AS1310 datasheet(16/30 Pages) AMSCO

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[v1-11] 2015-Jan-28

AS1310 − Detailed Description

PREGION_B =

Total power delivered to the load is the sum of EQ 8 and EQ 9:

From EQ 3 (using nominal values) peak current is given by:

Substituting EQ 11 into EQ 10 and re-arranging:

0.9T incorporates a wait time TWAIT = 10% T

Output power in terms of regulated output voltage and load

resistance is:

Combining EQ 12 and EQ 13:

Symbol

η reflects total energy loss between input and output

and is approximately 0.8 for these calculations. Use EQ 14 to

plot duty cycle (TON/T) changes for various output loadings and

changes to VIN.

Input Capacitor Selection

The input capacitor supports the triangular current during the

ON-time of the power switch, and maintains a broadly constant

input voltage during this time. The capacitance value is

obtained from choosing a ripple voltage during the ON-time of

the power switch. Additionally, ripple voltage is generated by

the equivalent series resistance (ESR) of the capacitor. For worst

case, use maximum peak current values from the datasheet.

Using TON = 1μs, and IPEAK = 480mA, and VRIPPLE = 50mV, EQ 15

yields:

CIN = 9.6μF

Nearest preferred would be 10μF.

(EQ9)

0.5L I

()

---------------------------

(EQ10)

TOTAL

--------

OFF

-------------

0.5L I

()

---------------------------

(EQ11)

ONVIN

---------------------

(EQ12)

TOTAL

INTON

2TL

----------------------- 0.9T

()

(EQ13)

OUT

LOAD

------------------

(EQ14)

OUT

LOAD

------------------

INTON

2TL

----------------------- 0.9T

()η

(EQ15)

PEAKTON

RIPPLE

--------------------------

(EQ16)

ESR

RIPPLE

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