PM8801 datasheet(27/37 Pages) STMICROELECTRONICS

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PM8801

PD interface

In the meantime, if the auxiliary voltage fails, the internal regulator takes over without losing

DC/DC control.

The UVLO threshold on VC is 6.0 V typically. At this voltage the DC/DC controller operations

are stopped and the outputs frozen in low state.

While the external auxiliary voltage has to be chosen higher than 8.0 V to take advantage of

the auxiliary winding, it must also be lower than 16 V for all operating conditions, to avoid

the intervention of the internal protection clamp.

A capacitor in the range of 220 nF - 10 µF must be connected to DC/DC ground for stability.

For applications with high current drawn from VC, large capacitance should be used, (e.g.

10 µF) in order to avoid converter switch-off during the startup phase.

A VC UVLO mechanism monitors the level of voltage on the VC pin. When VC voltage

exceeds the VCUVLO_R, the PWM controller is enabled and it remains enabled until the VC

voltage drops below its VCUVLO_F value.

When an auxiliary winding is not used, the internal HV regulator UVLO threshold is set at

6.6 V and the current limit is set at 20 mA typ. This value includes the current internally

drawn to bias the DC/DC controller, the gate drivers, the VB bias regulator and the external

components that may be connected to the VC and VB pins.

Notice that using the HV regulator without the auxiliary winding increases the internal power

dissipation, and when operating at high ambient temperature may lead the device to go into

thermal shutdown.

4.10

5 V bias regulator

The PM8801 features an accurate 5 V output regulator, which can be used to bias the

DC/DC feedback network and the optocoupler connected to the microcontroller.

A capacitor in the range of 100 nF - 2.2 µF must be connected to ARTN for stability.

The regulator current is supplied from the VC pin, to take advantage of the more efficient

bias from the auxiliary winding. This means that the current drawn from the VB pin must be

taken into account to evaluate the maximum current drawn from the VC pin.

The current drawn from the VB pin must be limited to 10 mA maximum.

The VB regulator is also able to accept injected current up to 1 mA without losing voltage

regulation.

PM8801 датащи(PDF) 27 Page - STMicroelectronics