ltc4097 Linear Technology Corporation, ltc4097 Datasheet - Page 18

• Manufacturer Part Number: ltc4097
• Description: Usb/wall Adapter Standalone Li-ion/polymer Battery Charger
• Manufacturer: Linear Technology Corporation

LTC4097
APPLICATIONS INFORMATION
the nearest 1% value is 105k.
the nearest 1% value is 12.7k. The fi nal solution is shown
in Figure 5 and results in an upper trip point of 45°C and
a lower trip point of 0°C.
Protecting the USB Pin and Wall Adapter Input from
Overvoltage Transients
Caution must be exercised when using ceramic capaci-
tors to bypass the USBIN or the wall adapter inputs. High
voltage transients can be generated when the USB or wall
adapter is hot plugged. When power is supplied via the
USB bus or wall adapter, the cable inductance along with
the self resonant and high Q characteristics of ceramic
capacitors can cause substantial ringing which could
exceed the maximum voltage ratings and damage the
LTC4097. Refer to Linear Technology Application Note 88,
entitled “Ceramic Input Capacitors Can Cause Overvoltage
Transients” for a detailed discussion of this problem.
18
R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k
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 6).
Figure 6. Low Loss Input Reverse Polarity Protection
ADAPTER
WALL
DIODE OF FET
DRAIN-BULK
DCIN
LTC4097
4097 F06
4097f