this inductor current depending on the output load. If the required average input current is lower than average

inductor current defined by this constant ripple current, the inductor current becomes discontinuous to keep the

efficiency high under light load conditions. Figure 7-1 illustrates the hysteretic current operation.

The output voltage VOUT is monitored via the internal feedback network connected to a voltage error amplifier.

To regulate the output voltage, the voltage error amplifier compares this feedback voltage to the internal voltage

reference and adjusts the required offset of the inductor current accordingly.

IL

t

200mA

Continuous Current Operation

Discontinuous Current Operation

200mA

Figure 7-1. Hysteretic Current Operation

7.3.3

The TPS61322xx boost converter can increase the output load capacity by connecting an external schottky

diode from SW pin to VOUT pin. Higher than 500 mA output current is supported for 5-V output voltage

applications such as USB OTG and HDMI power supply. For such applications, an adaptive constant off time

circuit will generate the signal to turn off high-side FET. The inductor current ripple is greater than 200 mA if with

this external diode. A higher inductance can help reduce the inductor current ripple.

7.3.4 Undervoltage Lockout

An undervoltage lockout function stops operation of the converter if the input voltage drops below the typical

undervoltage lockout threshold of 0.4 V while the output voltage is still higher than 1.8 V. A hysteresis of 100 mV

is added so that the device does not switch again until the input voltage goes up to 0.5 V.

7.3.5 Current Limit Operation

The TPS61322xx employs cycle-by-cycle peak current limit operation. If the inductor peak current hits the peak

current limit ILIM, the low-side MOSFET is turned off and stops the further increase of the inductor current. In

this case the output voltage drops until power balance between the input side and output side is achieved. If the

output voltage drops below the input voltage, the inductor current will be clamped by the DCR of the inductor and

the on-resistance (Rds,on) of the high-side MOSFET.

7.3.6 Overtemperature Protection

The TPS61322xx has a built-in temperature sensor which monitors the internal junction temperature in boost

mode operation. If the junction temperature exceeds the threshold 150°C, the device stops operating. As soon

as the junction temperature drops below the shutdown temperature minus the hysteresis, typically 130°C, the

device starts operating again.

7.3.7 Device Functional Modes

• Section 7.3.2 - Continuous and discontinuous current operation

• Protective mechanisms

– Section 7.3.5

– Section 7.3.4

– Section 7.3.6

TPS61322

SLVSDY5E – JANUARY 2018 – REVISED FEBRUARY 2024

www.ti.com

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