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LTC4313-1/LTC4313-2/

LTC4313-3

4313123f

The LTC4313 provides capacitance buffering, data and

clock Hot Swap capability and level translation. The high

noise margin of the LTC4313 permits interoperability with

I2C devices that drive a high VOL permits series connec-

tion of multiple LTC4313s and improves I2C communica-

tion reliability. The LTC4313 isolates backplane and card

capacitances and provides slew control of falling edges

while level translating 3.3V and 5V busses. The LTC4313-1

and LTC4313-2 also provide pull-up currents to accelerate

rising edges. These features are illustrated in the following

subsections.

Rise Time Accelerator (RTA) Pull-Up Current Strength

(LTC4313-1 and LTC4313-2)

Afteraninputandoutputconnectionhasbeenestablished,

the RTAs on both the input and output sides of the SDA

and SCL busses are activated. During positive bus transi-

tions of at least 0.4V/µs, the RTAs provide pull-up cur-

rents to reduce rise time. The RTAs allow users to choose

larger bus pull-up resistors to reduce power consumption

and improve logic low noise margins, design with bus

capacitances outside of the I2C specification or to oper-

ate at a higher clock frequency. The LTC4313-1 regulates

its RTA current to limit the bus rise rate to a maximum

applicaTions inForMaTion

Figure 1. Bus Rising Edge for the LTC4313-1. VCC = VDD,BUS = 5V

Figure 2. Bus Rising Edge for the LTC4313-2. VCC = VDD,BUS = 5V

of 75V/µs. The current is therefore directly proportional

to the bus capacitance. The LTC4313-1 RTA is capable of

sourcing up to 40mA of current. Rise time acceleration

for the LTC4313-2 is provided by a 2.5mA current source.

Figures 1 and 2 show the rising waveforms of heavily

loaded SDAIN and SDAOUT busses for the LTC4313-1 and

LTC4313-2 respectively. In both figures, during a rising

edge, the buffers are active and the input and output sides

are connected, until the bus voltages on both the input

and output sides are greater than 0.3 • VCC. When each

individual bus voltage rises above 0.41 • VCC, the RTA on

that bus turns on. The effect of the acceleration strength

is shown in the waveforms in Figures 1 and 2 for identi-

cal bus loads. The RTAs of the LTC4313-1 and LTC4313-2

supply10mAand2.5mAofpull-upcurrentrespectivelyfor

the bus conditions shown in Figures 1 and 2. For identical

bus loads, the bus rises faster in Figure 1 compared to

Figure 2 because of the higher IRTA.

The RTAs are internally disabled during power-up and dur-

ing a bus stuck low event. The RTAs when activated pull

the bus up to 0.9•VCC on the input and output sides of the

SDA and SCL pins. In order to prevent bus overdrive by

the RTA, the bus supplies on the input and output sides

2V/DIV

1µs/DIV

4313123 F01

VCC = VDD,BUS = 5V

RBUS = 20k

CIN = COUT = 200pF

SDAIN

SDAOUT

2V/DIV

1µs/DIV

4313123 F02

VCC = VDD,BUS = 5V

RBUS = 20k

CIN = COUT = 200pF

SDAIN

SDAOUT

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