Datasheet

-470.02
R
(RSET)
V - 0.00314
(OFF)
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TPS2419
SLVS998B –FEBRUARY 2010–REVISED SEPTEMBER 2011 www.ti.com
DETAILED DESCRIPTION
The following descriptions refer to the pinout and the functional block diagram.
A, C: The A pin serves as the simulated diode anode and the C as the cathode. GATE is driven high when V
(A-C)
exceeds 65 mV. A strong GATE pull-down is applied when V
(A-C)
is less than the programmable turn-off threshold
(see RSET). These two thresholds serve as a hysteretic GATE control with the ON/OFF state preserved until the
next (opposite) threshold cross.
The internal charge pump output, which provides bias power to the comparators and voltage to drive GATE, is
referenced to A. Some charge pump current appears on A.
C is both the cathode voltage sense and the bias supply for the gate-drive charge pump and other internal
circuits. This pin must be connected a source that is 3 V or greater when the external MOSFET is to be turned
on.
A 0.01-μF minimum bypass capacitor to GND is recommended for both A and C inputs. A and C connections to
the bypass capacitor and the controlled MOSFET should be short and low impedance.
The inputs are protected from excess differential voltage by a clamp diode and series resistance. If C falls below
A by more than about 0.7 V, a small current flows out of C. Configurations which permit C to be more than 6 V
lower than A should be avoided.
BYP: BYP is the internal charge pump output, and the positive supply voltage for internal comparator circuits and
GATE driver. A capacitor must be connected from BYP to A. While the capacitor value is not critical, a 2200-pF
ceramic is recommended. Traces to this part must be kept short and low impedance to provide adequate filtering.
Shorting this pin to a voltage below A damages the TPS2419.
EN: A voltage greater than 1.3 V on EN permits the TPS2419 to operate in its normal ORing mode. A voltage
below the lower threshold forces GATE to remain low, however EN going high will not automatically turn GATE
ON. EN going low when GATE is high engages the sustain current pulldown. EN should not be driven higher
than its recommended maximum voltage.
GATE: Gate controls the external N channel MOSFET gate. GATE is driven positive with respect to A by a driver
operating from the voltage on BYP. A time-limited high current discharge source pulls GATE to GND when the
turn-off comparator is activated. The high-current discharge is followed by a sustaining pull-down. The turn-off
circuits are disabled by the thermal shutdown, leaving a resistive pull-down to keep the gate from floating. The
gate connection should be kept low impedance to maximize turn-off current.
GND: This is the input supply reference. GND should have a low impedance connection to the ground plane. It
carries several Amperes of rapid-rising discharge current when the external MOSFET is turned off, and also
carries significant charge pump currents.
RSET: A resistor connected from this pin to GND sets the V
(A-C)
turn-off comparator threshold. The threshold is
slightly positive when the RSET pin is left open. Current drawn by the resistor programs the turn-off voltage to
increasing negative values. The TPS2419 must have a negative threshold programmed to avoid an unstable
condition at light load. The expression for R
(RSET)
in terms of the turn-off voltage ( V
(OFF)
= V
(A)
- V
(C)
) follows.
(1)
The units of the numerator are (V × V/A). V
(OFF)
is positive for V
(A)
greater than V
(C)
, V
(OFF)
is less than 3 mV, and
R
(RSET)
is in ohms.
RSVD: Connect to ground.
6 Copyright © 2010–2011, Texas Instruments Incorporated
Product Folder Link(s): TPS2419