LLTC4100EG View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LLTC4100EG' PDF : 30 Pages View PDF
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
allowed.
3) An optional and redundant temperature measurement
system.
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 infinite duration
wake-up charge, the SafetySignal resistance value needs
to be less than 425Ω. The popular value to use is a fixed
300Ω resistor. Otherwise the resistance value is 10k which
is normally expected to be done using a 10k NTC resistor.
VDD
CONNECTOR
TO BATTERY
TO SYSTEM
4100 F10
Figure 10. Recommended SMBus Transient Protection
SWITCH NODE
HIGH
VIN
C2
FREQUENCY
CIRCULATING
PATH
L1
VBAT
D1
C4
BAT
4100 F11
Figure 11. High Speed Switching Path
DIRECTION OF CHARGING CURRENT
RSENSE
VIAS TO CSP AND BAT
4100 F12
Figure 12. Kelvin Sensing of Charging Current
4100fc
26
For more information www.linear.com/LTC4100
Share Link: 
