UCD3138RMHT datasheet(19/78 Pages) TI1

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UCD3138

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SLUSAP2F – MARCH 2012 – REVISED NOVEMBER 2013

3.5

PMBus/SMBus/I

2C Timing

The timing characteristics and timing diagram for the communications interface that supports I2C, SMBus,

and PMBus in Slave or Master mode are shown in Table 3-1, Figure 3-1, and Figure 3-2. The numbers in

Table 3-1 arµe for 400 kHz operating frequency. However, the device supports all three speeds, standard

(100 kHz), fast (400 kHz), and fast mode plus (1 MHz).

Table 3-1. I2C/SMBus/PMBus Timing Characteristics

PARAMETER

TEST CONDITIONS

MIN

TYP MAX

UNIT

Typical values at TA = 25°C and VCC = 3.3 V (unless otherwise noted)

fSMB

SMBus/PMBus operating frequency

Slave mode, SMBC 50% duty cycle

100 1000

kHz

fI2C

I2C operating frequency

Slave mode, SCL 50% duty cycle

100 1000

kHz

Bus free time between start and

t(BUF)

1.3

µs

stop(1)

t(HD:STA)

Hold time after (repeated) start(1)

0.6

µs

t(SU:STA)

Repeated start setup time(1)

0.6

µs

t(SU:STO)

Stop setup time(1)

0.6

µs

t(HD:DAT)

Data hold time

Receive mode

t(SU:DAT)

Data setup time

100

t(TIMEOUT)

Error signal/detect(2)

t(LOW)

Clock low period

1.3

µs

t(HIGH)

Clock high period(3)

0.6

µs

Cumulative clock low slave extend

t(LOW:SEXT)

time(4)

20 + 0.1

Clock/data fall time

Rise time tr = (VILmax – 0.15) to (VIHmin + 0.15)

300

Cb(5)

20 + 0.1

Clock/data rise time

Fall time tf = 0.9 VDD to (VILmax – 0.15)

300

Cb(5)

Total capacitance of one bus line

400

(1)

Fast Mode, 400 kHz

(2)

The device times out when any clock low exceeds t(TIMEOUT).

(3)

t(HIGH), Max, is the minimum bus idle time. SMBC = SMBD = 1 for t > 50 ms causes reset of any transaction that is in progress. This

specification is valid when the NC_SMB control bit remains in the default cleared state (CLK[0] = 0).

(4)

t(LOW:SEXT) is the cumulative time a slave device is allowed to extend the clock cycles in one message from initial start to the stop.

(5)

Cb (pF)

Figure 3-1. I2C/SMBus/PMBus Timing Diagram

Electrical Specifications

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