LM5085EVAL National Semiconductor, LM5085EVAL Datasheet - Page 4

• Manufacturer Part Number: LM5085EVAL
• Description: BOARD EVALUATION FOR LM5085
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5085EVAL

• Design Resources: LM(2)5085 Quick Start Calculator
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 5V
• Current - Output: 4.5A
• Voltage - Input: 5.5 ~ 55V
• Regulator Topology: Buck
• Frequency - Switching: 300kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5085
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

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B) Reduced Ripple Level Configuration: This configuration
generates more ripple at V
but uses one less capacitor. If some ripple is acceptable in
the application, this configuration is slightly more economical,
and simpler. R6 and C5 are used instead of R7, C9 and C10,
as shown in Figure 5.
Ripple is generated at V
flows through R6, and that ripple voltage is passed to the FB
pin via C5. The ripple at V
p since it is not attenuated by R1 and R2. The minimum value
for R6 is calculated from:
OUT
OUT
OUT
as the inductor’s ripple current
can be set as low as 25 mVp-
than the above configuration,
FIGURE 4. Minimum Ripple Using R7, C9, C10
FIGURE 5. Reduced Ripple Configuration
4
where I
occurs at minimum input voltage, and is 116 mAp-p at 5.5V.
The minimum value for R6 calculates to 0.22 ohms. Using a
standard value 0.27Ω resistor for R6, the ripple at V
ranges from 31 mVp-p to 321 mVp-p over the input voltage
range. See Figure 11.
The minimum value for C5 is determined from:
Where t
uation board. The minimum value for C5 calculates to 4113
pF.
OR(min)
ON(max)
is the minimum inductor’s ripple current, which
is the maximum on-time, 3479 ns in this eval-
30072011
30072012
OUT