UCC1921 datasheet(3/11 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

Output Section

Output High Voltage

IOUT = 0mA

8.5

IOUT = –1mA

Output Low Voltage

IOUT = 0mA, VSENSE –VIMAX = 100mV

IOUT = 2mA, VSENSE –VIMAX = 100mV

200

600

Linear Amplifier Section

Sense Control Voltage

VIMAX = 100mV

100

115

VIMAX = 400mV

370

400

430

Input Bias

500

Power Limiting Section

VSENSE Regulator Voltage

IPL =64µA

4.35

4.85

5.35

Duty Cycle Control

IPL =64µA

0.6

1.2

1.7

IPL = 1mA

0.045

0.1

0.17

Overload Section

Delay to Output

Note 1

300

500

Output Sink Current

VSENSE –VIMAX = 300mV

100

Threshold

Relative to IMAX

140

200

260

Shutdown/Fault/Latch Section

Shutdown Threshold

VDD+1

Input Current

VSDFLTCH = 5V

110

250

µA

Filter Delay Time (Delay to Output)

250

500

1000

µs

Fault Output High

9.5

ISDFLTCH = –100µA

8.5

Fault Output Low

010

Output Duty Cycle

Fault Condition, IPL = 0

1.7

2.7

3.7

ISDFLTCH = –100µA, Fault Condition, IPL =0

Note 1: Guaranteed by design. Not 100% tested in production.

PIN DESCRIPTIONS

CT: A capacitor is connected to this pin in order to set

the fault time. The fault time must be longer than the time

to charge external load capacitance. The

fault time is

defined as:

FAULT

•

where ICH =36

µA+IPL, and IPL is the current into the

power limit pin. Once the maximum fault time is reached

the output will shutdown for a time given by:

=•

•

210$

IMAX: This pin programs the maximum allowable

sourcing current. Since VDD is a regulated voltage, a

voltage divider can be derived from VDD to generate the

program level for IMAX. The current level at which the

output appears as a current source is equal to the

voltage on IMAX over the current sense resistor. If

desired, a controlled current start up can be programmed

with a capacitor on IMAX, and a programmed start delay

can be achieved by driving the shutdown with an open

collector/drain device into an RC network.

OUT: This pin provides gate output drive to the MOSFET

pass element.

PL: This feature ensures that the average MOSFET

power dissipation is controlled. A resistor is connected

from this pin to the drain of the NMOS pass element.

When the voltage across the NMOS exceeds 5V, current

will flow into the PL pin which adds to the fault timer

charge current, reducing the duty cycle from the 3%

level. When IPL>>36

µA, then the average MOSFET

power dissipation is given by:

avg IMAX

MOSFET

=• •

•

−

110 $

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