LT3045 datasheet(24/45 Pages) AD

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Data Sheet

LT83201

analog.com

Rev. A 24 of 45

Synchronization

To synchronize the LT83201 oscillator to an external frequency, connect a square wave to the SYNC/MODE pin. The

square wave amplitude should have valleys below 0.7V and peaks above 1.5V (up to 6V), with a minimum on-time

and off-time of 50ns.

While synchronized to an external clock, the part runs in FCM to maintain regulation. The LT83201 may be

synchronized over a 300kHz to 6MHz range. The RT resistor should be chosen to set the LT83201 switching frequency

to be equal to the synchronization input. The slope compensation is set by the RT value, while the minimum slope

compensation required to avoid subharmonic oscillations is established by the inductor size, input voltage, and

output voltage.

Setting the Switching Frequency

The LT83201 uses constant-frequency PWM architecture that is programmed to switch from 300kHz to 6MHz by using

a resistor connected from the RT pin to GND.

The RT resistor required for the desired switching frequency is calculated by Equation 1.

RT =

115.8

fSW

− 10.4

(1)

where RT is in kΩ and fSW is the desired switching frequency in MHz. Table 4 shows the necessary RT value for the

desired switching frequency.

Table 4. SW Frequency vs. RT Value

fSW (MHz)

RT (kΩ)

0.3

392

0.4

287

0.5

226

0.6

187

0.7

154

0.8

137

0.9

118

1.0

105

1.2

86.6

1.4

71.5

1.6

61.9

1.8

53.6

47.5

2.5

35.7

28.7

3.5

23.2

18.0

9.76

Operating Frequency Selection and Trade-Offs

Selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. The

advantage of high-frequency operation is that smaller inductor and capacitor values may be used. The

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