LTC3577EUFF-4 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC3577EUFF-4' PDF : 52 Pages View PDF
LTC3577-3/LTC3577-4
OPERATION
In the explanation below, the following notation is used.
R25 = Value of the thermistor at 25°C
RNTC|COLD = Value of thermistor at the cold trip point
RNTC|HOT = Value of the thermistor at the hot trip point
rCOLD = Ratio of RNTC|COLD to R25
rHOT = Ratio of RNTC|HOT to R25
RNOM = Primary thermistor bias resistor (see Figure 3)
R1 = Optional temperature range adjustment resistor
(see Figure 4)
The trip points for the LTC3577-3/LTC3577-4’s temperature
qualification are internally programmed at 0.35 • VNTC for
the hot threshold and 0.76 • VNTC for the cold threshold.
Therefore, the hot trip point is set when:
RNTC|HOT • NTCBIAS = 0.35 • NTCBIAS
RNOM + RNTC|HOT
and the cold trip point is set when:
RNTC|COLD • NTCBIAS = 0.76 • NTCBIAS
RNOM + RNTC|COLD
Solving these equations for RNTC|COLD and RNTC|HOT results
in the following:
RNTC|HOT = 0.538 • RNOM
and
RNTC|COLD = 3.17 • RNOM
By setting RNOM equal to R25, the above equations result
in rHOT = 0.538 and rCOLD = 3.17. Referencing these ratios
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.
NTCBIAS
34
RNOM
100k
NTC
35
NTC BLOCK
0.76 • NTCBIAS
–
+
RNTC
100k
–
0.35 • NTCBIAS
+
LTC3577-3/
LTC3577-4
TOO_COLD
TOO_HOT
0.26 • NTCBIAS
+
–
BATTERY
OVERTEMP
357734 F03
Figure 3. Typical NTC Thermistor Circuit
NTCBIAS
34
RNOM
105k
NTC
35
R1
12.7k
RNTC
100k
NTC BLOCK
0.76 • NTCBIAS
–
+
–
0.35 • NTCBIAS
+
LTC3577-3/
LTC3577-4
TOO_COLD
TOO_HOT
0.26 • NTCBIAS
+
–
BATTERY
OVERTEMP
357734 F04
Figure 4. NTC Thermistor Circuit with Additional Bias Resistor
26
357734fb
Share Link: 
