STPMIC1APQR datasheet(40/140 Pages) STMICROELECTRONICS

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4.5

Boost converter and power switches

The STPMIC1 integrates boost converter and two power switches, primarily dedicated to supply USB sub-system:

PWR_USB_SW with 500 mA capability PWR_SW with 1 A capability.

For application examples refer to USB sub-system examples.

Figure 48. Boost and switch block diagram

4.5.1

Boost converter

Boost is a synchronous constant on-time step-up converter with fixed 5.2 V output. It is dedicated to power supply

USB sub-system (VBUS) with 1.1 A rated output current to supply up to 3 USB ports: x2 USB host port @500 mA

+ 1 USB OTG port @100 mA.

Boost requires 3 small external components only to operate (1 coil LXB, 2 capacitors CVLXBST and CBSTOUT) –

there is no external diode required. Refer to: Table 2. Passive components.

Input voltage range Converter is capable to supply 0.5 A starting from as low as 2.8 V input, and full rated

current from 3.3 V input. This allows a wide range of applications to be supported embedding USB host port like

Li-Ion/Li-Po battery powered applications or 5 V DC wall adaptor applications.

Bypass feature Boost integrates an advanced bypass circuitry that allows fast and smooth transition to be

performed from boost to bypass operation and reciprocally to keep VBUS in USB compliant tolerance [4.75 V;5.5

V]. This allows USB subsystems to be supplied with standard 5 V DC wall adaptors.

•

When the wall adaptor voltage is below ~5.2 V (due to its nominal tolerance, load regulation or voltage loss

between adaptor and device), the converter works in boost mode

•

When the wall adaptor voltage is between ~5.2 V to 5.5 V (due to its nominal tolerance or light device load),

the converter works in bypass mode

Switching frequency of converter is 2 MHz in steady-state CCM condition for VIN below ~5 V. During load

transient, switching frequency can be temporarily increased/decreased to provide accurate amount of energy

needed and minimize the voltage error. For VIN above ~5.2 V or for low load conditions, 2 MHz frequency

decreases to optimum.

Clock synchronization - The controller integrates PLL circuit, that maintains steady-state frequency in CCM

locked in phase to reference 2 MHz clock generated by the internal oscillator. Boost clock is shifted in phase

to Buck reference clocks, which minimizes the chance of multiple controllers switching at the same time, and

improving EMI performance.

STPMIC1

Boost converter and power switches

DS12792 - Rev 7

page 40/140

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