LLTC4100EG View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LLTC4100EG' PDF : 30 Pages View PDF
LTC4100
Operation
SafetySignal sensing is accomplished by a state machine
that reconfigures the switches of Figure 4 using THA_SELB
and THB_SELB, a selectable reference generator, and two
comparators. This circuit has two modes of operation
based upon whether AC is present.
When AC is present, the LTC4100 samples the value of
the SafetySignal and updates the ChargerStatus register
approximately every 32ms. The state machine successively
samples the SafetySignal value starting with the RES_OR
≥ RES_COLD threshold, then RES_C0LD ≥ RES_IDEAL
threshold, RES_IDEAL ≥ RES_HOT threshold, and finally
the RES_HOT ≥ RES_UR threshold. Once the SafetySignal
range is determined, the lower value thresholds are
not sampled. The SafetySignal decoder block uses the
previously determined SafetySignal value to provide the
appropriate adjustment in threshold to add hysteresis.
The RTHB resistor value is used to measure the RES_OR
≥ RES_COLD and RES_COLD ≥ RES_IDEAL thresholds by
connecting the THB pin to VDD and measuring the voltage
resultant on the THA pin. The RTHA resistor value is used
to measure the RES_IDEAL ≥ RES_HOT and RES_HOT ≥
RES_UR thresholds by connecting the THA pin to VDD and
measuring the voltage resultant on the THB pin.
The SafetySignal decoder block uses a voltage divider
network between VDD and GND to determine SafetySig-
nal range thresholds. Since the THA and THB inputs are
sequentially connected to VDD, this provides VDD noise
immunity during SafetySignal measurement.
When AC power is not available the SafetySignal block
supports the following low power operating features:
1. The SafetySignal is sampled every 250ms or less,
instead of 32ms.
2. A full SafetySignal status is sampled every 30s or less,
instead of every 32ms.
The SafetySignal impedance is interpreted according to
Table 4.
Table 4. SafetySignal State Ranges
SafetySignal
RESISTANCE
CHARGE STATUS BITS
DESCRIPTION
0Ω to 500Ω
RES_UR
RES_HOT
BATTERY_PRESENT
Underrange
500Ω to 3kΩ
RES_HOT
Hot
BATTERY_PRESENT
3kΩ to 30kΩ
BATTERY_PRESENT
Ideal
30kΩ to 100kΩ RES_COLD
Cold
BATTERY_PRESENT
Above 100kΩ
RES_OR RES_COLD
Overrange
Note: The underrange detection scheme is a very important feature of the
LTC4100. The RTHA/RSafetySignal divider trip point of 0.333 • VDD (1V) is
well above the 0.047 • VDD (140mV) threshold of a system using a 10k
pull-up. A system using a 10k pull-up would not be able to resolve the
important underrange to hot transition point with a modest 100mV of
ground offset between battery and SafetySignal detection circuitry. Such
offsets are anticipated when charging at normal current levels.
The required values for RTHA and RTHB are shown in
Table 5.
Table 5. SafetySignal External Resistor Values
EXTERNAL RESISTOR
VALUE (Ω)
RTHA
1130 ±1%
RTHB
54.9k ±1%
CSS represents the capacitance between the SafetySignal
and GND. CSS may be added to provide additional noise
immunity from transients in the application. CSS cannot
exceed 1nF if the LTC4100 is to properly sense the value
of RSafetySignal.
4100fc
18
For more information www.linear.com/LTC4100
Share Link: 
