Datasheet

LM22680-ADJ
+
GND
+
VIN
EN
SW
BOOT
FB
GND
RT/SYNC
VIN 4.5V to 42V
C2
22 PF
C1
6.8 PF
EN
SYNC
R3
C3
10 nF
L1
12 PH
C4
120 PF
GND
R
FBT
1.54 k:
R
FBB
976:
D1
60V, 5A
VOUT 3.3V
SS
C6
100 1k 10k 100k 1M 10M
10
15
20
25
30
35
40
COMPENSATOR GAIN (dB)
FREQUENCY (Hz)
LM22680
SNVS595K –SEPTEMBER 2008–REVISED APRIL 2013 www.ti.com
(9)
Alternatively, this pole should be placed between 1.5kHz and 15kHz and is given by the equation shown below:
(10)
The Q factor depends on the parasitic resistance of the power stage components and is not typically in the
control of the designer. Of course, loop compensation is only one consideration when selecting power stage
components; see the Application Information section for more details.
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 2A. See
AN-1911 (SNVA378) 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 LM22680.
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