LTM4643 datasheet(23/43 Pages) AD

23 / 43 page

Data Sheet

LTM8060F

analog.com

Rev. 0

23 of 43

APPLICATIONS INFORMATION

For most applications, the design process is straightforward, and summarized as follows.

1. See Table 6 and find the row with the desired input range and output voltage.

2. Apply the recommended CIN, COUT, RFB, and RT values.

3. Connect BIAS as indicated.

When using the LTM8060F with different output voltages, the higher frequency recommended by Table 6 will

usually result in the best operation. 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 is limited by the junction temperature, the relationship

between the input and output voltage magnitude as well as other factors. See the graphs in the Typical

Performance Characteristics section for guidance.

The maximum frequency (and attendant RT value) at which the LTM8060F should be allowed to switch is given in

Table 6 in the Maximum fSW column, while the recommended frequency (and RT value) for optimal efficiency over

the given input condition is given in the fSW column. There are additional conditions that must be satisfied if the

synchronization function is used. See the Synchronization section for details.

Set Output Voltage

The output voltage is programmed with a FB resistor, as shown in Figure 53. Choose the resistor value according to

Equation 1.

�� =

249��Ω

��

0.8��

− 1

(1)

A 1% resistor is recommended to maintain output voltage accuracy.

Figure 53. Set Output Voltage with a FB Resistor

Capacitor Selection Considerations

The CIN and COUT capacitor values in Table 6 are the minimum recommended values for the associated operating

conditions. Applying capacitor values below those indicated in Table 6 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.

The ceramic capacitors are small, robust, and have very low ESR. However, not all ceramic capacitors are suitable.

The X5R and X7R types are stable over temperature and applied voltage and give dependable service. Other types,

249kΩ

10pF

0.1µF

1.5µH

RFB

CURRENT MODE

CONTROLLER

0.8V

VOUT

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