Datasheet

¸
¹
·
¨
©
§
V
IN(MAX)
L =
x 1 -
V
OUT
V
OUT
I
PP
x f
SW
I
PP
I
O
0
T =
1
f
SW
5.2 x 10
9
R
T
=
f
SW
- 948 = 21.66 k:
LM5119/LM5119Q
www.ti.com SNVS676F –AUGUST 2010–REVISED FEBRUARY 2013
APPLICATION INFORMATION
EXTERNAL COMPONENTS
The procedure for calculating the external components is illustrated with the following design example. Only the
values for the 5V output are calculated since the procedure is the same for the 10V output. The circuit shown in
Figure 15 is configured for the following specifications:
• CH1 output voltage, V
OUT1
= 10.0V
• CH2 output voltage, V
OUT2
= 5.0V
• CH1 maximum load current, I
OUT1
= 4A
• CH2 maximum load current, I
OUT2
= 8A
• Minimum input voltage, V
IN(MIN)
= 14V
• Maximum input voltage, V
IN(MAX)
= 55V
• Switching frequency, f
SW
= 230kHz
Some component values were chosen as a compromise between the 10V and 5V outputs to allow identical
components to be used on both outputs. This design can be reconfigured in a dual-channel interleaved
configuration with a single 10V output which requires identical power channels.
TIMING RESISTOR
R
T
sets the switching frequency of each regulator channel. Generally, higher frequency applications are smaller
but have higher losses. Operation at 230kHz was selected for this example as a reasonable compromise
between small size and high efficiency. The value of R
T
for 230kHz switching frequency can be calculated as
follows:
(7)
A standard value or 22.1kΩ was chosen for R
T
. The internal oscillator frequency is twice the switching frequency
and is about 460kHz.
OUTPUT INDUCTOR
The inductor value is determined based on the operating frequency, load current, ripple current and the input and
output voltages.
Figure 7. Inductor Current
Knowing the switching frequency, maximum ripple current (I
PP
), maximum input voltage and the nominal output
voltage (V
OUT
), the inductor value can be calculated:
(8)
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