LTC1753CSW datasheet(18/24 Pages) LINER

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LTC1753

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 330

µF 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 330

µF AVX TPS Output

Capacitors

LO (µH)

CO (µF)

RC (kΩ)CC (µF)

C1 (pF)

990

1.8

0.022

680

1980

3.6

0.01

330

4950

9.1

0.01

120

2.7

990

5.1

0.01

220

2.7

1980

0.01

120

2.7

4950

0.0047

5.6

990

0.01

120

5.6

1980

0.0047

5.6

4950

0.0033

An alternate output capacitor is the Sanyo MV-GX series.

Using multiple parallel 1500

µF 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 1500

µF Sanyo MV-GX

Output Capacitors

LO (µH)

CO (µF)

RC (kΩ)CC (µF)

C1 (pF)

4500

4.3

0.022

270

6000

5.6

0.015

220

9000

8.2

0.01

150

2.7

4500

0.01

100

2.7

6000

0.01

2.7

9000

0.01

5.6

4500

0.01

5.6

6000

0.0047

5.6

9000

0.0047

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 820

µF Sanyo OS-CON

4SP820M Output Capacitors

LO (µH)

CO (µF)

RC (kΩ)CC (µF)

C1 (pF)

C2 (pF)

1640

5.6

0.01

220

270

2460

9.1

0.0047

150

270

4100

0.0047

270

2.7

1640

0.0047

270

2.7

2460

0.0033

270

2.7

4100

0.0022

270

5.6

1640

0.0033

270

5.6

2460

0.0022

270

5.6

4100

0.0022

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

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