LP239 Datasheet, PDF (4/7 Pages) Texas Instruments – LOW-POWER QUAD DIFFERENTIAL COMPARATORS

LP239, LP339, LP2901
LOW-POWER QUAD DIFFERENTIAL COMPARATORS
SLCS004A – OCTOBER 1987 – REVISED MAY 1988
APPLICATION INFORMATION
Figure 1 shows the basic configuration for using the LP239, LP339, or LP2901 comparator. Figure 2 shows the
diagram for using one of these comparators as a CMOS driver.
VCC
VCC
30 kΩ
IN +
+
IN –
–
OUT
1/4 LP239, LP339,
or LP2901
Figure 1. Basic Comparator
100 kΩ
IN +
+3
IN –
–
12
OUT
1/4 LP239, LP339,
or 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 LP239, LP339, and 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 is usually 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: a Darlington mode and a 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 ultralow
power supply current of 60 µA typically.
I1 = 6 µA
Q3
VCC
VO
Q1
Q2
Figure 3. Output-Section Schematic Diagram
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