LM2650

SNVS133C – JUNE 1999 – REVISED APRIL 2013

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Table 2. Toroidal Inductors Using Cores from MICROMETALS, INC.

Core Number

Core Material

Wire Gauge

Number of Strands

Number of Turns

15

μH

T38

−52

AWG # 23

1

21

20

μH

T38

−52

AWG # 23

1

25

33

μH

T50

−52

AWG # 21

1

41

40

μH

T50 (B)

−18

AWG # 21

1

41

Table 3. Components for Typical 200 kHz Applications

Input Voltage

7V to 18V IN

Applicable Cell Stacks

8 to 12 Cell NiCd or NiMh, 3 to 4 Cell Li Ion, 8 to 11 Cell Alkaline, 6 Cell Lead Acid

Output

5V, 3A Out

3.3V, 3A out

Input Capacitor CIN

2 x 22

μF, 35V AVX TPS

2 x 22

μF, 35V AVX TPS

Series or Sprague 593D Series

Series or Sprague 593D Series

Inductor L1

20

μH (See Table 2)

15

μH (See Table 2)

Output Capacitor COUT

3x220

μF, 10V AVX TPS

3x220

μF, 10V AVX TPS

Series or Sprague 593D Series

Series or Sprague 593D Series

Feedback Resistors R1 and R2

R1 = 75k

Ω, 1%,

R1 = 41.2k

Ω, 1%,

R2 = 24.9k

Ω, 1%,

R2 = 24.9k

Ω, 1%,

Compensation Components RC, CC,

RC = 53.6 kΩ, CC = 2.7 nF,

RC = 33.2 kΩ, CC = 3.9 nF,

R3, and C10

R3 = 4.02 kΩ, C10 = 4.7 nF

R3 = 3.01 kΩ, C10 = 6.8 nF

Sleep Resistors RSIA and RSOA

RSIA = 33 kΩ, RSOA = 200 kΩ

RSIA = 47 kΩ, RSOA = 91 kΩ

Frequency Adjusting Resistor RFA

RFA = 24.9 kΩ

RFA = 24.9 kΩ

Figure 19. An Efficient, 2% Accurate 5V to 3.3V Converter

12

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