as 6V. The control struc-
ture is constant on-time with input voltage feed forward. This
creates a nearly constant switching frequency across the in-
put voltage range. The control loop operates well with low
ESR output capacitors such as ceramics. An output feed-for-
ward capacitor across the upper feedback resistor trims for
optimum transient response. The precision enable input al-
lows for programmable UVLO of the input supply. The exter-
nal soft-start capacitor facilitates controlled startup output rise
time. The LMZ1420xEXT and LMZ1200xEXT family is a reli-
able and robust solution with the following features: lossless
cycle-by-cycle valley current limit to protect for over current
or short-circuit fault, thermal shutdown, input under-voltage
lock-out, and will start up into a pre-biased output. The
LMZ1420xEXT and LMZ1200xEXT families are shock and
vibration certified and rated for operation down to –55°C.
Board Specifications
• LMZ1420xEXT V_IN = 6V to 42V
• LMZ1420xEXT enable UVLO = 8V
• LMZ1420xEXT V_OUT = 3.3V
• LMZ1200xEXT V_IN = 4.5V to 20V
• LMZ1200xEXT enable UVLO = 4.5V
• LMZ1200xEXT V_OUT = 1.8V
• Operates at full load up to 80°C ambient at 12V input
• θ_JA = 20°C / W, θ_JC = 1.9°C / W
• Designed on four layers, all four layers are 1 oz. copper
weight
• The two internal ground planes are identical
• Measures 1.705 in. x 3.03 in. (4.33 cm x 7.7cm) and is
62mil (.062”) thick of FR4 laminate material
For additional circuit modifications refer to the Design Con-
sideration section of the LMZ1420xEXT or LMZ1200xEXT
data sheet. For negative output voltage connections see
AN-2027.
Additional Footprints
Additional component mounting pads are available to exper-
iment with alternative Cin and Cout combinations or a zener
clamp on the enable input. See Figure 6 for corresponding
schematic locations.
FIGURE 1. Evaluation Board Schematic
(LMZ1200xEXT 1.8V application values shown in parentheses)
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