7.2.2.3 Input Capacitor Selection

Multilayer X5R or X7R ceramic capacitors are excellent choices for the input decoupling of the step-up converter

as they have extremely low ESR and are available in small footprints. Input capacitors must be located as close

as possible to the device. While a 22μF input capacitor is sufficient for most applications, larger values may

be used to reduce input current ripple without limitations. Take care when using only ceramic input capacitors.

When a ceramic capacitor is used at the input and the power is being supplied through long wires, a load step

at the output can induce ringing at the input voltage. This ringing can couple to the output and be mistaken as

loop instability or even damage the part. In this circumstance, place additional bulk capacitance (tantalum or

aluminum electrolytic capacitor) between ceramic input capacitor and the power source to reduce ringing that

can occur between the inductance of the power source leads and ceramic input capacitor.

7.3 Power Supply Recommendations

The device is designed to operate from an input voltage supply range between 1.8V to 5.5V. This input supply

must be well regulated. If the input supply is located more than a few inches from the converter, additional bulk

capacitance may be required in addition to the ceramic bypass capacitors. A typical choice is a tantalum or

aluminum electrolytic capacitor with a value of 100µF. Output current of the input power supply must be rated

according to the supply voltage, output voltage, and output current of the TPSM81033.

7.4 Layout

7.4.1 Layout Guidelines

As for all switching power supplies, especially those running at high switching frequency and high currents,

layout is an important design step. If the layout is not carefully done, the regulator suffers from instability and

noise problems. To maximize efficiency, switch rise and fall time are very fast. To prevent radiation of high

frequency noise (for example, EMI), proper layout of the high-frequency switching path is essential. The input

capacitor needs not only to be close to the VIN pin, but also to the GND pin in order to reduce input supply

ripple.

The most critical current path for all boost converters is from the switching FET, through the rectifier FET, then

the output capacitors, and back to ground of the switching FET. This high current path contains nanosecond rise

and fall time and must be kept as short as possible. Therefore, the output capacitor not only must be close to the

VOUT pin, but also to the GND pin to reduce the overshoot at the VOUT pin.

For better thermal performance, TI suggest to make copper polygon connected with each pin bigger.

7.4.2 Layout Example

GND

VOUT

VIN

Input cap

Blue line represents

trace on bottom layer

PFM

PWM

GND

VOUT

Output caps

FB

PVIN

AVIN

VOUT

PG

MODE

EN

SW

Figure 7-2. Layout Example

TPSM81033

SLVSHL0B – JUNE 2024 – REVISED JULY 2024

www.ti.com

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