8.3 Feature Description

Each channel of the ULN2003A device consists of Darlington connected NPN transistors. This connection

creates the effect of a single transistor with a very high-current gain (β2). This can be as high as 10,000 A/A

at certain currents. The very high β allows for high-output current drive with a very low input current, essentially

equating to operation with low GPIO voltages.

The GPIO voltage is converted to base current through the 2.7-kΩ resistor connected between the input and

base of the predriver Darlington NPN. The 7.2-kΩ and 3-kΩ resistors connected between the base and emitter of

each respective NPN act as pulldowns and suppress the amount of leakage that may occur from the input.

The diodes connected between the output and COM pin is used to suppress the kick-back voltage from an

inductive load that is excited when the NPN drivers are turned off (stop sinking) and the stored energy in the

coils causes a reverse current to flow into the coil supply through the kick-back diode.

In normal operation the diodes on base and collector pins to emitter will be reversed biased. If these diodes are

forward biased, internal parasitic NPN transistors will draw (a nearly equal) current from other (nearby) device

pins.

8.4 Device Functional Modes

8.4.1 Inductive Load Drive

When the COM pin is tied to the coil supply voltage, ULN2003A device is able to drive inductive loads and

suppress the kick-back voltage through the internal free-wheeling diodes.

8.4.2 Resistive Load Drive

When driving a resistive load, a pullup resistor is needed in order for ULN2003A device to sink current and for

there to be a logic high level. The COM pin can be left floating for these applications.

www.ti.com

ULN2002A, ULN2003A, ULN2003AI

ULQ2003A, ULN2004A, ULQ2004A

SLRS027Q – DECEMBER 1976 – REVISED JULY 2022

Copyright © 2022 Texas Instruments Incorporated

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Product Folder Links: ULN2002A ULN2003A ULN2003AI ULQ2003A ULN2004A ULQ2004A