TPS24711DGSR【PDF 15/34 页】IC CTRLR HOT SWAP 2.5-18V 10MSOP

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Sheet目录47

11页 12页 13页 14页 [15页]16页 17页 18页 19页

TPS24710,TPS24711

TPS24712,TPS24713

www.ti.com

SLVSAL2E JANUARY 2011REVISED NOVEMBER 2013

Figure 26. Inrush Mode at Hot-Swap Circuit Insertion

INRUSH OPERATION

After TPS24710/11/12/13 initialization is complete (as described in the Board Plug-In section) and EN is active,

GATE is enabled (V

GATE

starts increasing). When V

GATE

reaches the MOSFET M1 gate threshold, a current flows

into the downstream bulk storage capacitors. When this current exceeds the limit set by the power limit engine,

the gate of the MOSFET is regulated by a feedback loop to make the MOSFET current rise in a controlled

manner. This not only limits the inrush current charging capacitance but it also limits the power dissipation of the

MOSFET to safe levels. A more complete explanation of the power limiting scheme is given in the section

entitled Action of the Constant Power Engine. When Gate is enabled, the TIMER pin begins to charge the timing

capacitor C

with a current of approximately 10 糀. The TIMER pin continues to charge C

until V

(GATE VCC)

reaches the timer activation voltage (5.9 V for V

VCC

= 12 V). The TIMER then begins to discharge C

with a

current of approximately 10 糀. This indicates that the inrush mode is finished. If the TIMER exceeds its upper

threshold of 1.35 V before V

(GATE VCC)

reaches the timer activation voltage, the GATE pin is pulled to GND and

the hot-swap circuit enters either latch mode (TPS24710/12) or auto-retry mode (TPS24711/13).

The power limit feature is disabled once the inrush operation is finished and the hotswap circuit becomes a

circuit breaker. The TPS24710/11/12/13 will turn off the MOSFET, M1, after a fault timer period once the load

exceeds the current limit threshold.

ACTION OF THE CONSTANT-POWER ENGINE

Figure 27 illustrates the operation of the constant-power engine during start-up. The circuit used to generate the

waveforms of Figure 27 was programmed to a power limit of 29.3 W by means of the resistor connected between

PROG and GND. At the moment current begins to flow through the MOSFET, a voltage of 12 V appears across

it (input voltage V

VCC

= 12 V), and the constant-power engine therefore allows a current of 2.44 A (equal to 29.3

W divided by 12 V) to flow. This current increases in inverse ratio as the drain-to-source voltage diminishes, so

as to maintain a constant dissipation of 29.3 W. The constant-power engine adjusts the current by altering the

reference signal fed to the current limit amplifier. The lower part of Figure 28 shows the measured power

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