LTC3554EPD datasheet(25/36 Pages) LINER

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LTC3554

3554f

and DCR losses, and will not give the best efﬁciency. The

choice of which style inductor to use often depends more

on the price versus size, performance and any radiated

EMI requirements than on what the step-down switching

regulators requires to operate.

The inductor value also has an effect on Burst Mode

operation. Lower inductor values will cause Burst Mode

switching frequency to increase.

Input/Output Capacitor Selection

Low ESR (equivalent series resistance) ceramic capacitors

should be used at both step-down switching regulator

outputs as well as at the step-down switching regulator

input supply. Only X5R or X7R ceramic capacitors should

be used because they retain their capacitance over wider

voltage and temperature ranges than other ceramic types.

For good transient response and stability the output capaci-

tor for each step-down switching regulator should retain at

least 4μF of capacitance over operating temperature and

bias voltage. Generally, a good starting point is to use a

10μF output capacitor.

The switching regulator input supply should be bypassed

with a 2.2μF capacitor. Consult with capacitor manufac-

turers for detailed information on their selection and

speciﬁcations of ceramic capacitors. Many manufacturers

now offer very thin (<1mm tall) ceramic capacitors ideal

for use in height-restricted designs. Table 1 shows a list

of several ceramic capacitor manufacturers.

PUSHBUTTON INTERFACE

State Diagram/Operation

Figure 6 shows the LTC3554 pushbutton state diagram.

Figure 6. Pushbutton State Diagram

3554 F06

PUP2

PDN1

PDN2

HRST

POR

PWR_ONx

AND UVLO

PWR_ONx

EXTPWR OR

PB400MS

1SEC

5SEC

1SEC

PON

POFF

PUP1

PWR_ONx

OR UVLO

EXTPWR OR

PB400MS

Upon ﬁrst application of power, VBUS or BAT, an inter-

nal power on reset (POR) signal places the pushbutton

circuitry into the power-down (PDN1) state. One second

after entering the PDN1 state the pushbutton circuitry will

transition into the hard reset (HR) state.

OPERATION

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