Datasheet

C
in
8
I
OUT
x D x (1 - D)
f
SW
x 'V
IN
LMZ10505EXT
www.ti.com SNVS669G –JUNE 2010–REVISED OCTOBER 2013
BLOCK DIAGRAM
Design Guideline And Operating Description
Design Steps
LMZ10505EXT is fully supported by Webench® and offers the following: component selection, performance,
electrical, and thermal simulations as well as the Build-It board, for a reduced design time. On the other hand, all
external components can be calculated by following the design procedure below.
1. Determine the input voltage and output voltage. Also, make note of the ripple voltage and voltage transient
requirements.
2. Determine the necessary input and output capacitance.
3. Calculate the feedback resistor divider.
4. Select the optimized compensation component values.
5. Estimate the power dissipation and board thermal requirements.
6. Follow the PCB design guideline.
7. Learn about the LMZ10505EXT features such as enable, input UVLO, soft-start, tracking, pre-biased startup,
current limit, and thermal shutdown.
Design Example
For this example the following application parameters exist.
• V
IN
= 5V
• V
OUT
= 2.5V
• I
OUT
= 5A
• ΔV
OUT
= 20 mV
pk-pk
• ΔV
o_tran
= ±20 mV
pk-pk
Input Capacitor Selection
A 22 µF or 47 µF high quality dielectric (X5R, X7R) ceramic capacitor rated at twice the maximum input voltage
is typically sufficient. The input capacitor must be placed as close as possible to the VIN pin and GND exposed
pad to substantially eliminate the parasitic effects of any stray inductance or resistance on the PC board and
supply lines.
Neglecting capacitor equivalent series resistance (ESR), the resultant input capacitor AC ripple voltage is a
triangular waveform. The minimum input capacitance for a given peak-to-peak value (ΔV
IN
) of V
IN
is specified as
follows:
(1)
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