DFE252012PD-2R2M datasheet(39/54 Pages) TI

39 / 54 page

When implementing an IBB design, it is important to understand that the IC ground is tied to the negative voltage

rail, and in turn, the electrical characteristics of the TPS629211-Q1 device are referenced to this rail. During

power up, as there is no charge in the output capacitor, the IC GND pin (and VOUT) are effectively 0 V, thus

parameters such as the VIN UVLO and EN thresholds are the same as in a typical buck configuration. However,

after the output voltage is in regulation, due to the negative voltage on the IC GND pin, the device traditionally

continues to operate below what can appear to be the normal UVLO/EN falling thresholds relative to the system

ground. Thus, special care must be taken if the user is using the dynamic mode change feature on the MODE

pin of the TPS629211-Q1 or driving the EN pin from an upstream microcontroller as the high and low thresholds

are relative to the negative rail and not the system ground.

More information on using a DCS regulator in an IBB configuration can be found in the Description

Compensating the Current Mode Boost Control Loop Application Note and Using the TPS6215x in an Inverting

Buck-Boost Topology Application Note.

VIN

MODE/

S-CONF

VOS

FB/

VSET

10 F

22 F

2.2 µH

VOUT

-0.6 V to -5.5 V

GND

TPS6292xx

Figure 9-77. IBB Example with Adjustable Feedback

VIN

MODE/

S-CONF

VOS

FB/

VSET

10 F

22 F

2.2 µH

VOUT

-0.4 V to -5.5 V

GND

TPS6292xx

Figure 9-78. IBB Example with Internal Feedback

9.4 Power Supply Recommendations

The power supply to the TPS629211-Q1 must have a current rating according to the supply voltage, output

voltage, and output current of the TPS629211-Q1.

9.5 Layout

9.5.1 Layout Guidelines

A proper layout is critical for the operation of a switched mode power supply, even more so at high switching

frequencies. Therefore, the PCB layout of the TPS629211-Q1 demands careful attention to make sure proper

operation and to get the performance specified. A poor layout can lead to issues like the following:

• Poor regulation (both line and load)

• Stability and accuracy weaknesses

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TPS629211-Q1

SLVSGD0A – MARCH 2022 – REVISED MARCH 2023

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