LTM2887 datasheet(23/30 Pages) AD

23 / 30 page

LTM2810

Rev. A

For more information www.analog.com

APPLICATIONS INFORMATION

The logic side bidirectional serial data pin, SDA, requires a

pull-up resistor or current source connected to VL. Follow

the requirements in Figure 12 and Figure 13 for the ap-

propriate pull-up resistor on SDA that satisfies the desired

rise time specifications and VOL maximum limits for fast

and standard modes. The resistance curves represent the

maximum resistance boundary; any value may be used to

the left of the appropriate curve.

The isolated side clock pin, SCL2, has a weak push-pull

output driver; do not connect an external pull-up device.

SCL2 is compatible with I2C devices without clock stretch-

ing. On lightly loaded connections, a 100pF capacitor

from SCL2 to GND2 or RC low pass filter (R = 500Ω,

C = 100pF) can be used to decrease the rise and fall times

and minimize noise.

Some consideration must be given to signal coupling

between SCL2 and SDA2. Separate these signals on a

printedcircuitboardorroutewithgroundbetween.Ifthese

signals are wired off board, twist SCL2 with VL2 and/or

GND2 and SDA2 with GND2 and/or VL2; do not twist SCL2

and SDA2 together. If coupling between SCL2 and SDA2

is unavoidable, place the aforementioned RC filter at the

SCL2 pin to reduce noise injection onto SDA2.

CBUS (pF)

100

2810 F12

1000

VL = 3V

VL = 3.3V

VL = 3.6V

VL = 4.5V TO 5.5V

CBUS (pF)

100

2810 F13

1000

VL = 3V

VL = 3.3V

VL = 3.6V

VL = 4.5V TO 5.5V

Figure 12. Maximum Standard Speed Pull-Up Resistance on SDA

Figure 13. Maximum Fast Speed Pull-Up Resistance on SDA

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