LTM2886 datasheet(24/38 Pages) AD

24 / 38 page

LTM2886

Rev C

For more information www.analog.com/LTM2886

APPLICATIONS INFORMATION

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 lowpass filter (R = 500Ω,

C = 100pF) can be used to increase 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 printed circuit board or route with ground between.

If these signals are wired off board, twist SCL2 with VCC2

and/or GND2 and SDA2 with GND2 and/or VCC2, 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.

Low Noise Applications

For precision analog applications the V+ and V– power

rails may be filtered to improve the noise performance.

Figure 14 shows the recommended component values to

reduce noise at high frequencies. The selected inductor

should be chosen such that the parasitic capacitance is

low enough to keep the self resonant frequency greater

than 10MHz. The plots of Figures 15 and 16 show the high

frequency noise improvement for the V+ rail, the improve-

ment on the V– rail will be nearly equivalent.

Some applications may require the noise performance be

improved in the 100Hz to 10kHz region. An additional LC

filter stage may be added between the LTM2886 and the

high frequency filter to lower the noise corner frequency.

Using an inductance of 330µH and capacitance of 680µF

reduces the noise corner to approximately 340Hz. The

RMSnoiseatabandwidthof340Hzisapproximately22µV.

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

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

Figure 14. Filtered Voltage Rails for Low Noise Applications

CBUS (pF)

100

2886 F12

1000

VL = 3V

VL = 3.3V

VL = 3.6V

VL = 4.5V TO 5.5V

CBUS (pF)

100

2886 F13

1000

VL = 3V

VL = 3.3V

VL = 3.6V

VL = 4.5V TO 5.5V

CS2

LTM2886-5S

VCC

GND

SDI

SDI2

SDOE

SCK

DO2

SCK2

V–

AVCC2

V+

VCC2

SDO

SDO2

DO1

GND2

22µH

FILTERED V+

FILTERED V–

2886 F15

10µF

22µH

LTM2886 Datasheet(PDF) 24 Page - Analog Devices

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