Datasheet

UCD3138
www.ti.com SLUSAP2F –MARCH 2012–REVISED NOVEMBER 2013
3.5 PMBus/SMBus/I
2
C Timing
The timing characteristics and timing diagram for the communications interface that supports I
2
C, 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. I
2
C/SMBus/PMBus Timing Characteristics
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Typical values at T
A
= 25°C and VCC = 3.3 V (unless otherwise noted)
f
SMB
SMBus/PMBus operating frequency Slave mode, SMBC 50% duty cycle 100 1000 kHz
f
I2C
I
2
C 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 0 ns
t
(SU:DAT)
Data setup time 100 ns
t
(TIMEOUT)
Error signal/detect
(2)
35 ms
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)
25 ms
time
(4)
20 + 0.1
t
f
Clock/data fall time Rise time t
r
= (V
ILmax
– 0.15) to (V
IHmin
+ 0.15) 300 ns
Cb
(5)
20 + 0.1
t
r
Clock/data rise time Fall time t
f
= 0.9 VDD to (V
ILmax
– 0.15) 300 ns
Cb
(5)
C
b
Total capacitance of one bus line 400 pF
(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) C
b
(pF)
Figure 3-1. I
2
C/SMBus/PMBus Timing Diagram
Copyright © 2012–2013, Texas Instruments Incorporated Electrical Specifications 19
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