UCC1921 datasheet(2/11 Pages) TI

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UCC1921

UCC2921

UCC3921

ELECTRICAL CHARACTERISTICS Unless otherwise specified, TA = 0°C to 70°C for the UCC3921 and –40°C to 85°C

for the UCC2921, and –55°C to 125°C for the UCC1921; IVDD = 2mA, CT = 1nF (the minimum allowable value), there is no

resistor connected between the SDFLTCH and VSS pins. TA =TJ.

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

VDD Section

IDD

Regulator Voltage

ISOURCE = 2mA

9.5

10.0

ISOURCE = 10mA

9.15

9.6

10.15

UVLO Off Voltage

Fault Timing Section

Overcurrent Threshold

TJ = 25°C

47.5

53.5

Over Operating Temperature

53.5

Overcurrent Input Bias

500

CT Charge Current

VCT = 1V, IPL = 0

–50

–36

–22

µA

Overload Condition, VSENSE -VIMAX = 300mV

–1.7

–1.2

–0.7

CT Discharge Current

VCT = 1V, IPL = 0

0.6

1.5

µA

CT Fault Threshold

2.2

2.45

2.6

CT Reset Threshold

0.41

0.49

0.57

Output Duty Cycle

Fault Condition, IPL = 0

1.7

2.7

3.7

CONNECTION DIAGRAM

DIL-8 , SOIC-8 (Top View)

NorJ, D Packages

ABSOLUTE MAXIMUM RATINGS

IVDD.......................................... 50mA

SDFLTCH Current .............................. 10mA

PL Current .................................... 10mA

IMAX Input Voltage ..............................VDD

Storage Temperature ...................

−65°C to +150°C

Junction Temperature ................... –55°C to +150°C

Lead Temperature (Soldering, 10 sec.) ............. +300°C

All voltages are with respect to VSS (the most negative voltage).

Currents are positive into, negative out of the specified terminal.

Consult Packaging Section of Databook for thermal limitations and

considerations of packages.

dropout. The fault current level is set with an external

current sense resistor, while the maximum allowable

sourcing current is programmed with a voltage divider

from VDD to generate a fixed voltage on IMAX. The cur-

rent level, when the output acts as a current source, is

equal to VIMAX/RSENSE. If desired, a controlled current

start up can be programmed with a capacitor on IMAX.

When the output current is below the fault level, the out-

put device is switched on. When the output current ex-

ceeds the fault level, but is less than the maximum

sourcing level programmed by IMAX, the output remains

switched on, and the fault timer starts charging CT. Once

CT charges to 2.5V, the output device is turned off and

performs a retry some time later (provided that the se-

lected mode of operation is Automatic Retry Mode).

When the output current reaches the maximum sourcing

current level, the output acts as a current source, limiting

the output current to the set value defined by IMAX.

Other features of the UCC3921 include undervoltage

lockout, 8-pin Small Outline (SOIC) and Dual-In-Line

(DIL) packages, and a Latched Operation Mode option,

in which the output is latched off once CT charges to

2.5V and stays off until either SDFLTCH is toggled (for

greater than 1ms) or the IC is powered down and then

back up.

DESCRIPTION (continued)

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