Datasheet

22
LTC3704
3704fb
ΔV
k
k
mV
OP P()
–.
•
.
.
–. –
••
.
−
=
⎡
⎣
⎢
⎤
⎦
⎥
=
105
300
50
35
0 0016
1
8 300 100
13 7
μ
μ
This ripple voltage calculation also assumes no coupling
between the inductors, making the 13.7mV number very
conservative.
Figure 15 illustrates the same basic application shown in
Figure 1, with the added features of soft-start and
undervoltage lockout on the input supply. Figures 16
through 21 illustrate the measured performance for this
converter. The peak efficiency is 87% at a load current of
2A and the peak-to-peak output ripple is less than 10mV.
Figures 19 and 20 illustrate the load step response at 5V
and 15V input, and Figure 21, the start-up characteristics
with a resistive load.
APPLICATIO S I FOR ATIO
WUUU
The capacitor used was a TDK 47μF, 16V X5R-dielectric
ceramic (C5750X5R1C476M), mainly because of its low
ESR (2.4mΩ) and high RMS current capability.
8. The peak-to-peak output ripple is:
ΔV
D
f
V
L
ESR
fC
OP P
MAX O
O
()
–
•
––
••
−
=
⎡
⎣
⎢
⎤
⎦
⎥
1
2
1
8
As a first try, a TDK 100μF, 6.3V X5R-dielectric ceramic
capacitor was chosen (C5750X5R0J107M). This capaci-
tor has a very low 1.6mΩ of ESR. As a result, the peak-to-
peak output ripple voltage is:
Figure 18. Output Ripple Voltage and
Inductor Current for the Circuit in Figure 15
Figure 21. Soft-Start for the Circuit in Figure 15
Figure 20. Load Step Response at V
IN
= 15V
for the Circuit in Figure 15
Figure 19. Load Step Response at V
IN
= 5V
for the Circuit in Figure 15
V
IN
= 5V
I
OUT
= –2V
V
OUT
(AC)
10mV/DIV
I
L2
(DC)
1A/DIV
1μs/DIV
3704 F18
V
IN
= 5V
V
OUT
(AC)
100mV/DIV
I
OUT
(DC)
1A/DIV
250μs/DIV
3704 F19
2A
0.5A
V
IN
= 15V
V
OUT
(AC)
100mV/DIV
I
OUT
(DC)
1A/DIV
250μs/DIV
3704 F20
2A
0.5A
V
IN
= 5V
V
OUT
1V/DIV
I
OUT
1A/DIV
1ms/DIV
3704 F21
V
OUT
I
OUT