VIN - VOUT

L

=

2iL

DTS

t

L

i



OUT

I

S

T

S

DT

L

VOUT

L

- VOUT

VIN

D =

VOUT + VD

VIN + VD - VSW

D =

VOUT

VIN

LM2830, LM2830-Q1

www.ti.com

SNVS454E – AUGUST 2006 – REVISED DECEMBER 2014

Typical Applications (continued)

Table 1. Bill of Materials (continued)

PART ID

PART VALUE

MANUFACTURER

PART NUMBER

L1

3.3 µH, 1.3 A

Coilcraft

ME3220-332

R2

15.0 k

Ω, 1%

Vishay

CRCW08051502F

R1

15.0 k

Ω, 1%

Vishay

CRCW08051502F

R3

100 k

Ω, 1%

Vishay

CRCW08051003F

8.2.1.2.1

Inductor Selection

The Duty Cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN):

(1)

The catch diode (D1) forward voltage drop and the voltage drop across the internal PMOS must be included to

calculate a more accurate duty cycle. Calculate D by using the following formula:

(2)

VSW can be approximated by:

VSW = IOUT × RDSON

(3)

The diode forward drop (VD) can range from 0.3 V to 0.7 V depending on the quality of the diode. The lower the

VD, the higher the operating efficiency of the converter. The inductor value determines the output ripple current.

Lower inductor values decrease the size of the inductor, but increase the output ripple current. An increase in the

inductor value will decrease the output ripple current.

One must ensure that the minimum current limit (1.2 A) is not exceeded, so the peak current in the inductor must

be calculated. The peak current (ILPK) in the inductor is calculated by:

ILPK = IOUT + ΔiL

(4)

Figure 20. Inductor Current

(5)

In general,

ΔiL = 0.1 × (IOUT) → 0.2 × (IOUT)

(6)

If

ΔiL = 20% of 1 A, the peak current in the inductor will be 1.2 A. The minimum ensured current limit over all

operating conditions is 1.2 A. One can either reduce

ΔiL, or make the engineering judgment that zero margin will

be safe enough. The typical current limit is 1.75 A.

Copyright © 2006–2014, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LM2830 LM2830-Q1