UCC2913 datasheet(7/17 Pages) TI

7 / 17 page

UCC2913

UCC3913

SLUS274A – JANUARY 1999 – REVISED APRIL 2003

www.ti.com

APPLICATION INFORMATION

During a fault, CT charges at a rate determined by the internal charging current and the external timing capacitor.

Once CT charges to 2.5 V, the fault comparator switches and sets the fault latch. Setting of the fault latch causes

both the output to switch off and the charging switch to open. CT must now discharge with the 1-µA current

source, I2, until 0.5 V is reached. Once the voltage at CT reaches 0.5 V, the fault latch resets, which re-enables

the output and allows the fault circuitry to regain control of the charging switch. If a fault is still present, the fault

comparator closes the charging switch causing the cycle to begin. Under a constant fault, the duty cycle is given

by:

Duty Cycle

PL ) 36 mA

Average power dissipation in the pass element is given by:

FET(avg) + VFET

IMAX

PL ) 36 mA

Where VFET >> 5 V IPL can be approximated as :

PL ^

FET

and where IPL >> 36 µA, the duty cycle can be approximated as :

Duty Cycle

FET

Therefore, the maximum average power dissipation in the MOSFET can be approximated by:

FET(avg) + VFET

IMAX

FET

+ IMAX

Notice that in the approximation, VFET cancels. therefore, average power dissipation is limited in the N-channel

MOSFET pass element.

Overload Comparator

The linear amplifier in the UCCx913 ensures that the output N-channel MOSFET does not pass more than IMAX

(which is VIMAX/RS). In the event the output current exceeds the programmed IMAX by 0.2 V/RS (which can only

occur if the output MOSFET is not responding to a command from the device) the CT pin begins charging with

I3, 1 mA, and continue to charge to approximately 8 V. This allows a constant fault to show up on the SD/FLT

pin, and also since the voltage on CT charges past 2.5 V only in an overload fault mode, it can be used for

detection of output FET failure or to build in redundancy in the system.

(6)

(7)

(8)

(9)

(10)

UCC2913 Datasheet(PDF) 7 Page - Texas Instruments

UCC2913 Datasheet(HTML) 7 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Datasheet Download

Link URL