TPS2346PWRG4【PDF 11/30 页】IC HOT SWAP POWER MGR 24-TSSOP

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Sheet目录47

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TPS2346

SLUS529 MAY 2002

www.ti.com

detailed description (continued)

The basic functional blocks of the LCA/voltage sense circuits is shown in greater detail in Figure 2. The LCA

has as its inputs the reference voltage generated by the current sources, and the current sense input. During

a supply turn-on, it slews the pass MOSFET gate to force the load current to track the selected source. After

load charging completes, and the current decays to the nominal operating level, the LCA drives the GATEx

output to its input supply level, the charge pump output voltage.

UDG02004

LCA

OCA

DAC

REF_Vx

VSEL

VINx

CSx

VSx

GATEx

OCx

UVOVx

MUX

2:1

CPUMP

IMAX

IRAMP

INX

Figure 2. Linear Control Amplifier Block

The supply voltage is monitored by the undervoltage (UV) and overvoltage (OV) comparators. A voltage

multiplexer (MUX) selects from either the input supply voltage (VINx) or the load voltage (VSx), and provides

that signal to the comparator inputs. Once the Channel 1 supply is above the UVLO threshold, and the ENABLE

input has been pulled low, but prior to the ramp-up of the first channel, the comparators monitor the input

supplies. Any supply outside its UV/OV window causes all pass MOSFETs to be held off. If all inputs are within

tolerance, a ramp-up sequence can start, at which time the comparator inputs are switched over to the load,

or VSx, voltages. Within the state machine, monitoring of the ORed status of the UV and OV comparators of

any channel is enabled at the turn-on of the next channel, or approximately at the leading edge of the next

IRAMP pulse.

Finally, a fast overcurrent comparator (OCA in the diagram) also monitors the CSx input. This comparator

threshold is set to approximately 2 times the current limit threshold, (2 ?IMAX) for the three positive supplies.

In the event of a short-circuit or other fast overcurrent event, the OCA trips, disabling the LCA, and causing

additional gate discharge paths to be turned on for a rapid shutdown of the loads.

A 1-礢 to 2-礢 filter is applied to all overcurrent and voltage faults to guard against nuisance trips. If the duration

of a fault condition on any one channel exceeds the filter length, the fault is latched, the open-drain device at

the PG

output is turned off, and all four channels are shut down.

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