Datasheet

TPS2394

SLVSAA9 –AUGUST 2010

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OV: Over voltage comparator input. This input is typically connected to a voltage divider between RTN and

SOURCE to sense the magnitude of the input supply. If OV is less than 1.4 V above SOURCE, and UV is more

than 1.4 V above SOURCE, and there is no fault, the linear current amp will be enabled. In the event of a fault,

pulling OV high or UV low will reset the fault latch and allow the IC to restart. OV can also be used as an

active-low logic enable input. The over-voltage comparator hysteresis is programmed by the equivalent

resistance seen looking into the divider at the OV input.

RAMP: Programming input for setting inrush current and current slew rate. An external capacitor connected

between RAMP and SOURCE establishes turn-on current slew rate. During turn-on, TPS2394 charges this

capacitor to establish the reference input to the LCA at 1% of the voltage from RAMP to SOURCE. The

closed-loop control of the LCA and the pass MOSFET maintains the V(SENSE - SOURCE) at the reference

potential, so the load current slew rate is directly set by the voltage ramp rate at the RAMP pin. When fully

charged, RAMP can exceed SOURCE by 6 V, but the reference is internally clamped to 42 mV, limiting load

current to 42 mV/R

SENSE

. When the output is disabled via OV, UV, or due to a load fault, the RAMP capacitor is

discharged and held low to initialize for the next turn on.

The TPS2394 initiates ramp capacitor charging, and consequently load current slewing, at a reduced rate. This

reduced rate applies until the voltage on the RAMP pin is about 0.5 V. The maximum di/dt rate, as set by

Equation 2, is effective once the device switches to a 10-mA charging source.

RTN: Positive supply input. For negative voltage systems, this pin connects directly to the return node of the

input power bus.

SENSE: Current sense input. An external low-value resistor connected between SENSE and SOURCE is used

to monitor current magnitude. There are two internal device thresholds associated with the voltage at the SENSE

pin. During ramp-up of the load capacitance or during other periods of excessive demand, the linear current amp

(LCA) will regulate this voltage to 42 mV. Whenever the LCA is in current regulation mode, the FLTTIM capacitor

charges. If the LCA output is at its maximum, GAT is pulled 14 V above SOURCE. At this time, a fast fault such

as a short circuit can cause the SENSE voltage to rapidly exceed 120 mV (the overload threshold). In this case,

the GAT pin is pulled low rapidly, bypassing the fault timer.

SOURCE: Connection to the input supply negative rail.

UV: Under Voltage Comparator input. This input is typically connected to a voltage divider between RTN and

SOURCE to sense the magnitude of the input supply. If UV is more than 1.4 V above SOURCE, OV is less than

1.4 V above SOURCE, and there is no fault, the LCA will be enabled. In the event of a fault, pulling UV low or

OV high will reset the fault latch and allow restarting. UV can also be used as an active high logic enable input.

The under-voltage comparator hysteresis is programmed by the equivalent resistance seen looking into the

divider at the UV input.

Product Folder Link(s): TPS2394