AS1310 datasheet(17/30 Pages) AMSCO

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[v1-11] 2015-Jan-28

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AS1310 − Detailed Description

Typically, the ripple due to ESR is not dominant. ESR for the

recommended capacitors (Murata GMR), ESR = 5m

Ω to 10mΩ.

For the AS1310, maximum peak current is 480mA. Ripple due

to ESR is 2.4mV to 4.8mV.

Ripple at the input propagates through the common supply

connections, and if too high in value can cause problems

elsewhere in the system. The input capacitance is an important

component to get right.

Output Capacitor Selection

The output capacitor supports the triangular current during the

OFF-time of the power switch (inductor discharge period), and

also the load current during the wait time (Region D in

Figure 17) and ON-time (Region A in Figure 17) of the power

switch.

Note(s): There is also a ripple component due to the equivalent

series resistance (ESR) of the capacitor.

Summary

User Application Defines:

VINmin, VINmax, VOUTmin, VOUTmax, ILOADmin, ILOADmax

Inductor Selection:

Select Max on-time = 0.5μs to 3μs for AS1310. Use EQ 3 to

calculate inductor value.

Use EQ 5 to determine OFF-time.

Use EQ 6 to check that power delivery matches load

requirements assume 70% conversion efficiency.

Use EQ 13 to find overall timing period value of T at min VIN and

max VOUT for maximum load conditions.

Input Capacitor Selection:

Choose a ripple value and use EQ 14 to find the value.

Output Capacitor Selection:

Determine TWAIT via EQ 6 or EQ 13, and use EQ 16 to find the

value.

(EQ17)

NOM

OUT

WAIT

LOAD

OUT

)

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