APPLICATION INFORMATION

IN +

IN −

OUT

30 k

Ω

+

−

VCC

1/4 LP2901

IN +

IN −

100 k

Ω

1/4 LP2901

1/4 SN54/74LS00 or

1/4 SN54/74ALS1000A

VCC

+

−

12

3

OUT

VCC

VO

Q2

Q1

Q3

I1 = 6 µA

LP2901-Q1

SLCS148A – SEPTEMBER 2005 – REVISED APRIL 2008................................................................................................................................................ www.ti.com

Figure 1 shows the basic configuration for using the LP2901 comparator. Figure 2 shows the diagram for using it

as a CMOS driver.

Figure 1. Basic Comparator

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 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, the Darlington mode and the 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 typical.

Figure 3. Output-Section Schematic Diagram

4

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