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TPS63021DSJT Datasheet(HTML) 14 Page - Texas Instruments
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SLVS916 – APRIL 2010
Dynamic Current Limit
To protect the device and the application, the average inductor current is limited internally on the IC. At nominal
operating conditions, this current limit is constant. The current limit value can be found in the electrical
characteristics table. If the supply voltage at VIN drops below 2.3V, the current limit is reduced. This can happen
when the input power source becomes weak. Increasing output impedance, when the batteries are almost
discharged, or an additional heavy pulse load is connected to the battery can cause the VIN voltage to drop. The
dynamic current limit has its lowest value when reaching the minimum recommended supply voltage at VIN. At
this voltage, the device is forced into burst mode operation trying to stay active as long as possible even with a
weak input power source.
If the die temperature increases above the recommended maximum temperature, the dynamic current limit
becomes active. Similar to the behavior when the input voltage at VIN drops, the current limit is reduced with
Smart Power Good
The device has a built in power good function to indicate whether the output voltage is regulated properly. As
soon as the average inductor current is limited to a value below the current the voltage regulator demands for
maintaining the output voltage the power good output goes low impedance. The output is open drain, so its logic
function can be adjusted to any voltage level the connected logic is using, by connecting a pull up resistor to the
supply voltage of the logic. By monitoring the status of the current control loop, the power good output provides
the earliest indication possible for an output voltage break down and leaves the connected application a
maximum time to safely react.
The device is put into operation when EN is set high. It is put into a shutdown mode when EN is set to GND. In
shutdown mode, the regulator stops switching, all internal control circuitry is switched off and the load is
disconnected from the input. This means that the output voltage can drop below the input voltage during
shutdown. During start-up of the converter, the duty cycle and the peak current are limited in order to avoid high
peak currents flowing from the input.
Softstart and Short Circuit Protection
After being enabled, the device starts operating. The average current limit ramps up from an initial value of about
500mA following the increasing output voltage. At an output voltage of about 1.2V, the current limit is at its
nominal value. If the output voltage does not increase, the current limit will not increase. There is no timer
implemented. Thus, the output voltage overshoot at startup, as well as the inrush current, is kept at a minimum.
The device ramps up the output voltage in a controlled manner even if a large capacitor is connected at the
output. If the output voltage does not increase above 1.2V, the device assumes a short circuit at the output and
keeps the current limit low to protect itself and the application. At a short on the output during operation, the
internal clock frequency and the current limit are also decreased accordingly. At 0 V on the output, the output
current will be limited in the range of 400 mA.
An undervoltage lockout function prevents device start-up if the supply voltage on VINA is lower than
approximately its threshold (see electrical characteristics table). When in operation, the device automatically
enters the shutdown mode if the voltage on VINA drops below the undervoltage lockout threshold. The device
automatically restarts if the input voltage recovers to the minimum operating input voltage.
The device has a built-in temperature sensor which monitors the internal IC temperature. If the temperature
exceeds the programmed threshold (see electrical characteristics table) the device stops switching. As soon as
the IC temperature has decreased below the programmed threshold, it starts switching again. There is a built-in
hysteresis to avoid unstable operation at IC temperatures at the overtemperature threshold.
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Product Folder Link(s): TPS63020 TPS63021
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