FS6407 datasheet(50/111 Pages) NXP

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NXP Semiconductors

FS6407/FS6408

Figure 34. VCORE efficiency

6.7.3

Charge pump and bootstrap

Both switching MOSFETs of VPRE and VCORE SMPS are driven by external bootstrap capacitors. Additionally, a charge pump is

implemented to ensure 100% duty cycle for both converters. Each converter uses a 100 nF external capacitor minimum to operate

properly.

6.7.4

VCCA voltage regulator

VCCA is a linear voltage regulator mainly dedicated to supply the MCU I/Os, especially the ADC. The output voltage is selectable at 5.0 V

or 3.3 V. Since this output voltage can be used to supply MCU I/Os, the output voltage selection is done using an external resistor

connected to the SELECT pin and ground if VAUX is used. When VAUX is not used, the resistor is connected between the SELECT pin

and VPRE.

When VCCA is used with the internal MOS transistor, VCCA_E pin must be connected to VPRE. The voltage accuracy is

±1.0% for 5.0 V

configuration and

±1.5% for 3.3 V configuration with an output current capability at 100 mA.

When VCCA is used with an external PNP transistor to boost the current capability up to 300 mA, the connection is detected automatically

during the start-up sequence of the FS6407/FS6408. In such condition, the internal pass transistor is switched OFF and all the current is

driven through the external PNP to reduce the internal power dissipation. The output voltage accuracy with an external PNP is reduced

±3.0% at 300 mA current load. The VCCA output voltage is used as a reference for the auxiliary voltage supply (VAUX) when VAUX is

configured as a tracking regulator.

6.7.4.1

Current limitation

A current limitation is implemented to avoid uncontrolled power dissipation of the internal MOSFET or external PNP transistor. By default,

the current limitation threshold is selected based on the auto detection of the external PNP during start up phase.

• When the internal MOSFET transistor is used, the current is limited to ICCA_LIM_INT and the regulator is kept ON

• When the external PNP transistor is used, the current is limited to ICCA_LIM_OUT and the regulator is switch OFF after a dedicated

duration TCCA_LIM_OFF under current limitation. A SPI command is needed to restart the regulator.

In case of external PNP configuration only, the lowest current limitation threshold can be selected by SPI in the register INIT VREG 2

instead of the highest one. In order to limit the power dissipation in the external PNP transistor in case of short circuit to GND of VCCA

pin, a current limitation foldback scheme is implemented to reduce the current limitation to ICCA_LIM_FB when VCCA is below VCCA_LIM_FB.

FS6407 Datasheet(PDF) 50 Page - NXP Semiconductors