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TPS61099, TPS610994, TPS610997

SLVSD88C – JULY 2016 – REVISED JANUARY 2017

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Product Folder Links: TPS61099 TPS610994 TPS610997

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Feature Description (continued)

8.3.4 Soft Start

After the EN pin is tied to high voltage, the TPS61099x begins to startup. At the beginning, the device operates

at the boundary of Discontinuous Conduction Mode (DCM) and Continuous Conduction Mode (CCM), and the

inductor peak current is limited to around 200 mA during this stage. When the output voltage is charged above

approximately 1.6 V, the device starts the hysteretic current mode operation. The current limit threshold is

by the output of an internal error amplifier which compares the feedback of the output voltage and the internal

reference voltage.

The TPS61099x is able to start up with 0.7-V input voltage with larger than 3-k

Ω load. However, if the load during

startup is so heavy that the TPS61099x fails to charge the output voltage above 1.6 V, the TPS61099x can't start

up successfully until the input voltage is increased or the load current is reduced. The startup time depends on

input voltage and load current.

8.3.5 Current Limit Operation

The TPS61099x employs cycle-by-cycle over-current protection (OCP) function. If the inductor peak current

current. In this case the output voltage will decrease until the power balance between input and output is

achieved. If the output drops below the input voltage, the TPS61099x enters into Down Mode. The peak current

startup process again. In Pass-Through operation, current limit function is not enabled.

8.3.6 Output Short-to-Ground Protection

The TPS61099x starts to limit the switch current to 200 mA when the output voltage is below 1.6 V. If short-to-

ground condition occurs, switch current is limited at 200 mA. Once the short circuit is released, the TPS61099x

goes back to soft start again and regulates the output voltage.

8.3.7 Over Voltage Protection

TPS61099x 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 of the TPS61099 exceeds the OVP threshold of

5.8 V, the device stops switching. Once the output voltage falls 0.1 V below the OVP threshold, the device starts

operating again.

8.3.8 Down Mode Regulation and Pass-Through Operation

The TPS61099x features Down Mode and Pass-Through operation when input voltage is close to or higher than

output voltage.

the behavior of the rectifying PMOS by pulling its gate to input voltage instead of to ground. In this way, the

voltage drop across the PMOS is increasing as high as to regulate the output voltage. The power loss also

increases in this mode, which needs to be taken into account for thermal consideration.

In the Pass-Through operation, the boost converter stops switching. The rectifying PMOS constantly turns on

and low side switch constantly turns off. The output voltage is the input voltage minus the voltage drop across

the dc resistance (DCR) of the inductor and the on-resistance of the rectifying PMOS.

output voltage follows input voltage. The TPS61099x exits Pass-Through Mode and goes back to Down Mode

below the output voltage, returning to Boost operation.