Data Sheet

ADL7078

RECOMMENDED POWER MANAGEMENT CIRCUIT

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Rev. 0 | 17 of 19

Figure 53 shows the recommended power management circuit for

the ADL7078. The LT8607 step-down regulator is used to step

down a 12 V rail to 6.62 V, which is then applied to the LT3042 low

dropout (LDO) linear regulator to generate a low noise 5 V output.

While the circuit shown in Figure 53 has an input voltage (VIN) of 12

V, the input range to the LT8607 can be as high as 42 V.

The 6.62 V regulator output of the LT8607 is set by the R2 and R3

resistors according to the following equation:

R2 = R3((VOUT/0.778 V) − 1), where VOUT is the output voltage.

The switching frequency (fSW) is set to 2 MHz by the 18.2 kΩ

resistor on the RT pin of the LT8697. The LT8607 data sheet

provides a table of resistor values that can be used to select other

fSW values ranging from 0.2 MHz to 2.200 MHz.

VOUT = 100 μA × R4

The PGFB resistors of the LT3042 are chosen to trigger the power-

good (PG) signal when the output is just under 95% of the target

voltage of 5 V. The output of the LT3042 has 1% initial tolerance

and another 1% variation over temperature. The PGFB tolerance is

roughly 3% over temperature and adding resistors results in a bit

more (5%), therefore, putting 5% between the output and the PGFB

resistors works well. In addition, the PG open collector is pulled up

to the 5 V output to give a convenient 0 V to 5 V voltage range.

Figure 53. Recommended Power Management Circuit