Data Sheet

LT83201

analog.com

Rev. A 26 of 45

where ΔIL Is the inductor ripple current as calculated in Equation 7 and ILOAD(MAX) is the maximum output load for a

given application.

As a quick example, an application requiring 3A output should use an inductor with an RMS rating of greater than 3A

and an ISAT of greater than 4A. During long-duration overload or short-circuit conditions, the inductor RMS rating

requirement is greater to avoid overheating the inductor. To keep the efficiency high, the series resistance (DCR)

should be less than 0.15Ω, and the core material should be intended for high-frequency applications.

The LT83201 limits the peak switch current to protect the switches and the system from overload faults.

The top switch current limit (IPEAK-LIMIT) is 2.9A at low duty cycles and decreases linearly to 1.6A at duty cycle = 80%.

The inductor value must be sufficient to supply the desired maximum output current (IOUT(MAX)), which is a function

of the top switch current limit (IPEAK-LIMIT) and the ripple current (see Equation 6).

IOUT(MAX) = IPEAK−LIMIT −

∆IL

2

(6)

The peak-to-peak ripple current in the inductor can be calculated using Equation 7.

∆IL =

VOUT

L × fSW

× (1 −

VOUT

VIN(MAX)

)

(7)

where fSW is the switching frequency of the LT83201, and L is the value of the inductor. Therefore, the maximum

output current that the LT83201 deliver depends on the switch current limit, the inductor value, and the input and

output voltages. The inductor value may have to be increased if the inductor ripple current does not allow sufficient

maximum output current (IOUT(MAX)) given the switching frequency and maximum input voltage used in the desired

application.

The optimum inductor for a given application may differ from the one indicated by this design guide. A larger-value

inductor provides a higher maximum load current and reduces the output voltage ripple. For applications requiring

smaller load currents, the value of the inductor may be lower, and the LT83201 may operate with a higher ripple

current. This allows the use of a physically smaller inductor or one with a lower DCR, resulting in higher efficiency.

For more information about maximum output current and discontinuous operation, refer to the Application Note 44:

LT1074/LT1076 Design Manual.

For duty cycles greater than 50% (VOUT/VIN > 0.5), aminimum inductance is required to avoid sub-harmonic oscillation.

For more information, refer to the Application Note 19: LT1070 Design Manual. Equation 8 calculates that minimum

inductance.

LMIN =

VIN(2 × DC−1)

1 × fSW

(8)

where DC is the duty cycle ratio (VOUT/VIN), and fSW is the switching frequency.