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
LM5088
50 PA
C
dither
t
f
SW
x 0.12V
100 x 25 PA
LM5088, LM5088-Q1
SNVS600H –DECEMBER 2008–REVISED MARCH 2013 www.ti.com
The LM5088-1 provides an optional frequency dithering function which is enabled by connecting a capacitor from
the dither pin (DITH) to GND. Connecting the DITH pin directly to GND disables frequency dithering causing the
oscillator to operate at the frequency established by the RT resistor. As shown in Figure 19, the C
dither
capacitor
is used to generate a triangular wave centered at 1.2V. This triangular waveform is used to manipulate the
oscillator circuit such that the oscillator frequency modulates from -5% to +5% of the nominal operating
frequency set by the RT resistor. The C
dither
capacitor value sets the rate of the low frequency modulation i.e., a
lower value C
dither
capacitor will modulate the oscillator frequency from -5% to +5% at a faster rate than a higher
value capacitor. For the dither circuit to work effectively the modulation rate must be much less than the oscillator
frequency (f
SW
), C
dither
should be selected such that;
(6)
whitespace
whitespace
Figure 19. Frequency Dithering Scheme
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