LP2901-Q1_14 Datasheet, PDF (4/10 Pages) Texas Instruments – LOW-POWER QUAD DIFFERENTIAL COMPARATOR

LP2901-Q1
SLCS148A – SEPTEMBER 2005 – REVISED APRIL 2008................................................................................................................................................ www.ti.com
APPLICATION INFORMATION
Figure 1 shows the basic configuration for using the LP2901 comparator. Figure 2 shows the diagram for using it
as a CMOS driver.
V_CC
V_CC
30 kΩ
IN +
+
IN −
−
OUT
1/4 LP2901
Figure 1. Basic Comparator
100 kΩ
IN +
+
3
IN −
−
12
OUT
1/4 LP2901
1/4 SN54/74LS00 or
1/4 SN54/74ALS1000A
Figure 2. CMOS Driver
All pins of any unused comparators should be grounded. The bias network of the LP2901 establishes a drain
current that is independent of the magnitude of the power-supply voltage over the range of 2 V to 30 V. It usually
is necessary to use a bypass capacitor across the power-supply line.
The differential input voltage may be larger than V_CC without damaging the device. Protection should be provided
to prevent the input voltages from going negative by more than –0.3 V. The output section has two distinct
modes of operation, the Darlington mode and the ground-emitter mode. This unique drive circuit permits the
device to sink 30 mA at V_O = 2 V in the Darlington mode and 700 µA at V_O = 0.4 V in the ground-emitter mode.
Figure 3 is a simplified schematic diagram of the output section. The output section is configured in a Darlington
connection (ignoring Q3). If the output voltage is held high enough (above 1 V), Q1 is not saturated and the
output current is limited only by the product of the h_FE of Q1, the h_FE of Q2, and I₁ and the 60-Ω saturation
resistance of Q2. The devices are capable of driving LEDs, relays, etc. in this mode while maintaining an
ultra-low power-supply current of 60 µA typical.
V_CC
I₁ = 6 µA
Q3
V_O
Q1
Q2
Figure 3. Output-Section Schematic Diagram
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