LM46000 Datasheet, PDF (19/56 Pages) Texas Instruments – LM46000 SIMPLE SWITCHER® 3.5 V to 60 V 0.5 A Synchronous Step-Down Voltage Converter

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Feature Description (continued)
LM46000
SNVSA45A – JUNE 2014 – REVISED JULY 2014
Enable
Internal SS Ramp
Ext Tracking Signal to SS pin
VOUT
Figure 38. Tracking with Longer Start-up Time Than The Internal Ramp
Enable
Internal SS Ramp
Ext Tracking Signal to SS pin
VOUT
Figure 39. Tracking with Shorter Start-up Time Than The Internal Ramp
7.3.7 Switching Frequency (RT) and Synchronization (SYNC)
The switching frequency of the LM46000 can be programmed by the impedance R_T from the RT pin to ground.
The frequency is inversely proportional to the R_T resistance. The RT pin can be left floating and the LM46000 will
operate at 500 kHz default switching frequency. The RT pin is not designed to be shorted to ground.
For a desired frequency, typical R_T resistance can be found by Equation 3.
R_T(kΩ) = 40200 / Freq (kHz) - 0.6
(3)
Figure 40 shows R_T resistance vs switching frequency F_S curve.
250
200
150
100
50
0
0
500
1000
1500
2000
2500
Switching Frequency (kHz)
C008
Figure 40. R_T Resistance vs Switching Frequency
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