LM34914EVAL National Semiconductor, LM34914EVAL Datasheet - Page 3

• Manufacturer Part Number: LM34914EVAL
• Description: BOARD EVALUATION LM34914
• Manufacturer: National Semiconductor

Specifications of LM34914EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 5V
• Current - Output: 1A
• Voltage - Input: 8 ~ 40V
• Regulator Topology: Buck
• Frequency - Switching: 275kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM34914
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

R3 is chosen to generate 25-30 mVp-p at V
the minimum ripple current is 85 mAp-p at minimum V
couples that ripple to the FB pin without the attenuation of the
feedback resistors. C12’s minimum value is calculated from:
where t
R1//R2 is the equivalent parallel value of the feedback resis-
tors. For this evaluation board t
Minimum Load Current
The LM34914 requires a minimum load current of
ensure the boost capacitor (C4) is recharged sufficiently dur-
ON(max)
is the maximum on-time (at minimum V
FIGURE 3. Intermediate Ripple Configuration Using C12 and R3
ON(max)
is approximately 2700
OUT
FIGURE 4. Lowest Cost Configuration
knowing that
≊
500 µA to
IN
IN
), and
. C12
3
ns, and R1//R2 = 2.5 kΩ, and C12 calculates to a minimum of
1080 pF. In the circuit of Figure 3 the ripple at V
from
C) Lowest Cost Configuration: This configuration is the
same as option B above, but without C12. Since
are required at the FB pin, R3 is chosen to generate
at V
is 85 mAp-p at minimum V
at V
voltage range. If the application can tolerate this ripple level,
this is the most economical solution. The circuit is shown in
Figure 4.
ing each off-time. In this evaluation board, the minimum load
current is provided by the feedback resistor (R1, R2), allowing
the board’s minimum load current V
ro.
OUT
OUT
≊
30 mVp-p to
, knowing that the minimum ripple current in this circuit
ranges from
≊
≊
63 mVp-p over the input voltage range.
60 mVp-p to
IN
. Using 0.68Ω for R3, the ripple
≊
OUT
120 mVp-p over the input
to be specified at ze-
30000308
30000306
www.national.com
≥
OUT
25 mVp-p
≥
ranges
50 mV