Datasheet

LTC4160/LTC4160-1
22
41601fa
APPLICATIONS INFORMATION
There are MLCCs available with several types of dielectrics
each having considerably different characteristics. For
example, X7R MLCCs have the best voltage and tempera-
ture stability. X5R MLCCs have apparently higher packing
density but poorer performance over their rated voltage
and temperature ranges. Y5V MLCCs have the highest
packing density, but must be used with caution, because
of their extreme nonlinear characteristic of capacitance
versus voltage. The actual in-circuit capacitance of a
ceramic capacitor should be measured with a small AC
signal and DC bias as is expected in-circuit. Many vendors
specify the capacitance versus voltage with a 1V
RMS
AC
test signal and, as a result, over state the capacitance that
the capacitor will present in the application. Using similar
operating conditions as the application, the user must
measure or request from the vendor the actual capacitance
to determine if the selected capacitor meets the minimum
capacitance that the application requires.
Overvoltage Protection
V
BUS
can be protected from overvoltage damage with two
additional components, a resistor R1 and an N-channel
MOSFET MN1, as shown in Figure 5. Suitable choices for
MN1 are listed in Table 4.
Table 4. Recommended N-Channel MOSFETs for the Overvoltage
Protection Circuit
PART # BVDSS R
ON
PACKAGE
Si1472DH 30V 57mΩ SC70-6
Si2302ADS 20V 60mΩ SOT-23
Si2306BDS 30V 47mΩ SOT-23
Si2316DS 30V 50mΩ SOT-23
IRLML2502 20V 50mΩ SOT-23
FDN372S 30V 50mΩ SOT-23
NTLJS4114N 30V 35mΩ WDFN6
R1 is a 6.2k resistor and must be rated for the power dis-
sipated during maximum overvoltage. In an overvoltage
condition the OVSENS pin will be clamped at 6V. R1 must
be sized appropriately to dissipate the resultant power.
For example, a 1/10W 6.2k resistor can have at most
√(PMAX • 6.2kΩ) = 25V applied across its terminals. With
the 6V at OVSENS, the maximum overvoltage magnitude
that this resistor can withstand is 31V. A 1/4W 6.2k resis-
tor raises this value to 45V. OVSENS’s absolute maximum
current rating of 10mA imposes an upper limit of 68V
protection.
Reverse Voltage Protection
The LTC4160/LTC4160-1 can also be easily protected
against the application of reverse voltages, as shown in
Figure 6. D1 and R1 are necessary to limit the maximum
V
GS
seen by MP1 during positive overvoltage events. D1’s
breakdown voltage must be safely below MP1’s BVGS. The
circuit shown in Figure 6 offers forward voltage protection
up to MN1’s BVDSS and reverse voltage protection up to
MP1’s BVDSS.
Figure 5. Overvoltage Protection
Figure 6. Dual Polarity Voltage Protection
R1
USB/WALL
ADAPTER
41601 F05
C1
MN1
V
BUS
OVSENS
OVGATE
LTC4160/
LTC4160-1
Battery Charger Over Programming
The USB high power specification allows for up to 2.5W
to be drawn from the USB port. The LTC4160/LTC4160-1’s
bidirectional switching regulator in step-down mode con-
verts the voltage at V
BUS
to a voltage just above BAT on
V
OUT
, while limiting power to less than the amount pro-
grammed at CLPROG. The charger should be programmed
(with the PROG pin) to deliver the maximum safe charging
current without regard to the USB specifications. If there
is insufficient current available to charge the battery at the
programmed rate, the charge current will be reduced until
the system load on V
OUT
is satisfied and the V
BUS
cur-
rent limit is satisfied. Programming the charger for more
R2R1
USB/WALL
ADAPTER
41601 F06
C1D1
MN1MP1
V
BUS
POSITIVE PROTECTION UP TO BVDSS OF MN1
V
BUS
NEGATIVE PROTECTION UP TO BVDSS OF MP1
V
BUS
OVSENS
OVGATE
LTC4160/
LTC4160-1