LTC3554 Datasheet, PDF (25/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators

LTC3554
OPERATION
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 2 shows a list
of several ceramic capacitor manufacturers.
PUSHBUTTON INTERFACE
State Diagram/Operation
Figure 6 shows the LTC3554 pushbutton state diagram.
PUP2
HR
EXTPWR OR
PB400MS
EXTPWR OR
PB400MS
5SEC
PUP1
PWR_ONx 1SEC
5SEC
POFF
1SEC
PWR_ONx
AND UVLO
PON
HRST
PWR_ONx
OR UVLO
PDN2
HRST
HRST
PDN1
POR
3554 F06
Figure 6. Pushbutton State Diagram
Upon first application of power, V_BUS 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.
3554p
25