LTC3445 Datasheet, PDF(11/24 Page) Linear Technology – I2C Controllable Buck Regulator with Two LDOs in a 4mm × 4mm QFN

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LTC3445 Datasheet, PDF (11/24 Pages) Linear Technology – I2C Controllable Buck Regulator with Two LDOs in a 4mm × 4mm QFN

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TI I G DIAGRA

SDA

tLOW

tSU(DAT)

SCL

tHD(STA)

START

CONDITION

tHIGH

tHD(DAT)

tSU(STA)

tHD(STA)

REPEATED START

CONDITION

LTC3445

tBUF

tSUSTO

3445 TD

STOP

START

CONDITION CONDITION

I2C Fast Mode Timing Specifications (for Reference)

SYMBOL

fI2C(MAX)

tBUF

tHD(RSTA)

tSU(RSTA)

tSU(STOP)

tHD(DAT)

tSU(DAT)

tLOW

tHIGH

tSP

PARAMETER

Maximum I2C Operating Frequency

Bus Free Time Between Stop and Start Condition

Hold Time After (Repeated) Start Condition

Repeated Start Condition Setup Time

Stop Condition Setup Time

Data Hold Time

Data Setup Time

Clock Low Period

Clock High Period

Pulse Width of Spikes Suppressed by Input Filter

Clock, Data Fall Time (Note 1)

Clock, Data Rise Time (Note 1)

Note 1: CB = Capacitance of one bus line.

MIN TYP MAX

400

1.3

0.6

0.9

100

1.3

0.6

20 + 0.1

300

â¢ CB

20 + 0.1

300

â¢ CB

UNITS

kHz

Âµs

OPERATIO (refer to Figure 1)

BUCK REGULATOR

Main Control Loop

The LTC3445 uses a constant or spread spectrum fre-

quency, current mode step-down architecture (Figure 2).

Both the main (P-channel MOSFET) and synchronous

(N-channel MOSFET) switches are internal. During normal

operation, the internal top power MOSFET is turned on

each cycle when the oscillator sets the RS latch, and

turned off when the current comparator, ICOMP, resets the

RS latch. The peak inductor current at which ICOMP resets

the RS latch is controlled by the output of error amplifier

EA. When the load current increases, it causes a slight

decrease in the feedback voltage, FB, relative to an internal

reference voltage, which in turn, causes the EAâs output

voltage to increase until the average inductor current

matches the new load current. While the top MOSFET is

off, the bottom MOSFET is turned on until either the

inductor current starts to reverse, as indicated by the

current reversal comparator IRCMP, or the beginning of the

next clock cycle.

3445fa

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