TPS24740 Datasheet, PDF (20/61 Pages) Texas Instruments – 2.5-V to 18-V High Performance Hot Swap and ORing Controller

TPS24740
TPS24741
TPS24742
SLVSCV6A – JANUARY 2015 – REVISED FEBRUARY 2015
Feature Description (continued)
9.3.12 Fault Reporting
TPS 2474x will assert a fault by pulling down on the FLTb pin if any of the following occur:
• Hot Swap MOSFET Shorted Fault ( ENHS = LO, but VIMON > 101 mV)
• Hot Swap timer times out.
• ORing MOSFET Open Fault (ENOR = HI, CP up, but V_AC > 410 mV)
• CP is down for more than 32 ms
• Over Temperature Shut Down (OTSD)
Figure 27 shows the logic for the fault conditions.
Timer Timed Out (TO)
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VIMON > 100 mV
Hotswap_Disabled
FET
Shorted
OR_enabled
CP_up
VAC > 410 mV
FET
Open
Deglitch
3.9 ms Rising
and Falling
Deglitch
3.9 ms Rising
and Falling
OTSD
FLTb
FLT
CP_up
Deglitch
32 ms when rising
Starts as No Fault
Figure 27. Logic for Fault Reporting
9.4 Device Functional Modes
The Hot Swap and ORing section of the TPS2474x are for the most part independent. The only exception is that
the Hot Swap is gated by the charge pump being up. This ensures that the ORing FET is ON before the Hot
Swap turns on to avoid a possible glitch from a fast ORing turn on.
9.4.1 ORing Functional Modes
Figure 28 shows the state machine for the ORing portion of the controller. It has three modes listed below:
• Precharge CP: Here the TPS2474x charges the CP node before beginning regular operation. This state is
entered after POR/UVLO or if the CP voltage falls below 3.7V. Whenever the CP voltage is above 5.5V the
FET OFF state is entered
• FET OFF: In this state the ORing FET is OFF and is pulled down to A with a 35mA current source. If a
forward voltage drop is detected across the FET (V_AC > 10mV) the TPS2474x enters the FET ON state.
There is a 30mA fast pull up that lasts 20µs, followed by a sustained 0.3 mA pull up.
• FET ON: In this state the ORing FET is pulled up to the CP voltage. If reverse current is detected (RVSNP >
RVSNM) the TPS2474x will enter the OFF state. There is a 0.9A pull down current that lasts 15 µs, followed
by a sustained 35mA pull down.
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