LTC4100EGPBF LINER [Linear Technology], LTC4100EGPBF Datasheet - Page 26

• Manufacturer Part Number: LTC4100EGPBF
• Description: Smart Battery Charger Controller
• Manufacturer: LINER [Linear Technology]

LTC4100
APPLICATIONS INFORMATION
Protecting SMBus Inputs
The SMBus inputs, SCL and SDA, are exposed to uncon-
trolled transient signals whenever a battery is connected
to the system. If the battery contains a static charge, the
SMBus inputs are subjected to transients which can cause
damage after repeated exposure. Also, if the battery’s posi-
tive terminal makes contact to the connector before the
negative terminal, the SMBus inputs can be forced below
ground with the full battery potential, causing a potential
for latch-up in any of the devices connected to the SMBus
inputs. Therefore it is good design practice to protect the
SMBus inputs as shown in Figure 10.
SafetySignal (Thermistor) Value
The SafetySignal (typical application on back page), is a
multifunction signal the communicates three pieces of
information in order of importance:
1) Presence of the Smart Battery
2) The maximum time duration of the wake-up charge
3) An optional and redundant temperature measurement
The value of the resistance to ground communicates all
this information. The resistance ranges and what it does
is covered by the SBS Smart Battery Charger standard in
Section 6. Basically if you have a battery chemistry, such
as Li-ion, that cannot safely withstand an infi nite dura-
tion wake-up charge, the SafetySignal resistance value
needs to be less than 425Ω. The popular value to use is
a fi xed 300Ω resistor. Otherwise the resistance value is
10k which is normally expected to be done using a 10k
NTC resistor.
26
allowed.
system.
V
IN
Figure 10. Recommended SMBus Transient Protection
Figure 12. Kelvin Sensing of Charging Current
C2
Figure 11. High Speed Switching Path
CONNECTOR
TO BATTERY
CIRCULATING
FREQUENCY
DIRECTION OF CHARGING CURRENT
SWITCH NODE
PATH
HIGH
VIAS TO CSP AND BAT
R
SENSE
V
DD
L1
D1
TO SYSTEM
4100 F12
4100 F10
C4
BAT
4100 F11
4100fb
V
BAT