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PDF MAX836-MAX837 Data sheet ( Hoja de datos )
| Número de pieza | MAX836-MAX837 | |
| Descripción | 4-Pin Micropower Voltage Monitors | |
| Fabricantes | Maxim Integrated | |
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19-1137; Rev 0; 9/96
4-Pin Micropower Voltage Monitors
_______________General Description
The MAX836/MAX837 micropower voltage monitors
contain a 1.204V precision bandgap reference and a
comparator in a SOT143 package. The MAX836 has an
open-drain, N-channel output driver, while the MAX837
has a push-pull output driver. Two external resistors set
the trip threshold voltage.
____________________________Features
o ±1.25% Precision Voltage Threshold
o SOT143 Package
o Low Cost
o <5µA Typical Supply Current
o Open-Drain Output (MAX836)
Push-Pull Output (MAX837)
________________________Applications
Precision Battery Monitor
Load Switching
Battery-Powered Systems
Threshold Detectors
______________Ordering Information
PART*
TEMP. RANGE
PIN- MARKING
PACKAGE CODE
MAX836EUS-T -40°C to +85°C 4 SOT143
MAX837EUS-T -40°C to +85°C 4 SOT143
AAEQ
AAER
*All devices available in tape-and-reel only. Contact factory for
availability.
__________Typical Operating Circuit
VCC
GND
1.204V
REF
MAX836
ONLY
OUT
VCC VCC
MAX836
MAX837
IN
0.1µF
__________________Pin Configuration
TOP VIEW
GND 1
MAX836
MAX837
4 OUT
VCC 2
3 IN
SOT-143
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
1 page  
4-Pin Micropower Voltage Monitors
both parts. For the MAX836, select the ratio of resistors
R1 and R2 so that IN sees 1.204V when the monitor
voltage falls to or rises above the desired trip point
(VTRIP). R3 adds hysteresis and is typically an order of
magnitude larger than R1 or R2. The current through R1
and R2 should be at least 500nA to ensure that the
12nA maximum input current does not shift the trip
point significantly. Capacitor C1 adds additional noise
rejection.
Monitoring Voltages Other than VCC
The MAX836/MAX837 can monitor voltages other than
VCC (Figure 3). Calculate VTRIP as shown in the section
Programming the Trip Voltage. The monitored voltage
(VMON) is independent of VCC. VIN must be 1V less
than VCC.
Heater Temperature Control
Figure 4 shows a basic heater temperature-control cir-
cuit. Upon power-up, OUT is high and the N-channel
MOSFET turns on. Current flows through the heating
element (R4), warming the surrounding area. R2 is a
negative-temperature-coefficient thermistor and as tem-
perature increases, its resistance decreases. As the
thermistor heats up and its resistance decreases, the
MAX837’s voltage at IN decreases until it reaches the
1.204V threshold voltage. At this point, OUT goes low,
turning off the heating element. The thermistor cools
and the voltage at IN rises until it overcomes the
MAX837’s hysteresis (6mV). OUT returns high when this
point is reached, turning on the heating element again.
This cycle repeats as long as power is applied.
Determine the thermistor’s resistance (R2) at the
desired temperature. Then, using R2’s resistance and
half the resistance of R3, calculate R1’s value with the
following formula:
R1
=
(R2
+
R3)
VCC
1.204
- 1
___________________Chip Information
TRANSISTOR COUNT: 54
VCC
0.1µF
GND OUT
MAX837
VCC IN
VMON
R1
R2
Figure 3. Monitoring Voltages Other than VCC
GND OUT
MAX837
VCC VCC
IN
OUT
R3
0.1µF
R1
R2 C1
NOTE: C1 ADDS ADDITIONAL NOISE IMMUNITY
VCC
0.1µF
R1
VCC IN
THERMISTOR
WITH
NEGATIVE
MAX837
COEFFICIENT
R2
T
R3
HEATING
ELEMENT
R4
GND OUT
( )R1 = (R2 + R3) VCC - 1 Ω
1.204
Figure 2. Adding Hysteresis to the Comparator
Figure 4. Heater Temperature Control
_______________________________________________________________________________________ 5
5 Page | ||
| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet MAX836-MAX837.PDF ] | |
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