TPS24711DGSR【PDF 16/34 页】IC CTRLR HOT SWAP 2.5-18V 10MSOP

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Sheet目录47

12页 13页 14页 15页 [16页]17页 18页 19页 20页

_IN:InputCurrent,2 A/div

AT:VoltageonGATEPin,5V/div

_DS:Drain-to-SourceVoltageofM1,5V/div

IMER:Voltageon TIMERPin,500mV/div

ET_PWR:PoweronM1(productofV_DSandI_IN),19W/div

ime:10ms/div

TPS24710,TPS24711

TPS24712,TPS24713

SLVSAL2E JANUARY 2011REVISED NOVEMBER 2013

www.ti.com

dissipated within the MOSFET, labeled FET PWR, remaining substantially constant during this period of

operation, which ends when the current through the MOSFET reaches the current limit I

LIM

. This behavior can be

considered a form of foldback limiting, but unlike the standard linear form of foldback limiting, it allows the power

device to operate near its maximum capability, thus reducing the start-up time and minimizing the size of the

required MOSFET.

Figure 27. Computation of M

Power Stress During Start-Up

CIRCUIT BREAKER AND FAST TRIP

The TPS24710/11/12/13 monitors load current by sensing the voltage across R

SENSE

. The TPS24710/11/12/13

incorporates two distinct thresholds: a current-limit threshold and a fast-trip threshold.

The functions of circuit breaker and fast-trip turn off are shown in Figure 28 through Figure 31.

Figure 28 shows the behavior of the TPS24710/11 when a fault in the output load causes the current passing

through R

SENSE

to increase to a value above the current limit but less than the fast-trip threshold. When the

current exceeds the current-limit threshold, a current of approximately 10 糀 begins to charge timing capacitor

. If the voltage on C

reaches 1.35 V, then the external MOSFET is turned off. The TPS24710 latches off and

the TPS24711 commences a restart cycle. In either event, fault pin FLTb pulls low to signal a fault condition.

Overload between the current limit and the fast trip threshold is permitted for this period. This shutdown scheme

is sometimes called an electronic circuit breaker.

The fast-trip threshold protects the system against a severe overload or a dead short circuit. When the voltage

across the sense resistor R

SENSE

exceeds the 60 mV fast-trip threshold, the GATE pin immediately pulls the

external MOSFET gate to ground with approximately 1 A of current. This extremely rapid shutdown may

generate disruptive transients in the system, in which case a low-value resistor inserted between the GATE pin

and the MOSFET gate can be used to moderate the turn off current. The fast-trip circuit holds the MOSFET off

for only a few microseconds, after which the TPS24710/11/12/13 turns back on slowly, allowing the current-limit

feedback loop to take over the gate control of M

. Then the hot-swap circuit goes into either latch mode

(TPS24710/12) or auto-retry mode (TPS24711/13). Figure 30 and Figure 31 illustrate the behavior of the system

implementing TPS24710/11 when the current exceeds the fast-trip threshold.

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