TPS2359RHHT datasheet(39/51 Pages) TI

39 / 51 page

Internal Bleed-Down Resistors and Bleed-Down Thresholds

Fault Timer Programming

0 01

fault

(8)

TPS2359

www.ti.com ................................................................................................................................................... SLUS792D – FEBRUARY 2008 – REVISED JUNE 2008

The TPS2359 includes two features intended to support downstream loads that require removal and

reapplication of power to properly reset their internal circuitry. Disabling and re-enabling a channel of the

TPS2359 will not necessarily reset such a load because the capacitance attached to the output bus may not fully

discharge.

The TPS2359 includes four bleed down comparators that monitor the output rails through pins OUT12A,

OUT12B, OUT3A, and OUT3B. The I2C interface includes four bits that enable these comparators — 3ADS,

3BDS, 12ADS, and 12BDS. Enabling a bleed down comparator prevents its corresponding channel from turning

on until the output voltage drops below about 100 mV. This precaution ensures that the output rail drops so low

that all downstream loads properly reset.

In case the downstream load cannot quickly bleed off charge from the output capacitance, the TPS2359 also

includes bleed down resistors connected to each output rail through pins OUT12A, OUT12B, OUT3A, and

OUT3B. Internal switches connect these resistors from their corresponding rails to ground when the channels are

disabled, providing that one sets the appropriate bits in the I2C interface. These bits are named 12AUV, 12BUV,

3AUV, and 3BUV. Clearing these bits ensures that the corresponding resistors never connect to their buses.

If redundant supplies connect to an output, then one should clear the corresponding bleed-down threshold and

bleed-down resistor bits. Failing to clear the bleed-down threshold bit will prevent the channel from enabling so

long as the redundant supply continues to hold up the output rail. Failing to clear the bleed-down resistor bit will

cause current to continually flow through the resistor when the TPS2359 is disabled and the redundant supply

holds up the output bus.

Each of the TPS2359's four channels includes a fault timer. This timer begins operating whenever the channel

enters current limit. If the channel remains in current limit so long that the fault timer runs out, then the channel

turns off the pass FET and reports a fault condition by means of the xFLT bit in the I2C interface.

The four fault timers are independently programmable from 0.5 to 16 ms in steps of 0.5 ms using the appropriate

xFT bits. A code of xFT = 00001B corresponds to the minimum programmable time of 0.5 ms. The code xFT =

00000B corresponds to an extremely short time interval of no practical use.

The locations of the fault timer programming bits are:

Table 16. Fault Time Control Bits

CHANNEL

8 ms

4 ms

2 ms

1 ms

0.5 ms

12A

R1[4]

R1[3]

R1[2]

R1[1]

R1[0]

12B

R4[4]

R4[3]

R4[2]

R4[1]

R4[0]

R2[4]

R2[3]

R2[2]

R2[1]

R2[0]

R5[4]

R5[3]

R5[2]

R5[1]

R5[0]

The user should select the shortest fault times sufficient to allow down-stream loads and bulk capacitors to

charge. Shorter fault times reduce the stresses imposed on the pass FETs under fault conditions. This

consideration may allow the use of smaller and less expensive pass FETs for the 12-V channels.

The TPS2359 supports two modes of fault timer operation. Clearing the FLTMODE bit causes a channel to latch

off whenever its fault timer runs out. The channel remains off until it has been disabled and re-enabled (see

Enable Functions section). The TPS2359 operates in this manner by default. Setting the FLTMODE bit causes a

faulted channel to automatically attempt to turn back on after a delay roughly one hundred times the fault time.

This process repeats until either the fault disappears or the user disables the channel. The pass FET for a 12-V

channel with a shorted output must therefore continuously dissipate

where VIN12x equals the voltage present at the input of the 12-V channel and ICL equals the current limit setting

for this channel (the inrush current if 12VNRS is set).

Submit Documentation Feedback

Product Folder Link(s): TPS2359

TPS2359RHHT Datasheet(PDF) 39 Page - Texas Instruments

TPS2359RHHT Datasheet(HTML) 39 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

Datasheet Download

Link URL