TPS61021A Datasheet, PDF (10/33 Pages) Texas Instruments – TPS61021A 3-A Boost Converter with 0.5-V Ultra Low Input Voltage

TPS61021A
SLVSDM0 – JUNE 2016
www.ti.com
Feature Description (continued)
7.3.5 Pass-Through Operation
When the input voltage is higher than the setting output voltage, the output voltage is higher than the target
regulation voltage. When the output voltage is 101% of the setting target voltage, the TPS61021A stops
switching and turns on the high side PMOS FET. The device works in pass-through mode. The output voltage is
the input voltage minus the voltage drop across the dc resistance (DCR) of the inductor and the on-resistance
(R_DS(on)) of the PMOS FET. When the output voltage drops below the 98% of the setting target voltage as the
input voltage declines or the load current increases, the TPS61021A resumes switching again to regulate the
output voltage.
7.3.6 Over-Voltage Protection
The TPS61021A has an output over-voltage protection (OVP) to protect the device in case that the external
feedback resistor divider is wrongly populated. When the output voltage is above 4.35 V typically, the device
stops switching. Once the output voltage falls 0.1 V below the OVP threshold, the device resumes operating
again. To prevent the high overshoot voltage during OVP when the FB pin voltage is too much lower than the
internal reference voltage, the TPS61021A limits the valley swtich current to approximate 100 mA when the FB
pin voltage is below 0.2 V and the output voltage is above 2.9V.
7.3.7 Output Short-to-Ground Protection
The TPS61021A starts to limit the output current when the output voltage is below 1.6 V. The lower the output
voltage reaches, the smaller the output current is. When the output voltage is below 1 V, the output current is
limited to approximate 100 mA. Once the short circuit is released, the TPS61021A goes through the soft startup
again to output the regulated voltage.
7.3.8 Thermal Shutdown
The TPS61021A goes into thermal shutdown once the junction temperature exceeds 150°C. When the junction
temperature drops below the thermal shutdown temperature threshold less the hysteresis, typically 130°C, the
device starts operating again.
7.4 Device Functional Modes
The TPS61021A has two switching operation modes, PWM mode in moderate to heavy load conditions and
power save mode with pulse frequency modulation (PFM) in light load conditions.
7.4.1 PWM Mode
The TPS61021A uses a quasi-constant 2.0-MHz frequency pulse width modulation (PWM) at moderate to heavy
load current. Based on the input voltage to output voltage ratio, a circuit predicts the required on-time. At the
beginning of the switching cycle, the NMOS switching FET, shown in the functional block diagram, is turned on.
The input voltage is applied across the inductor and the inductor current ramps up. In this phase, the output
capacitor is discharged by the load current. When the on-time expires, the main switch NMOS FET is turned off,
and the rectifier PMOS FET is turned on. The inductor transfers its stored energy to replenish the output
capacitor and supply the load. The inductor current declines because the output voltage is higher than the input
voltage. When the inductor current hits a value which the error amplifier outputs, the next switching cycle starts
again.
The TPS61021A has a built-in compensation circuit that can accommodate a wide range of input voltage, output
voltage, inductor value and output capacitor value for stable operation.
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