LM2743MTCX/NOPB National Semiconductor, LM2743MTCX/NOPB Datasheet - Page 19

• Manufacturer Part Number: LM2743MTCX/NOPB
• Description: IC REG CTLR BUCK N-CH 14-TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Step-Down (Buck)r

Specifications of LM2743MTCX/NOPB

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 13.5 V
• Current - Output: 20A
• Frequency - Switching: 50kHz ~ 1MHz
• Voltage - Input: 1 ~ 16 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-TSSOP
• For Use With: LM2743EVAL - BOARD EVALUATION LM2743LM2743-19AEVAL - BOARD EVALUATION LM2743-19A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LM2743MTCX

In practice, a good trade off between phase margin and band-
width can be obtained by selecting the closest ±10% capac-
itor values above what are suggested for C
closest ±10% capacitor value below the suggestion for C
and the closest ±1% resistor values below the suggestions
for R
than 100Ω, it should be replaced by a short circuit. Following
this guideline, the compensation components will be:
The transfer function of the compensation block can be de-
rived by considering the compensation components as
impedance blocks Z
As with the generic equation, G
take into account the limited bandwidth of the error amplifier.
The result is:
The total control loop transfer function H is equal to the power
stage transfer function multiplied by the error amplifier trans-
fer function.
The bandwidth and phase margin can be read graphically
from Bode plots of H
C
C
C
R
R
C1
C2
C3
C1
C2
C1
= 27pF ±10%
= 820pF ±10%
= 2.7nF ±10%
= 39.2kΩ ±1%
= 2.55kΩ ±1%
, R
C2
. Note that if the suggested value for R
F
EA
and Z
H = G
are shown in
I
around an inverting op-amp:
PS
EA-ACTUAL
x H
EA
Figure
must be modified to
16.
C1
and C
C2
C2
is less
, the
C3
,
19
The bandwidth of this example circuit is 59 kHz, with a phase
margin of 60°.
EFFICIENCY CALCULATIONS
The following is a sample calculation.
A reasonable estimation of the efficiency of a switching buck
controller can be obtained by adding together the Output
Power (P
The Output Power (P
design is (1.2V x 4A) = 4.8W. The Total Power (P
an efficiency calculation to complement the design, is shown
below.
The majority of the power losses are due to low and high side
of MOSFET’s losses. The losses in any MOSFET are group
of switching (P
FET Switching Loss (P
P
FIGURE 16. Overall Loop Gain and Phase
FET
OUT
= P
) loss and the Total Power (P
SW
SW
) and conduction losses(P
P
SW
+ P
P
OUT
= P
CND
FET
SW
) for theTypical Application Circuit
SW(ON)
= 331.8 mW
= 61.38 mW + 270.42 mW
)
+ P
SW(OFF)
TOTAL
CND
).
) loss:
20095286
20095285
www.national.com
TOTAL
), with