Datasheet

0
VIN-VOUT-mV
0 20 60 100 140
IDS-StaticDrain-SourceCurrent- A
3.0
0.5
1.0
1.5
2.0
2.5
T =125°C
J
T =-40°C
J
T =25°C
J
160
R =24.9k
ILIM
Ω
40 80 120
5.0
4.5
4.0
3.5
TPS2556
TPS2557
www.ti.com SLVS931A – NOVEMBER 2009– REVISED FEBRUARY 2012
TYPICAL CHARACTERISTICS (continued)
Figure 18. Switch Current vs. Drain-Source Voltage Across Switch
DETAILED DESCRIPTION
OVERVIEW
The TPS2556/57 is a current-limited, power-distribution switch using N-channel MOSFETs for applications where
short circuits or heavy capacitive loads will be encountered. This device allows the user to program the
current-limit threshold between 500 mA and 5.0 A (typ) via an external resistor. This device incorporates an
internal charge pump and the gate drive circuitry necessary to drive the N-channel MOSFET. The charge pump
supplies power to the driver circuit and provides the necessary voltage to pull the gate of the MOSFET above the
source. The charge pump operates from input voltages as low as 2.5 V and requires little supply current. The
driver controls the gate voltage of the power switch. The driver incorporates circuitry that controls the rise and fall
times of the output voltage to limit large current and voltage surges and provides built-in soft-start functionality.
The TPS2556/57 family limits the output current to the programmed current-limit threshold I
OS
during an
overcurrent or short-circuit event by reducing the charge pump voltage driving the N-channel MOSFET and
operating it in the linear range of operation. The result of limiting the output current to I
OS
reduces the output
voltage at OUT because N-channel MOSFET is no longer fully enhanced.
OVERCURRENT CONDITIONS
The TPS2556/57 responds to overcurrent conditions by limiting their output current to I
OS
. When an overcurrent
condition is detected, the device maintains a constant output current and the output voltage reduces accordingly.
Two possible overload conditions can occur.
The first condition is when a short circuit or partial short circuit is present when the device is powered-up or
enabled. The output voltage is held near zero potential with respect to ground and the TPS2556/57 ramps the
output current to I
OS
. The TPS2556/57 will limit the current to I
OS
until the overload condition is removed or the
device begins to thermal cycle.
The second condition is when a short circuit, partial short circuit, or transient overload occurs while the device is
enabled and powered on. The device responds to the overcurrent condition within time t
IOS
(see Figure 3). The
current-sense amplifier is overdriven during this time and momentarily disables the internal N-channel MOSFET.
The current-sense amplifier recovers and ramps the output current to I
OS
. Similar to the previous case, the
TPS2556/57 will limit the current to I
OS
until the overload condition is removed or the device begins to thermal
cycle.
The TPS2556/57 thermal cycles if an overload condition is present long enough to activate thermal limiting in any
of the above cases. The device turns off when the junction temperature exceeds 135°C (min) while in current
limit. The device remains off until the junction temperature cools 20°C (typ) and then restarts. The TPS2556/57
cycles on/off until the overload is removed (see Figure 10) .
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Product Folder Link(s): TPS2556 TPS2557