LTM2886 datasheet(12/18 Pages) AD

12 / 18 page

LTM2894

Rev A

For more information www.analog.com

APPLICATIONS INFORMATION

Supply Current Equations (Typical)

Operating:

IBUS = 6mA +IVLO

IBUS2 = 6mA +IVLO2

Suspend:

IBUSSPND = 1.5mA +IVLO

IBUS2SPND = 6mA +IVLO2

Off :

IBUSPOFF = 10µA

IBUS2POFF = 10µA

USB 2.0 Compatibility

The LTM2894 µModule transceiver is compatible with the

USB2.0specificationoffullandlowspeedoperation.Some

characteristics of the LTM2894 µModule transceiver may

notsupportfullcompliancewiththeUSB2.0specification.

The propagation delay for full speed data of 80ns exceeds

the specification for a single hub of 44ns plus the at-

tached cable delay of 26ns. This results from driving the

data signal to the 3.3V rail prior to a K-state transition to

maintain balanced crossover voltages equivalent to the

cross over voltages of the successive data transitions.

USB ports commonly drive the idle state bus to the 3.3V

rail prior to the K-state start of packet transition. Further,

the LTM2894 does not re-time the data transitions, and

will propagate the edges as received, with the potential to

add additional jitter or pulse width distortion.

Hot Plug Protection

The VBUS and VBUS2 inputs are bypassed with low ESR

ceramic capacitors. During a hot-plug event, the supply

inputs can overshoot the supplied voltage due to cable

inductance. When using external power supply sources

greaterthan24Vthatcanbehot-plugged,addanadditional

2.2µF tantalum capacitor with greater than 1Ω of ESR, or

a ceramic capacitor with a series 1Ω resistor to the VBUS

or VBUS2 input to reduce the possibility of exceeding ab-

solute maximum ratings. Refer to Application Note AN88,

Ceramic Capacitors Can Cause Overvoltage Transients, for

a detailed discussion of this problem.

PC Board Layout

The high integration of the LTM2894 makes PCB lay-

out simple. However, to optimize its electrical isolation

characteristics, and EMI, some layout considerations are

necessary. The PCB layout in Figure 5 is a recommended

configuration for a low EMI USB application. The following

considerationsoptimizetheperformanceoftheLTM2894.

• Do not place copper between the inner columns of

pads on the top or bottom on the PCB. This area must

remain open to withstand the rated isolation voltage

and maintain the creepage distance.

• Route D1– and D1+ and D2– and D2+ as differential

pairs with 90Ω impedance, matching the USB cable

impedance.

RF, Magnetic Field Immunity

TheisolatorµModuletechnologyusedwithintheLTM2894

hasbeenindependentlyevaluated,andsuccessfullypassed

the RF and magnetic field immunity testing requirements

per European Standard EN 55024, in accordance with the

following test standards:

EN 61000-4-3 Radiated, Radio-Frequency, Electromag-

netic Field Immunity

EN 61000-4-8 PowerFrequencyMagneticFieldImmunity

EN 61000-4-9 Pulsed Magnetic Field Immunity

Tests were performed using an unshielded test card de-

signed per the data sheet PCB layout recommendations.

Specific limits per test are detailed in Table 2.

Table 2. Test Frequency Field Strength

EN 61000-4-3, Annex D, 80MHz to 1GHz

1.4MHz to 2GHz

2GHz to 2.7GHz

10V/m

3V/m

1V/m

EN 61000-4-8, Level 4 50Hz and 60Hz

30A/m

EN 61000-4-8, Level 5 60Hz

100A/m*

EN 61000-4-9, Level 5 Pulse

1000A/m

*Non-IEC Method

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