LT8302 datasheet(11/20 Pages) LINER

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LTM8068

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For more information www.linear.com/LTM8068

APPLICATIONS INFORMATION

For most applications, the design process is straight for-

ward, summarized as follows:

1. Look at Table 1a (or Table 1b, if the post linear regula-

tor is used) and find the row that has the desired input

range and output voltage.

2. Apply the recommended CIN, COUT1, COUT2, RFB1 and

RFB2 as required.

While these component combinations have been tested

for proper operation, it is incumbent upon the user to

verify proper operation over the intended system’s line,

load and environmental conditions. Bear in mind that

the maximum output current may be limited by junc-

tion temperature, the relationship between the input and

output voltage magnitude and polarity and other factors.

Please refer to the graphs in the Typical Performance

Characteristics section for guidance.

Capacitor Selection Considerations

The CIN, COUT1 and COUT2 capacitor values in Table 1 are

the minimum recommended values for the associated

operating conditions. Applying capacitor values below

those indicated in Table 1 is not recommended, and may

result in undesirable operation. Using larger values is

generally acceptable, and can yield improved dynamic

response, if it is necessary. Again, it is incumbent upon

the user to verify proper operation over the intended sys-

tem’s line, load and environmental conditions.

Ceramic capacitors are small, robust and have very low

ESR. However, not all ceramic capacitors are suitable. X5R

and X7R types are stable over temperature and applied

voltage and give dependable service. Other types, includ-

ing Y5V and Z5U have very large temperature and voltage

coefficients of capacitance. In an application circuit they

may have only a small fraction of their nominal capaci-

tance resulting in much higher output voltage ripple than

expected.

A final precaution regarding ceramic capacitors concerns

the maximum input voltage rating of the LTM8068. A

ceramic input capacitor combined with trace or cable

inductance forms a high-Q (underdamped) tank circuit.

If the LTM8068 circuit is plugged into a live supply, the

input voltage can ring to much higher than its nominal

value, possibly exceeding the device’s rating. This situa-

tion is easily avoided; see the Hot-Plugging Safely section.

LTM8068 Table 1a. Recommended Component Values and Configuration for Specific VOUT1 Voltages (TA = 25°C)

VIN

VOUT1

CIN

COUT1

RFB1

2.8V to 40V

2.5V

2.2µF, 50V, 1206

100µF, 6.3V, 1210

15.4k

2.8V to 40V

3.3V

2.2µF, 50V, 1206

47µF, 6.3V, 1210

11.8k

2.8V to 40V

2.2µF, 50V, 1206

22µF, 16V, 1210

8.25k

2.8V to 37V

2.2µF, 50V, 1206

22µF, 16V, 1210

5.23k

2.8V to 33V

12V

4.7µF, 50V, 1206

10µF, 50V, 1210

3.48k

2.8V to 30V

15V

4.7µF, 50V, 1206

4.7µF, 25V, 1210

2.8k

2.8V to 27V

18V

4.7µF, 50V, 1206

4.7µF, 25V, 1210

2.37k

Note: An input bulk capacitor is required.

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