LTC3577EUFF#PBF Linear Technology, LTC3577EUFF#PBF Datasheet - Page 28

• Manufacturer Part Number: LTC3577EUFF#PBF
• Description: IC PWR MANAGEMENT HANDHELD 44QFN
• Manufacturer: Linear Technology

Specifications of LTC3577EUFF#PBF

• Applications: Handheld/Mobile Devices
• Voltage - Supply: 4.35 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 44-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -

OPERATION
LTC3577/LTC3577-1
temperature falls back below the discharge temperature
threshold. The battery discharge circuitry is only enabled
if the battery voltage is greater than the battery discharge
threshold.
Alternate NTC Thermistors and Biasing
The LTC3577 provides temperature qualifi ed charging if
a grounded thermistor and a bias resistor are connected
to NTC. By using a bias resistor whose value is equal to
the room temperature resistance of the thermistor (R25)
the upper and lower temperatures are pre-programmed
to approximately 40°C and 0°C, respectively (assuming
a Vishay “Curve 1” thermistor).
The upper and lower temperature thresholds can be ad-
justed by either a modifi cation of the bias resistor value
or by adding a second adjustment resistor to the circuit.
If only the bias resistor is adjusted, then either the upper
or the lower threshold can be modifi ed but not both. The
other trip point will be determined by the characteristics
of the thermistor. Using the bias resistor in addition to an
adjustment resistor, both the upper and the lower tempera-
ture trip points can be independently programmed with
the constraint that the difference between the upper and
lower temperature thresholds cannot decrease. Examples
of each technique follows.
NTC thermistors have temperature characteristics which
are indicated on resistance-temperature conversion tables.
The Vishay-Dale thermistor NTHS0603N011-N1003F , used
in the following examples, has a nominal value of 100k
and follows the Vishay “Curve 1” resistance-temperature
characteristic.
In the following explanation, this notation is used.
28
R25 = Value of the thermistor at 25°C
R
R
r
r
R
R1 = Optional temperature range adjustment resistor
(see Figure 9)
COLD
HOT
NTC|COLD
NTC|HOT
NOM
= Ratio of R
= Primary thermistor bias resistor (see Figure 9)
= Ratio of R
= Value of the thermistor at the hot trip point
= Value of thermistor at the cold trip point
NTC|HOT
NTC|COLD
to R25
to R25
The trip points for the LTC3577’s temperature qualifi ca-
tion are internally programmed at 0.35 • V
threshold and 0.76 • V
Therefore, the hot trip point is set when:
and the cold trip point is set when:
Solving these equations for R
in the following:
and
By setting R
in r
to the Vishay Resistance-Temperature Curve 1 chart gives
a hot trip point of about 40°C and a cold trip point of about
0°C. The difference between the hot and cold trip points
is approximately 40°C.
Figure 9. NTC Thermistor Circuit with Additional Bias Resistor
R
R
R
R
HOT
NTC|HOT
NTC|COLD
NOM
NOM
NTCBIAS
R
105k
R1
12.7k
R
100k
NOM
NTC
= 0.538 and r
R
R
34
35
NTC
NTC|HOT
NTC|COLD
+ R
+ R
NOM
= 0.538 • R
NTC|HOT
NTC|COLD
= 3.17 • R
0.35 • NTCBIAS
0.26 • NTCBIAS
0.76 • NTCBIAS
equal to R25, the above equations result
COLD
• NTCBIAS = 0.35 • NTCBIAS
• NTCBIAS = 0.76 • NTCBIAS
NTC
NOM
NOM
= 3.17. Referencing these ratios
for the cold threshold.
NTC|COLD
–
–
–
NTC BLOCK
+
+
+
and R
NTC
NTC|HOT
TOO_COLD
TOO_HOT
BATTERY
OVERTEMP
LTC3577
for the hot
3577 F09
results
3577fa