The LP239 is obsolete

and is no longer supplied.

LP239, LP339, LP2901

LOW POWER QUAD DIFFERENTIAL COMPARATORS

SLCS004B − OCTOBER 1987 − REVISED SEPTEMBER 2004

4

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

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.

Figure 1. Basic Comparator

IN +

IN −

OUT

30 k

Ω

+

−

VCC

1/4 LP239, LP339,

or LP2901

Figure 2. CMOS Driver

IN +

IN −

100 k

Ω

1/4 LP239, LP339,

or LP2901

1/4 SN54/74LS00 or

1/4 SN54/74ALS1000A

VCC

+

−

12

3

OUT

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 usually is necessary to use a bypass capacitor across the power supply line.

The differential input voltage may be larger than VCC 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 ground-emitter mode. This unique drive circuit permits the

device to sink 30 mA at VO = 2 V in the Darlington mode and 700 µA at VO = 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 hFE of Q1, the hFE 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, typically.

VCC

VO

Q2

Q1

Q3

I1 = 6

µA

Figure 3. Output-Section Schematic Diagram