TL1963A-XX Datasheet, PDF (18/26 Pages) Texas Instruments – 1.5-A LOW-NOISE FAST-TRANSIENT-RESPONSE LOW-DROPOUT REGULATOR

TL1963A-xx
SLVS719A – JUNE 2008 – REVISED AUGUST 2008 ........................................................................................................................................................ www.ti.com
Calculating Junction Temperature
Example: Given an output voltage of 3.3 V, an input voltage range of 4 V to 6 V, an output current range of 0 mA
to 500 mA, and a maximum ambient temperature of 50°C, what is the maximum junction temperature?
The power dissipated by the device is equal to:
I_OUT(MAX)(V_IN(MAX) – V_OUT) + I_GND(V_IN(MAX))
where,
I_OUT(MAX) = 500 mA
V_IN(MAX) = 6 V
I_GND at (I_OUT = 500 mA, V_IN = 6 V) = 10 mA
So,
P = 500 mA (6 V – 3.3 V) + 10 mA (6 V) = 1.41 W
Using a KTT package, the thermal resistance is in the range of 23°C/W to 33°C/W, depending on the copper
area. So the junction temperature rise above ambient is approximately equal to:
1.41 W × 28°C/W = 39.5°C
The maximum junction temperature is then be equal to the maximum junction-temperature rise above ambient
plus the maximum ambient temperature or:
T_JMAX = 50°C + 39.5°C = 89.5°C
Protection Features
The TL1963A-xx regulators incorporate several protection features that make them ideal for use in
battery-powered circuits. In addition to the normal protection features associated with monolithic regulators, such
as current limiting and thermal limiting, the devices are protected against reverse input voltages, reverse output
voltages and reverse voltages from output to input.
Current limit protection and thermal overload protection are intended to protect the device against current
overload conditions at the output of the device. For normal operation, the junction temperature should not exceed
125°C.
The input of the device withstands reverse voltages of 20 V. Current flow into the device is limited to less than
1 mA (typically less than 100 µA), and no negative voltage appears at the output. The device protects both itself
and the load. This provides protection against batteries that can be plugged in backward.
The output of the TL1963A-xx can be pulled below ground without damaging the device. If the input is left open
circuit or grounded, the output can be pulled below ground by 20 V. For fixed voltage versions, the output acts
like a large resistor, typically 5 kΩ or higher, limiting current flow to typically less than 600 µA. For adjustable
versions, the output acts like an open circuit; no current flows out of the pin. If the input is powered by a voltage
source, the output sources the short-circuit current of the device and protects itself by thermal limiting. In this
case, grounding the SHDN pin turns off the device and stops the output from sourcing the short-circuit current.
The ADJ pin of the adjustable device can be pulled above or below ground by as much as 7 V without damaging
the device. If the input is left open circuit or grounded, the ADJ pin acts like an open circuit when pulled below
ground and like a large resistor (typically 5 kΩ) in series with a diode when pulled above ground.
In situations where the ADJ pin is connected to a resistor divider that would pull the ADJ pin above its 7-V clamp
voltage if the output is pulled high, the ADJ pin input current must be limited to less than 5 mA. For example, a
resistor divider is used to provide a regulated 1.5-V output from the 1.21-V reference when the output is forced to
20 V. The top resistor of the resistor divider must be chosen to limit the current into the ADJ pin to less than
5 mA when the ADJ pin is at 7 V. The 13-V difference between OUT and ADJ pins divided by the 5-mA
maximum current into the ADJ pin yields a minimum top resistor value of 2.6 kΩ.
In circuits where a backup battery is required, several different input/output conditions can occur. The output
voltage may be held up while the input is either pulled to ground, pulled to some intermediate voltage, or is left
open circuit.
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