Datasheet

PD
L
LIMFtyppeak
t
L
V
II ×+=
)(
( )
L)on(DSOUT(min)OUT(min)IN
RRIVV ++=
TPS62160
TPS62161, TPS62162, TPS62163
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SLVSAM2C NOVEMBER 2011REVISED SEPTEMBER 2013
100% Duty-Cycle Operation
The duty cycle of the buck converter is given by D=Vout/Vin and increases as the input voltage comes close to
the output voltage. In this case, the device starts 100% duty cycle operation turning on the high-side switch
100% of the time. The high-side switch stays turned on as long as the output voltage is below the internal
setpoint. This allows the conversion of small input to output voltage differences, e.g. for longest operation time of
battery-powered applications. In 100% duty cycle mode, the low-side FET is switched off.
The minimum input voltage to maintain output voltage regulation, depending on the load current and the output
voltage level, can be calculated as:
(3)
where
I
OUT
is the output current,
R
DS(on)
is the R
DS(on)
of the high-side FET and
R
L
is the DC resistance of the inductor used.
Enable / Shutdown (EN)
When Enable (EN) is set High, the device starts operation.
Shutdown is forced if EN is pulled Low with a shutdown current of typically 1.5µA. During shutdown, the internal
power MOSFETs as well as the entire control circuitry are turned off. The internal resistive divider pulls down the
output voltage smoothly. If the EN pin is Low, an internal pull-down resistor of about 400kΩ is connected and
keeps it Low, to avoid bouncing. To avoid ON/OFF oscillations, a minimum slew rate of about 50mV/s is
recommended for the EN signal.
Connecting the EN pin to an appropriate output signal of another power rail provides sequencing of multiple
power rails.
Softstart
The internal soft start circuitry controls the output voltage slope during startup. This avoids excessive inrush
current and ensures a controlled output voltage rise time. It also prevents unwanted voltage drops from high-
impedance power sources or batteries. When EN is set to start device operation, the device starts switching after
a delay of about 50µs and V
OUT
rises with a slope of about 25mV/µs. See Figure 29 and Figure 30 for typical
startup operation.
The TPS6216X can start into a pre-biased output. During monotonic pre-biased startup, the low-side MOSFET is
not allowed to turn on until the device's internal ramp sets an output voltage above the pre-bias voltage.
Current Limit And Short Circuit Protection
The TPS6216X devices are protected against heavy load and short circuit events. At heavy loads, the current
limit determines the maximum output current. If the current limit is reached, the high-side FET will be turned off.
Avoiding shoot through current, the low-side FET will be switched on to sink the inductor current. The high-side
FET will turn on again, only if the current in the low-side FET has decreased below the low side current limit
threshold.
The output current of the device is limited by the current limit (see ELECTRICAL CHARACTERISTICS). Due to
internal propagation delay, the actual current can exceed the static current limit during that time. The dynamic
current limit can be calculated as follows:
(4)
where
I
LIMF
is the static current limit, specified in the electrical characteristic table,
L is the inductor value,
V
L
is the voltage across the inductor and
t
PD
is the internal propagation delay.
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