LM3488

LM3488-Q1

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SNVS089M – JULY 2000 – REVISED MARCH 2013

The LM3488 can be synchronized to an external clock. The external clock must be connected to the

Table 1.

1

5 to 13

2

20 to 40

3

40 to 65

4

55 to 90

5

70 to 110

6

85 to 140

7

100 to 160

8

120 to 190

9

135 to 215

10

150 to 240

It is also necessary to have the width of the synchronization pulse wider than the duty cycle of the converter

(when DR pin is high and the switching point is low). It is also necessary to have the synchronization pulse width

≥ 300nsecs.

The FA/SYNC/SD pin also functions as a shutdown pin. If a high signal (see Electrical Characteristics for

definition of high signal) appears on the FA/SYNC/SD pin, the LM3488 stops switching and goes into a low

current mode. The total supply current of the IC reduces to less than 10µA under these conditions.

Figure 29 and Figure 30 show implementation of shutdown function when operating in Frequency adjust mode

and synchronization mode respectively. In frequency adjust mode, connecting the FA/SYNC/SD pin to ground

forces the clock to run at a certain frequency. Pulling this pin high shuts down the IC. In frequency adjust or

synchronization mode, a high signal for more than 30µs shuts down the IC.

Figure 27. Frequency Adjust

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