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Data Sheet

ADL8154

RECOMMENDED POWER MANAGEMENT CIRCUIT

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Rev. 0 | 22 of 23

Figure 84 shows a recommended power management circuit for the

ADL8154. The LT8607 step-down regulator is used to step down a

12 V rail to 6.5 V, which is then applied to the LT3045 low dropout

(LDO) linear regulator to generate a low noise 5 V output. The 5.5

V regulator output (VREG) of the LT8607 is set by the R4A and R5A

resistors, according to the following equation:

R5A= R4AVREG0.778−1

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

resistor (R2A) on the RT pin of the LT8607. The LT8607 data sheet

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

switching frequencies ranging from 0.2 MHz to 2.2 MHz.

The output voltage (VOUT) of the LT3045 is set by the R3B resistor

connected to the SET pin, according to the following equation:

R3B= VOUT100 μA

The resistors on the PGFB pins of LT3045 are chosen to trigger the

power-good (PG) signal when the output reaches 90% of its target

voltage of 5 V. The PG open-collector output is pulled up to the 5 V

output to give a convenient 0 V or 5 V output voltage.

Table 11 provides the recommended resistor values to set the

VOUT of the LT3045 and the PG threshold at 90% for various

VOUT values. Table 11 also provides the required resistor values to

set the VOUT of the LT8607 to 500 mV greater than the VOUT of

the LT3045. Note that the dropout voltage of the LT3045 can be

reduced to a minimum of 350 mA for output currents up to 200 mA.

The LT8607 can source a maximum current of 750 mA, and the

LT3045 can source a maximum current of 500 mA. If the 5 V power

supply voltage is being developed as a bus supply to serve another

component, higher current devices can be used. The LT8608 and

LT8609 step-down regulators can source a maximum current to 1.5

A and 3 A, respectively, and these devices are pin compatible with

the LT8607.

Table 11. Recommended Resistor Values for Operating at 4 V to 5.5 V

LT3045 LDO VOUT and PG Threshold

LT8607 Regulator VOUT

VOUT (V)

R3B (kΩ)

R5B (kΩ)

R6B (kΩ)

Recommended VREG (V)

R4A (MΩ)

R5A (kΩ)

40.2

453

41.2

4.5

210

4.5

453

33.6

5.0

184

49.9

453

32.4

5.5

165

5.5

453

29.2

6.0

149

Figure 84. Recommended Power Management Circuit

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