TL1963A-XX Datasheet, PDF (17/26 Pages) Texas Instruments – 1.5-A LOW-NOISE FAST-TRANSIENT-RESPONSE LOW-DROPOUT REGULATOR

TL1963A-xx
www.ti.com ........................................................................................................................................................ SLVS719A – JUNE 2008 – REVISED AUGUST 2008
The problem occurs with a heavy output load when the input voltage is high and the output voltage is low.
Common situations are immediately after the removal of a short circuit or when the shutdown pin is pulled high
after the input voltage has already been turned on. The load line for such a load may intersect the output current
curve at two points. If this happens, there are two stable output operating points for the regulator. With this
double intersection, the input power supply may need to be cycled down to zero and brought up again to make
the output recover.
Output Voltage Noise
The TL1963A-xx regulators have been designed to provide low output voltage noise over the 10-Hz to 100-kHz
bandwidth while operating at full load. Output voltage noise is typically 40 nV/√Hz over this frequency bandwidth
for the TL1963A (adjustable version). For higher output voltages (generated by using a resistor divider), the
output voltage noise is gained up accordingly. This results in RMS noise over the 10-Hz to 100-kHz bandwidth of
14 µV_RMS for the TL1963A, increasing to 38 µV_RMS for the TL1963A-3.3.
Higher values of output voltage noise may be measured when care is not exercised with regards to circuit layout
and testing. Crosstalk from nearby traces can induce unwanted noise onto the output of the TL1963A-xx.
Power-supply ripple rejection must also be considered; the TL1963A-xx regulators do not have unlimited
power-supply rejection and pass a small portion of the input noise through to the output.
Thermal Considerations
The power handling capability of the device is limited by the maximum rated junction temperature (125°C). The
power dissipated by the device is made up of two components:
1. Output current multiplied by the input/output voltage differential: I_OUT(V_IN – V_OUT)
2. GND pin current multiplied by the input voltage: I_GNDV_IN.
The GND pin current can be found using the GND Pin Current graphs in Typical Characteristics. Power
dissipation is equal to the sum of the two components listed above.
The TL1963A-xx series regulators have internal thermal limiting designed to protect the device during overload
conditions. For continuous normal conditions, the maximum junction temperature rating of 125°C must not be
exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to
ambient. Additional heat sources mounted nearby must also be considered.
For surface-mount devices, heat sinking is accomplished by using the heat-spreading capabilities of the PC
board and its copper traces. Copper board stiffeners and plated through-holes also can be used to spread the
heat generated by power devices.
Table 1 lists thermal resistance for several different board sizes and copper areas. All measurements were taken
in still air on 1/16-inch FR-4 board with one-ounce copper.
Table 1. KTT Package (5-Pin TO-263)
COPPER AREA
TOPSIDE ⁽¹⁾
BACKSIDE
2500 mm²
2500 mm²
1000 mm²
2500 mm²
125 mm²
2500 mm²
BOARD AREA
2500 mm²
2500 mm²
2500 mm²
THERMAL RESISTANCE
(JUNCTION TO AMBIENT)
23°C/W
25°C/W
33°C/W
(1) Device is mounted on topside.
Copyright © 2008, Texas Instruments Incorporated
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