UCC2913 datasheet(6/9 Pages) TI

6 / 9 page

UCC1913

UCC2913

UCC3913

µAR

FET

•

Therefore, the maximum average power dissipation in

the MOSFET can be approximated by:

VIMAX

IMAX

A R

FET avg

FET

() =

••

•

=•

•

Notice that in the approximation, VFET cancels. therefore,

average power dissipation is limited in the NMOS pass

element.

Overload Comparator

The linear amplifier in the UCC1913 ensures that the

output NMOS does not pass more than IMAX (which is

VIMAX/RS). In the event the output current exceeds the

programmed IMAX by 0.2V/RS, which can only occur if

the output FET is not responding to a command from the

IC, the CT pin will begin charging with I3, 1mA, and con-

tinue to charge to approximately 8V. This allows a con-

stant fault to show up on the SD/FLT pin, and also since

the voltage on CT will only charge past 2.5V in an over-

load fault mode, it can be used for detection of output

FET failure or to build in redundancy in the system.

Determining External Component Values

Referring now to Figure 3. To set RVDD the following

must be achieved:

()

VDD

min

In order to estimate the minimum timing capacitor, CT,

several things must be taken into account. For example,

given the schematic below as a possible (and at this

point, a standard) application, certain external compo-

nent values must be known in order to estimate CT(min).

Now, given the values of COUT, Load, RSENSE, VSS, and

the resistors determining the voltage on the IMAX pin,

the user can calculate the approximate startup time of

the node VOUT. This startup time must be faster than the

time it takes for CT to charge to 2.5V (relative to VSS),

and is the basis for estimating the minimum value of CT.

In order to determine the value of the sense resistor,

RSENSE, assuming the user has determined the fault cur-

rent, RSENSE can be calculated by:

SENSE

FAULT

APPLICATION INFORMATION (cont.)

Figure 3.

∞

Figure 4. Plot average power vs. FET voltage for

increasing values of RPL.

SHUTDOWN

SD/FLT

VSS

LEVEL SHIFT

LOCAL VDD

LOCAL GND

FAULT OUT

Figure 5. Possible level shift circuitry to interface to

the UCC1913.

UCC2913 数据表(PDF) 6 Page - Texas Instruments

UCC2913 数据表(HTML) 6 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9

数据表下载