Datasheet

DITHER
+
-
Q
Q
R
S
+
-
Oscillator
T
osc
+
't
T
osc
T
osc
-
't
1.26V
C
dither
+5V
25 PA
1.14V
1.26V
1.20V
1.14V
LM25088
50 PA
LM25088
LM25088-Q1
www.ti.com SNVS609H –DECEMBER 2008–REVISED MARCH 2013
Figure 19. Frequency Dithering Scheme
Figure 20. Conducted Emissions Measured at the Input of a LM25088 Based Buck Converter
Figure 20 shows the conducted emissions on the LM25088 evaluation board input power line. It can be seen
from the above picture that, the peak emissions with non-dithering operation are centered narrowly at the
operating frequency of the converter. With dithering operation, the conducted emissions are spread around the
operating frequency and the maximum amplitude is reduced by approximately 10dB. (Figure 20 was captured
using a Chroma DC power supply model number 62006P and an Agilent network analyzer model number
4395A).
Cycle-by-Cycle Current Limit
The LM25088 contains a current limit feature that protects the circuit from extended over current conditions. The
emulated current signal is directly proportional to the buck switch current and is applied to the current limit
comparator. If the emulated current exceeds 1.2V, the PWM cycle is terminated. The peak inductor current
required to trigger the current limit comparator is given by:
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