TPS62050DGSR Datasheet, PDF (11/25 Pages) Texas Instruments – 800-mA SYNCHRONOUS STEP-DOWN CONVERTER

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TPS62052, TPS62054
TPS62056, TPS62050, TPS62051
SLVS432E – SEPTEMBER 2002 – REVISED JUNE 2011
1.6%
0.8%
VO, nominal
–1.6%
t
Figure 17. Power-Save Mode Output Voltage Thresholds
The converter enters the fixed frequency PWM mode again as soon as the output voltage falls below the comp
low 2 threshold set to 1.6% below V_O, nominal.
Soft-Start
The TPS6205x has an internal soft-start circuit that limits the inrush current during start-up. This prevents
possible voltage drops of the input voltage if a battery or a high impedance power source is connected to the
input of the TPS6205x.
The soft-start is implemented as a digital circuit increasing the switch current in steps of 200 mA, 400 mA, 800
mA and then the typical switch current limit of 1.2 A. Therefore the start-up time mainly depends on the output
capacitor and load current. Typical start-up time with a 22-µF output capacitor and a 200-mA load current is 1
ms.
100% Duty Cycle Low Dropout Operation
The TPS6205x offers the lowest possible input to output voltage difference while still maintaining operation with
the use of the 100% duty cycle mode. In this mode, the P-channel switch is constantly turned on. This is
particularly useful in battery powered applications to achieve longest operation time by taking full advantage of
the whole battery voltage range, i.e. The minimum input voltage to maintain regulation depends on the load
current and output voltage and can be calculated as:
ǒ Ǔ V_I(min) + V_O(max) ) I_O(max) r_DS(on)(max) ) R_L
I_O(max) = Maximum output current plus inductor ripple current
r_DS(on)(max) = Maximum P-Channel switch r_DS(on)
R_L = DC resistance of the inductor
V_O(max) = Nominal output voltage plus maximum output voltage tolerance
Enable and Overtemperature Protection
Logic low on EN forces the TPS6205x into shutdown. In shutdown, the power switch, drivers, voltage reference,
oscillator, and all other functions are turned off. The supply current is reduced to less than 2 µA in the shutdown
mode. When the device is in thermal shutdown, the bandgap is forced to stay on even if the device is set into
shutdown by pulling EN to GND. As soon as the temperature drops below the threshold, the device automatically
starts again.
If an output voltage is present when the device is disabled, which could be an external voltage source or super
cap, the reverse leakage current is specified under electrical characteristics. Pulling the enable pin high starts up
the TPS6205x with the soft-start as described under the paragraph soft-start. If the EN pin is connected to any
voltage other than V_I or GND, an increased leakage current of typically 10 µA and up to 20 µA can occur.
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