OBSOLETE

LM2575EP, LM2575HVEP

SNVS301B – DECEMBER 2004 – REVISED APRIL 2013

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(For Continuous Mode Operation)

PROCEDURE (Adjustable Output Voltage Versions)

EXAMPLE (Adjustable Output Voltage Versions)

Given:

Given:

F = Switching Frequency (Fixed at 52 kHz)

F = 52 kHz

1. Programming Output Voltage (Selecting R1 and R2, as shown 1.Programming Output Voltage (Selecting R1 and R2)

in Figure 25 )

Use the following formula to select the appropriate resistor values.

(1)

(3)

R2 = 1k (8.13

− 1) = 7.13k, closest 1% value is 7.15k

stability with time, use 1% metal film resistors)

(2)

2. Inductor Selection (L1)

2. Inductor Selection (L1)

A. Calculate the inductor Volt • microsecond constant,

A. Calculate E • T (V •

μs)

E • T (V •

μs), from the following formula:

(5)

B. Use the E • T value from the previous formula and match it with C. I

the E • T number on the vertical axis of the Inductor Value

D. Inductance Region = H470

Selection Guide shown in Figure 30.

E. Inductor Value = 470

μH Choose fromAIEpart #430-0634,Pulse

C. On the horizontal axis, select the maximum load current.

Engineeringpart #PE-53118, or Renco part #RL-1961.

D. Identify the inductance region intersected by the E • T value and

the maximum load current value, and note the inductor code for that

region.

E. Identify the inductor value from the inductor code, and select an

appropriate inductor from the table shown in Table 2. Part numbers

are listed for three inductor manufacturers. The inductor chosen

must be rated for operation at the LM2575EP switching frequency

inductor

information,

see

the

INDUCTOR

SELECTION

in

APPLICATION HINTS.

A. The value of the output capacitor together with the inductor A.

defines the dominate pole-pair of the switching regulator loop. For

stable

operation,

the

capacitor

must

satisfy

the

following

(7)

requirement:

However, for acceptable output ripple voltage select

(6)

The above formula yields capacitor values between 10

μF and 2000

μF that will satisfy the loop requirements for stable operation. But to

achieve an acceptable output ripple voltage, (approximately 1% of

the output voltage) and transient response, the output capacitor may

need to be several times larger than the above formula yields.

B. The capacitor's voltage rating should be at last 1.5 times greater

than the output voltage. For a 10V regulator, a rating of at least 15V

or more is recommended.

Higher voltage electrolytic capacitors generally have lower ESR

numbers, and for this reason it may be necessary to select a

capacitor rate for a higher voltage than would normally be needed.

16

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