Datasheet

LM22671-ADJ
+
GND
+
VIN
EN
SW
BOOT
FB
GND
RT/SYNC
VIN 4.5V to 42V
C2
22 PF
C1
2.2 PF
EN
SYNC
R3
C3
10 nF
L1
39 PH
C4
22 PF
GND
R
FBT
1.54 k:
R
FBB
976:
D1
60V, 1A
VOUT 3.3V
C6
1 PF
SS
100 1k 10k 100k 1M 10M
0
5
10
15
20
25
30
35
40
COMPENSATOR GAIN (dB)
FREQUENCY (Hz)
-ADJ
-5.0
LM22671
www.ti.com SNVS589M –SEPTEMBER 2008–REVISED APRIL 2013
Figure 20. Compensator Gain
In general, hand calculations or simulations can only aid in selecting good power stage components. Good
design practice dictates that load and line transient testing should be done to verify the stability of the application.
Also, Bode plot measurements should be made to determine stability margins. Application note AN-1889
SNVA364 shows how to perform a loop transfer function measurement with only an oscilloscope and function
generator.
Application Information
TYPICAL BUCK REGULATOR APPLICATION
Figure 21 shows an example of converting an input voltage range of 5.5V to 42V, to an output of 3.3v at 500mA.
See AN-1895 (SNVA368) for more information.
Figure 21. Typical Buck Regulator Application
EXTERNAL COMPONENTS
The following guidelines should be used when designing a step-down (buck) converter with the LM22671.
INDUCTOR
The inductor value is determined based on the load current, ripple current, and the minimum and maximum input
voltages. To keep the application in continuous conduction mode (CCM), the maximum ripple current, I
RIPPLE
,
should be less than twice the minimum load current.
The general rule of keeping the inductor current peak-to-peak ripple around 30% of the nominal output current is
a good compromise between excessive output voltage ripple and excessive component size and cost. Using this
value of ripple current, the value of inductor, L, is calculated using the following formula:
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