LTC4075EDD#PBF Linear Technology, LTC4075EDD#PBF Datasheet - Page 14

• Manufacturer Part Number: LTC4075EDD#PBF
• Description: IC CHARG BATT LI-ON USB 10DFN
• Manufacturer: Linear Technology

Specifications of LTC4075EDD#PBF

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 4.3 V ~ 8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-WFDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
makes them especially susceptible to this problem. To
bypass the USB pin and the wall adapter input, add a 1Ω
resistor in series with a ceramic capacitor to lower the
effective Q of the network and greatly reduce the ringing.
A tantalum, OS-CON, or electrolytic capacitor can be used
in place of the ceramic and resistor, as their higher ESR
reduces the Q, thus reducing the voltage ringing.
The oscilloscope photograph in Figure 4 shows how
serious the overvoltage transient can be for the USB
and wall adapter inputs. For both traces, a 5V supply is
hot-plugged using a three foot long cable. For the top
trace, only a 4.7µF capacitor (without the recommended
1Ω series resistor) is used to locally bypass the input.
This trace shows excessive ringing when the 5V cable
is inserted, with the overvoltage spike reaching 10V. For
the bottom trace, a 1Ω resistor is added in series with the
4.7µF capacitor to locally bypass the 5V input. This trace
shows the clean response resulting from the addition of
the 1Ω resistor.
Even with the additional 1Ω resistor, bad design techniques
and poor board layout can often make the overvoltage
LTC4075/LTC4075X
14
4.7µF ONLY
4.7µF + 1Ω
Figure 4. Waveforms Resulting from Hot-Plugging a
5V Input Supply
2V/DIV
2V/DIV
U
U
20µs/DIV
W
3455 F04
U
problem even worse. System designers often add extra
inductance in series with input lines in an attempt to mini-
mize the noise fed back to those inputs by the application.
In reality, adding these extra inductances only makes the
overvoltage transients worse. Since cable inductance is
one of the fundamental causes of the excessive ringing,
adding a series ferrite bead or inductor increases the ef-
fective cable inductance, making the problem even worse.
For this reason, do not add additional inductance (ferrite
beads or inductors) in series with the USB or wall adapter
inputs. For the most robust solution, 6V transorbs or zener
diodes may also be added to further protect the USB and
wall adapter inputs. Two possible protection devices are
the SM2T from STMicroelectronics and the EDZ series
devices from ROHM.
Always use an oscilloscope to check the voltage wave-
forms at the USBIN and DCIN pins during USB and wall
adapter hot-plug events to ensure that overvoltage
transients have been adequately removed.
Reverse Polarity Input Voltage Protection
In some applications, protection from reverse polarity
voltage on the input supply pins is desired. If the sup-
ply voltage is high enough, a series blocking diode can
be used. In other cases where the voltage drop must be
kept low, a P-channel MOSFET can be used (as shown in
Figure 5).
Figure 5. Low Loss Input Reverse Polarity Protection
ADAPTER
WALL
DIODE OF FET
DRAIN-BULK
DCIN
LTC4075
4075 F05
4075Xfa