Datasheet

V
OUT
= 2.5 x (R2 + R3)/R3
= 2.5 x (3k + 3k)/3k = 5V
V+
V
SUPPLY
C1
10 PF
LMV7231
C2
0.1 PF
R1
100
V+ = 3.3V
R1
R2
V
BATT
V
OUT
499k
1M
+
-
R3
3.01k
LMV7231
SNOSB45E –FEBRUARY 2010–REVISED MARCH 2013 www.ti.com
The supply independent inputs of the window comparator blocks allow the LMV7231 to be tolerant of system
faults. For example if the power is suddenly removed from the LMV7231 due to a system malfunction yet there
still exists a voltage on the input, this will not be an issue as long as the monitored input voltage does not exceed
absolute maximum ratings. Another example where this feature comes in handy is a battery sense application
such as the one in Figure 38. The boards may be sitting on the shelf unbiased with V+ grounded, and yet have a
fully charged battery on board. If the comparator measuring the battery had crowbar diodes, the diode from –IN
to V+ would turn on, sourcing current from the battery eventually draining the battery. However, when using the
LMV7231 no current, except the low input bias current of the device, will flow into the chip, and the battery
charge will be preserved.
Figure 38. Battery Sense Application
The output pin voltages of the device can also exceed the supply voltage, V+, of the comparator. This provides
extra flexibility and enables designs which pull up the outputs to higher voltage levels to meet system
requirements. For example it’s possible to run the LMV7231 at its minimum operating voltage, V+ = +2.2V, but
pull up the output up to the absolute maximum ratings to bias a blue LED, with a forward voltage of V
F
= +4V.
In a power supply supervision application the hardwired LMV7231 is a sound solution compared to the uC with
software alternative for several reasons. First, startup is faster. During startup you don’t need to account for code
loading time, oscillator ramp time, and reset time. Second, operation is quick. The LMV7231 has a maximum
propagation delay in the µs and isn’t affected by sampling and conversion delays related to reading data,
calculating data, and setting flags. Third, less overhead. The LMV7231 doesn’t require an expensive power
consuming microcontroller nor is it dependent on controller code which could get damaged or crash.
POWER SUPPLY BYPASSING
Bypass the supply pin, V+, with a 0.1 μF ceramic capacitor placed close to the V+ pin. If transients with rise/fall
times of 100’s μs and magnitudes of 100’s mV are expected on the power supply line a RC low pass filter
network as shown in Figure 39 is recommended for additional bypassing. If no such bypass network is used
power supply transients can cause the internal voltage reference of the comparator to temporarily shift potentially
resulting in a brief incorrect comparator output. For example if an RC network with 100Ω resistance and 10μF
capacitance (1.1ms rise time) is used the voltage reference will shift temporarily the amount, V
TH
Power Supply
Sensitivity (V
TH
PSS), specified in the Electrical Characteristics table.
Figure 39. Power Supply Bypassing
POWER SUPPLY SUPERVISION
Figure 40 shows a power supply supervision circuit utilizing the LMV7231. This application uses the efficient,
easy to use LM25007 step-down switching regulator. This switching regulator can handle a 9V – 42V input
voltage range and it’s regulated output voltage is set to 5V with R2 = R3 = 3kΩ.
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