FS6407 datasheet(49/111 Pages) NXP

49 / 111 page

NXP Semiconductors

FS6407/FS6408

Figure 33. VCORE buck regulator

6.7.2.1

Light load condition

In order to improve the converter efficiency and avoid any unwanted output voltage increase, VCORE voltage regulator operates in Pulse

Skipping mode during light load condition. The principle is the same as the VPRE implementation described in details in Light load

condition.

6.7.2.2

Current limitation

A current limitation is implemented to avoid uncontrolled power dissipation inside the device (duty cycle control) and limits the current

below ICORE_LIM. The current limitation is banked when the pass transistor is switched ON during TCORE_BLK_LIM to avoid parasite

detection. When ICORE_LIM threshold is reached, the high-side integrated MOSFET is switched OFF. The MOSFET is not switched ON

again before the next rising edge of the switching clock.

The current limitation induces a duty cycle reduction and leads to the VCORE output voltage to fall down gradually, which may cause an

undervoltage condition and bring the device into the Fail-safe state. The current limitation does not switch OFF the regulator.

6.7.2.3

Voltage monitoring

The overvoltage detection switches OFF the regulator. The regulator remains ON in case of undervoltage detection. Diagnostic is reported

in the dedicated register, generate an Interrupt and may bring the application in Fail-safe state depending on the supervisor configuration

(registers INIT SUPERVISOR 1, 2, 3).

6.7.2.4

VCORE efficiency

VCORE efficiency versus current load is given for information based on typical external component criteria described in the table close to

the graph and at two different VCORE voltages (3.3 V, and 1.2 V) covering most of the 32-bit MCU supply range. The efficiency is valid

above 200 mA load on VCORE in order to be in continuous mode in the 2.2 µH inductor. The efficiency is calculated and has to be verified

by measurement at application level. One of the major contributor degrading the efficiency at VCORE = 1.2 V is the external diode during

the recirculation phase. Lower the diode forward voltage (VF) is, the better the efficiency.

FB_CORE

COMP_CORE

VCORE_SNS

L_Vcore

PGND

GND

ESR cap.

<100m

GND

FS6407 Datasheet(PDF) 49 Page - NXP Semiconductors