LTC1759 Ver la hoja de datos (PDF) - Linear Technology
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LTC1759 Datasheet PDF : 28 Pages
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LTC1759
U
OPERATIO
When AC power is not available the thermistor block
supports the following low power operating features:
1. Only the low power THERM_OR detection circuitry is
kept alive to support battery present interrupts.
2. The ChargeStatus() read function forces the thermistor
block to update thermistor status at the beginning of the
read. The low power mode is immediately reentered
upon completion of the read.
The thermistor impedance is interpreted according to
Table 4.
Table 4. Thermistor State Ranges
THERMISTOR
RESISTANCE
CHARGE
STATUS BITS
0Ω to 500Ω
THERM_UR,
THERM_HOT
BATTERY_PRESENT
500Ω to 3kΩ
THERM_HOT
BATTERY_PRESENT
3kΩ to 30kΩ
(NONE)
BATTERY_PRESENT
30kΩ to 100kΩ
THERM_COLD
BATTERY_PRESENT
Above 100kΩ
THERM_OR
THERM_COLD
DESCRIPTION
Underrange
Hot
Ideal
Cold
Overrange
The required values for RWEAK, RUR and RNR are shown in
Table 5.
Table 5. Thermistor External Resistor Values
EXTERNAL RESISTOR
VALUE (Ω)
RWEAK
475k ±1%
RUR
1k ±1%
RNR
10k ±1%
Note: The maximum allowed total external capacitance on THERM and
RNR is 75pF, due to settling time requirements.
The ILIMIT Decoder Block
The value of an external resistor connected from this pin
to GND determines one of four current limits that are used
to limit the maximum charging current value. These limits
provide a measure of safety with a hardware restriction on
charging current which cannot be overridden by software.
Table 6. ILIMIT Trip Points and Ranges
EXTERNAL
NOMINAL
RESISTOR
(RILIMIT)
CHARGING
ILIMIT VOLTAGE CURRENT RANGE GRANULARITY
0
VILIMIT < 0.09VDD 0 < I < 1023mA
1mA
10k ±1%
0.17VVDD < VILIMIT 0 < I < 2046mA
2mA
< 0.34VVDD
33k ±1%
0.42VVDD < VILIMIT 0 < I < 4092mA
4mA
< 0.59V
Open (>250k, 0.66VVDD < VILIMIT 0 < I < 8184mA
8mA
or Short to
VDD)
VDD
AC_PRESENT
12.5k
+
33k
–
25k
+
4
VLIMIT
25k
–
VLIM [3:0]
ENCODER
+
RLIMIT
25k
–
+
12.5k
–
1759 F05
Figure 5. Simplified VLIMIT Circuit Concept (ILIMIT Is Similar)
The VLIMIT Decoder Block
The value of an external resistor connected from this pin
to GND determines one of five voltage limits that are
applied to the charger output value. These limits provide
a measure of safety with a hardware restriction on charg-
ing voltage which cannot be overridden by software.
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