LTM2884IY View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTM2884IY' PDF : 24 Pages View PDF
LTM2884
Applications Information
Hot Plug Protection
The VCC and VBUS 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
greater than 10V that can be hot plugged, add an ad-
ditional 2.2µF tantalum capacitor with greater than 1Ω
of ESR, or a ceramic capacitor with a series 1Ω resistor
to the VCC input to reduce the possibility of exceeding
absolute maximum ratings. Refer to Application Note 88,
“Ceramic Capacitors Can Cause Overvoltage Transients,”
for a detailed discussion of this problem.
PC Board Layout
The high integration of the LTM2884 makes PCB layout
simple. However, to optimize its electrical isolation char-
acteristics, EMI, and thermal performance, some layout
considerations are necessary. The PCB layout in Figure 5
is a recommended configuration for a low EMI USB
application. The following considerations optimize the
performance of the LTM2884:
• Under loaded conditions, VCC and GND current exceed
700mA, VCC2 and GND2 current is up to 500mA. Use
sufficient copper on the PCB to ensure resistive losses
do not cause the supply voltage to drop below the
minimum allowed level. The heavy copper traces will
also help to reduce thermal stress and improve thermal
conductivity.
• Input and output decoupling is not required on peripheral
or hub inputs. Add additional low ESR capacitance to
reduce noise induction on the power supply connec-
tions. Hub/bus splitter outputs require an additional
100µF of low ESR capacitance.
• Do not place copper between the inner columns of
pads on the top or bottom of the PCB. This area must
remain open to withstand the rated isolation voltage
and maintain the creepage distance.
RF, Magnetic Field Immunity
The isolator µModule technology used within the LTM2884
has been independently evaluated, and successfully passed
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,
Electromagnetic Field Immunity
EN 61000-4-8 Power Frequency Magnetic
Field Immunity
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
EN61000-4-8, Level 4 50Hz and 60Hz
EN61000-4-8, Level 5 60Hz
EN61000-4-9, Level 5 Pulse
*Non IEC Method
10V/m
3V/m
1V/m
30A/m
100A/m*
1000A/m
EMI
Radiated emissions have been measured for the LTM2884
using a gigahertz transverse electromagnetic (GTEM) cell
with and without a USB cable attached. The performance
shown in Figure 6 was achieved with the layout structure
in Figure 5. Results are corrected per IEC 61000-4-20.
For more information www.linear.com/LTM2884
2884f
17
Share Link: 
