LTC1753 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC1753
Linear Technology
'LTC1753' PDF : 24 Pages View PDF
LTC1753
APPLICATIO S I FOR ATIO
response using a network analyzer to find the actual loop
poles and zeros.
Table 5 shows the suggested compensation components
for 5V input applications based on the inductor and output
capacitor values. The values were calculated using mul-
tiple paralleled 330µF AVX TPS series surface mount
tantalum capacitors as the output capacitor. The optimum
component values might deviate from the suggested
values slightly because of board layout and operating
condition differences.
Table 5. Suggested Compensation Network for 5V Input
Application Using Multiple Paralleled 330µF AVX TPS Output
Capacitors
LO (µH)
1
CO (µF)
990
RC (kΩ)
1.8
CC (µF)
0.022
C1 (pF)
680
1
1980
3.6
0.01
330
1
4950
9.1
0.01
120
2.7
990
5.1
0.01
220
2.7
1980
10
0.01
120
2.7
4950
24
0.0047
47
5.6
990
10
0.01
120
5.6
1980
20
0.0047
56
5.6
4950
51
0.0033
22
An alternate output capacitor is the Sanyo MV-GX series.
Using multiple parallel 1500µF Sanyo MV-GX capacitors
for the output capacitor, Table 6 shows the suggested
compensation component value for a 5V input application
based on the inductor and output capacitor values.
Table 6. Suggested Compensation Network for 5V Input
Application Using Multiple Paralleled 1500µF Sanyo MV-GX
Output Capacitors
LO (µH)
1
CO (µF)
4500
RC (kΩ)
4.3
CC (µF)
0.022
C1 (pF)
270
1
6000
5.6
0.015
220
1
9000
8.2
0.01
150
2.7
4500
11
0.01
100
2.7
6000
15
0.01
82
2.7
9000
22
0.01
56
5.6
4500
24
0.01
56
5.6
6000
30
0.0047
39
5.6
9000
47
0.0047
27
Table 7 shows the suggested compensation component
value for a 5V application based on the Sanyo OS-CON
4SP820M low ESR output capacitors
Table 7. Suggested Compensation Network for 5V Input
Application Using Multiple Paralleled 820µF Sanyo OS-CON
4SP820M Output Capacitors
LO (µH)
1
CO (µF)
1640
RC (kΩ)
5.6
CC (µF)
0.01
C1 (pF) C2 (pF)
220
270
1
2460
9.1
0.0047
150
270
1
4100
15
0.0047
82
270
2.7
1640
16
0.0047
82
270
2.7
2460
24
0.0033
56
270
2.7
4100
39
0.0022
33
270
5.6
1640
33
0.0033
39
270
5.6
2460
47
0.0022
27
270
5.6
4100
82
0.0022
15
270
Remote Sense Considerations
In some installations such as Intel Slot 2 designs, the
regulator is by necessity a relatively long distance from the
load. It is desirable in these instances to connect the
regulator sense connection at the load rather than directly
at the regulator output. This forces the supply voltage to
be regulated at the load which, after all, is the desired point
to control. In most cases no problems will be encountered
as a result of doing this. However, care must be exercised
if the power path is long or the capacitance at the load is
very large.
The power distribution path has some finite amount of
inductance. There will also be a significant amount of
capacitance at the load as the local bypass. These two
circuit elements constitute a second order, lowpass filter
and the SENSE lead connects to the output of this filter. As
is true for any LC filter, there is 180° of phase shift at a
frequency beyond the double pole. If the resonant fre-
quency of the filter falls below the regulator’s feedback
loop crossover frequency, the loop will likely oscillate.
There are a couple of measures that may be taken to
alleviate this problem. The first is to minimize the induc-
tance of the power path. Therefore, it is desirable to make
the power trace as wide as possible and as short as
18
Share Link: 