LM2698 datasheet(9/25 Pages) TI

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L >

VIN x D x (1-D)

2 x fS x IOUT(AVG)

VIN x D

2 x fS x L

IOUT(AVG)

1-D

VL(t) L

diL(t)

t (s)

IL(AVG)

D*Ts

IL (A)

ID (A)

(a)

(b)

'iL

t (s)

ID(AVG) =

IOUT(AVG)

VIN - VOUT

VIN

LM2698

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SNVS153E – MAY 2001 – REVISED APRIL 2013

Inductor

Figure 15. (a) Inductor Current (b) Diode Current

The inductor is one of the two energy storage elements in a boost converter. Figure 15 shows how the inductor

current varies during a switching cycle. The current through an inductor is quantified as:

(2)

If VL(t) is constant, diL / dt must be constant, thus the current in the inductor changes at a constant rate. This is

the case in DC/DC converters since the voltages at the input and output can be approximated as a constant. The

current through the inductor of the LM2698 boost converter is shown in Figure 15(a). The important quantities in

determining a proper inductance value are IL(AVG) (the average inductor current) and ΔiL (the inductor current

ripple). If

ΔiL is larger than IL(AVG), the inductor current will drop to zero for a portion of the cycle and the converter

will operate in discontinuous conduction mode. If

ΔiL is smaller than IL(AVG), the inductor current will stay above

zero and the converter will operate in continuous conduction mode (CCM). All the analysis in this datasheet

assumes operation in continuous conduction mode. To operate in CCM:

IL(AVG) > ΔiL

(3)

(4)

(5)

Choose the minimum IOUT to determine the minimum L for CCM operation. A common choice is to set ΔiL to 30%

of IL(AVG).

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