LTM8046 datasheet(10/20 Pages) LINER

10 / 20 page

LTM8046

8046fb

For more information www.linear.com/LTM8046

applicaTions inForMaTion

For most applications, the design process is straight-

forward, summarized as follows:

1. Look at Table 1 and find the row that has the desired

input range and output voltage.

2. Apply the recommended CIN, COUT and RFB.

3. Connect BIAS as indicated, or tie to an external source

up to 15V or VIN, whichever is less.

Whilethesecomponentcombinationshavebeentestedfor

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 junction 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 and COUT capacitor values in Table 1 are the

minimum recommended values for the associated oper-

ating 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 system’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 ap-

plied voltage and give dependable service. Other types,

including Y5V and Z5U have very large temperature and

voltage coefficients of capacitance. In an application cir-

cuit they may have only a small fraction of their nominal

capacitance resulting in much higher output voltage ripple

than expected.

A final precaution regarding ceramic capacitors concerns

the maximum input voltage rating of the LTM8046. A

ceramic input capacitor combined with trace or cable

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

the LTM8046 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 situation is

easily avoided; see the Hot-Plugging Safely section.

Table 1. Recommended Components and Configuration (TA = 25°C)

VIN

VOUT

CIN

COUT

RFB

3.2V to 32V

1.8V

1µF, 50V, 0805 X5R

× 100µF, 6.3V, 1206 X5R

18.7k

3.2V to 31V

2.5V

1µF, 50V, 0805 X5R

× 100µF, 6.3V, 1206 X5R

14.7k

3.2V to 29V

3.3V

1µF, 50V, 0805 X5R

100µF, 6.3V, 1206 X5R

11.8k

3.2V to 26V

1µF, 25V, 0603 X5R

100µF, 6.3V, 1206 X5R

8.45k

3.2V to 20V

1µF, 25V, 0603 X5R

47µF, 10V, 1206 X5R

5.49k

3.2V to 12V

12V

1µF, 25V, 0603 X5R

× 10µF, 16V, 1210 X5R

3.83k

3.2V to 25V

2.5V

1µF, 25V, 0603 X5R

× 100µF, 6.3V, 1206 X5R

14.7k

3.2V to 25V

3.3V

1µF, 25V, 0603 X5R

100µF, 6.3V, 1206 X5R

11.8k

CBIAS = 1µF 10V 0402 X5R

BIAS = 3.3V for VIN ≥ 3.3V, VIN for VIN < 3.3V. If BIAS = VIN, the minimum input voltage is 4.3V.

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