LM57B10EB/NOPB National Semiconductor, LM57B10EB/NOPB Datasheet - Page 3

• Manufacturer Part Number: LM57B10EB/NOPB
• Description: Temperature Switch/Sensor Eval. Board
• Manufacturer: National Semiconductor

Specifications of LM57B10EB/NOPB

• Silicon Manufacturer: National
• Application Sub Type: Temperature Sensor
• Kit Application Type: Sensing - Temperature
• Silicon Core Number: LM57
• Kit Contents: Board And Literature

Supply Current
One of the biggest concerns for system designers today is
system power consumption. The LM57 has extremely low
power consumption compared to an NTC-based discrete cir-
cuit. Figure 4 shows the typical current consumption of three
circuits: LM57, a 100 kΩ NTC thermistor discrete circuit, and
a 10 kΩ NTC thermistor discrete circuit.
When calculating the supply current of the discrete circuits,
the sum of the supply currents for the thermistor, comparator,
and two voltage references was calculated. Note that a very
low-power comparator (LMV7271) and two low-power refer-
ences (LM4128) were used in the calculations; these compo-
FIGURE 3. Functional Block Diagram of LM57 Integrated
Analog Temperature Sensor and Temperature Switch
3
nents contributed only 129 µA of supply current for devices
other than the NTC. The majority of the current consumption
in this simulation is due to the NTC and its bias resistor. As
temperature increases, the thermistor resistance decreases,
causing much greater current draw for the circuit. In the case
of the 10 kΩ thermistor circuit, the supply current reaches 437
µA at 125°C.
By contrast, the LM57 consumes a mere 24 µA of supply cur-
rent over its full operating range of −50°C to 150°C. The
integrated sensor uses a low-power CMOS band-gap sensor,
which provides significant power savings over thermal-resis-
tive circuits.
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