LTC7151S datasheet(24/44 Pages) AD

24 / 44 page

Data Sheet

LT83203/LT83205

analog.com

Rev. B

24 of 44

Synchronization

To synchronize the LT83203/LT83205 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 LT83203/LT83205 may be

synchronized over a 300kHz to 6MHz range. The RT resistor should be chosen to set the LT83203/LT83205 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 LT83203/LT83205 uses a 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

LTC7151S Datasheet(PDF) 24 Page - Analog Devices

LTC7151S Datasheet(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datasheet Download

Link URL