Technical Note

10/14

BU90002GWZ, BU90003GWZ, BU90004GWZ, BU90005GWZ, BU90006GWZ

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Target spec. ver.1.7

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●Functional descriptions

The BU9000XGWZ are a synchronous step-down DC/DC converter that achieves fast transient response from light load to

heavy load by hysteretic PWM control system and current constant PFM control system.

○PWM control

BU9000XGWZ operates by hysteretic PWM control. This scheme ensures fast switching, high efficiency, and fast transient

response.

When the output voltage is below the VREF voltage, the error comparator output is low to high and turning on P-channel

MOSFET until above the VREF voltage and minimum on time.

○PFM control

At light load the regulator and MODE=low, the regulator operates with reduced switching frequency and improves the efficiency.

During PFM operation, the output voltage slightly higher than typical output voltage.

Fig. Operation of PFM mode and PWM mode

PFM (constant current)Threshold. turn off Pch FET

output PWM mode voltage

PFM Mode at Light Load

PFM Threshold. turn on PFET

PWM Mode at Moderate to Heavy Loads