LTC4110EUHF LINER [Linear Technology], LTC4110EUHF Datasheet - Page 25

• Manufacturer Part Number: LTC4110EUHF
• Description: Battery Backup System Manager
• Manufacturer: LINER [Linear Technology]

OPERATION
Where:
For Example, if we charge a 3Ah battery with 1A current,
then x = 15.
SAFETYSIGNAL DECODER
Table 3. SafetySignal State Ranges (Except SLA)
SafetySignal
CHARGE
RESISTANCE
0Ω to 500Ω
500Ω to 3k
3kΩ to 30k
30k to 100k
Above 100k
Note: The under range detection scheme is a very important feature of the
LTC4110. The R
is well above the 0.047 • V
pull-up. A system using a 10k pull-up would not be able to resolve the
important under range to a 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.
Table 4. SafetySignal for SLA (7.256k Between THA and THB)
SafetySignal
CHARGE
RESISTANCE
0Ω to 3.1k
3.1k to 114k
114k
This decoder measures the resistance of the SafetySignal
and features high noise immunity at critical trip points.
The SafetySignal decoder is shown in Figure 10.
The value of R
sensing is accomplished by a state machine that reconfi gures
the switches of Figure 10 using THA_SELB and THB_SELB,
a selectable reference generator, and two comparators.
The state machine successively samples the SafetySignal
value starting with the RES_OR ≥ RES_COLD threshold,
C = C rate of the battery
I
CHG
= Programmed charging current
THA
THA
/R
SafetySignal
RES_UR, RES_HOT,
BATTERY_PRESENT
RES_HOT, BATTERY_PRESENT
BATTERY_PRESENT
RES_COLD, BATTERY_PRESENT
RES_OR, RES_COLD
is 1.13k and R
CHARGE STATUS BITS
DD
CHARGE STATUS BITS
RES_HOT,
BATTERY_PRESENT
BATTERY_PRESENT
RES_COLD, RES_OR
= 140mV threshold of a system using a 10k
divider trip point of 0.307 • 4.75V = 1.46V
THB
is 54.9k. SafetySignal
Battery Removal
DESCRIPTION
DESCRIPTION
Under range
Overrange
Ideal
Hot
Ideal
Cold
Hot
then RES_C0LD ≥ RES_IDEAL threshold, RES_IDEAL ≥
RES_HOT threshold, and fi nally 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 R
the RES_OR ≥ RES_COLD and RES_COLD ≥ RES_IDEAL
thresholds by connecting the THB pin to an internal voltage
and measuring the voltage resultant on the THA pin. The
R
RES_HOT and RES_HOT ≥ RES_UR thresholds by con-
necting the THA pin to the internal voltage and measuring
the resultant voltage on the THB pin. The SafetySignal
impedance is interpreted according to Table 3.
When the DCIN supply is present, a full sampling of the
SafetySignal is performed every 27ms. When the supply is
absent, a low power limited sampling of the SafetySignal is
performed every 218ms. A full sampling of the thermistor
state is performed only if a change of battery presence is
detected when the supply is not present.
GPIO AND STATUS FUNCTIONS
All of the GPIO pins are open drain with N-MOSFET drivers
capable of sinking current suffi cient to drive an LED (see
V
instead enter a Hi-Z mode when the output is not low. An
external pull-up will be required to create any high output
logic state.
THA
OL
C
SS
). The pins are not capable of sourcing any current and
resistor value is used to measure the RES_IDEAL ≥
Figure 10. Battery Safety Decoder (Except SLA)
R
1.13k
54.9k
R
R
SafetySignal
THA
THB
THA
THB
V
V
INT
INT
THB
THA_SELB
THB_SELB
resistor value is used to measure
SafetySignal
CONTROL
LATCH
MUX
REF LO_REF
HI_REF
RES_OR
RES_COLD
RES_HOT
RES_UR
LTC4110
+
–
+
–
25
TH_HI
TH_LO
4110fa
4110 F10