SC2614MLTR Semtech, SC2614MLTR Datasheet - Page 11

• Manufacturer Part Number: SC2614MLTR
• Manufacturer: Semtech

Specifications of SC2614MLTR

• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Pin Count: 18
• Mounting: Surface Mount
• Package Type: MLP
• Case Length: 6mm
• Screening Level: Commercial
• Lead Free Status / Rohs Status: Not Compliant

to correct the output filter corner frequency and the ESR
zero frequency. In some cases, the filter inductance may
also need to be adjusted to shift the filter corner
frequency. It is not recommended to use only high fre-
quency multi-layer ceramic capacitors for output filter.
(4) Choose the loop gain cross over frequency (0 dB fre-
quency). It is recommended that the crossover frequency
is always less than one fifth of the switching frequency :
If the transient specification is not stringent, it is better
to choose a crossover frequency that is less than one
tenth of the switching frequency for good noise immunity.
The resistor in the compensation network can then be
calculated as:
when
or
when
(5) The compensation capacitor is determined by choos-
ing the compensator zero to be about one fifth of the
output filter corner frequency:
(6) The final step is to generate the Bode plot, either by
using the simulation model in Fig. 1 or using the equa-
tions provided here with Mathcad. The phase margin
can then be checked using the Bode plot. Usually, this
design procedure ensures a healthy phase margin.
An example is given below to demonstrate the proce-
dure introduced above. The parameters of the power
supply are given as:
POWER MANAGEMENT
Applications Information (Cont.)
© 2004 Semtech Corp.
R
R
:=
:=
G
G
pwm
pwm
⋅
1
V
⋅
1
V
F
in
F
F zero
C
in
⋅
o
G
esr
⋅
F
<
G
m
x_over
F
<
m
⋅
⎛
⎜
⎝
esr
F
⋅
2 π . R
⎛
⎜
⎝
F
F
o
F
<
esr
F
o
<
≤
esr
.
F
o
F
⎞
⎠
F
F o
x_over
2
x_over
⎞
⎠
5
1
.
5
sw
⋅
F zero
2
⎛
⎜
⎝
⋅
⎛
⎜
⎝
F
F
x_over
F
F
x_over
o
esr
⎞
⎠
⋅
⎞
⎠
⎛
⎜
⎝
⋅
⎛
⎜
⎝
V
V
V
V
bg
o
bg
o
⎞
⎠
⎞
⎠
11
Step 1. Output filter corner frequency
Step 2. ESR zero frequency:
Step 3. Check the following condition:
Which is satisfied in this case.
Step 4. Choose crossover frequency and calculate
compensator R:
Step 5. Calculate the compensator C:
Step 6. Generate Bode plot and check the phase margin.
In this case, the phase margin is about 85°C that en-
sures the loop stability. Fig. 2 shows the Bode plot of the
loop.
F
R = 43.197 KΩ
F
F
C = 16.287 nF
C
F
esr
R
R
R
x_over
F
sw
o
V
V
o
I
c
= 4.019 KHz
esr
L := 3
1
2
= 1.13 KHz
o
o
:= 6600
:= 0.006
in
:= 250 KHz
:= 1.0 K
:= 1.0 K
<
= 50 KHz
:= 2.5 V
:= 20 A
:= 5 V
F
µ
5
sw
H
µ
Ω
Ω
Ω
F
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