LM3150MH/NOPB National Semiconductor, LM3150MH/NOPB Datasheet - Page 14

• Manufacturer Part Number: LM3150MH/NOPB
• Description: IC REG SWITCH CTRL 6-42V 14TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®, SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM3150MH/NOPB

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: Adj to 0.6V
• Current - Output: 12A
• Frequency - Switching: 1MHz
• Voltage - Input: 6 ~ 42 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-TSSOP Exposed Pad, 14-eTSSOP 14-HTSSOP
• Package: 14TSSOP EP
• Output Voltage: 0.6(Min) V
• Output Current: 12(Max) A
• For Use With: 551600142-002 - WEBENCH BUILD IT BOARD LM3150
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LM3150MH

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EN bypass capacitor, C
when driving the EN pin from open drain type of signal.
Design Example
1. Define Power Supply Operating Conditions
a. V
b. V
c. Typical Load Current = 12A, Max Load Current = 15A
d. Soft-Start time t
2. Set Output Voltage with Feedback Resistors
R
3. Determine R
t
At the maximum switching frequency of 687 kHz, which is
limited by the minimum on-time, the off-time of 654 ns is less
than 725 ns. Therefore the switching frequency should be re-
duced and meet the following criteria:
OFF
FB2
OUT
IN-MIN
should meet the following criteria:
= 22.6 kΩ, nearest 1% standard value.
= 3.3V
= 6V, V
t
f
OFF
smax
ON
IN-TYP
D
SS
D
= (1-0.55)/687 kHz = 654 ns
t
and f
OFF
= 0.137/ 200 ns = 687 kHz
min
max
D
D
= 5 ms
R
min
max
= 3.3V/24V = 0.137
FB2
> t
= 12V, V
t
= 3.3V / 6V = 0.55
EN
OFF
S
= V
OFF-MIN
= V
, recommended value is 1000 pF
= 22.455 kΩ
> 725 ns
OUT
OUT
IN-MAX
/V
/V
+ 200 ns
IN-MAX
IN-MIN
= 24V
FIGURE 5. Design Example Schematic
14
A switching frequency is arbitrarily chosen at 500 kHz which
should allow for reasonable size components and satisfies
the requirements above.
f
Using f
Next, check the desired minimum input voltage for R
Figure
voltage of 6V.
4. Determine Inductor Required
a. ET = (24-3.3) x (3.3/24) x (1000/500) = 5.7 V µs
b. From the inductor nomograph a 12A load and 5.7 V µs cal-
culation corresponds to a L44 type of inductor.
c. Using the inductor designator L44 in
HA3778–AL 1.65 µH inductor is chosen.
5. Determine Output Capacitance
The voltage rating on the output capacitor should be greater
than or equal to the output voltage. As a rule of thumb most
capacitor manufacturers suggests not to exceed 90% of the
capacitor rated voltage. In the case of multilayer ceramics the
capacitance will tend to decrease dramatically as the applied
voltage is increased towards the capacitor rated voltage. The
S
R
= 500 kHz
ON
R
= [(3.3 x 12) - 3.3] / (12 x 100 pC x 500 kHz) - 4.3 kΩ
S
ON
R
2. This design will meet the desired minimum input
R
= 500 kHz R
OND
OND
= [(V
= - [(V
f
= - [(12 - 1) x (12 x 16.5 + 100)] -1000
S
OUT
< (1 - 0.55)/725 ns = 620 kHz
x V
IN
f
ON
- 1) x (V
s
IN
R
R
< (1 - D)/725 ns
) - V
OND
can be calculated as follows:
ON
= 56.2 kΩ
OUT
= -4.3 kΩ
IN
] / (V
x 16.5 + 100)] - 1000
IN
x K x f
Table 1
30053161
S
) + R
the Coilcraft
OND
ON
using