AS3517H-ECTP datasheet(44/94 Pages) AMSCO

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AS3517 V17

Data Sheet, Confidential

www.austriamicrosystems.com

9.2.5

USB VBUS Supply

The VBUS voltage converter consists out of a charge pump and a DCDC converter. These 2 blocks share common pins. The charge

pump (CP) and is used as USB-OTG (on the go) supply (5V/8mA) and the DCDC step-up converter provides the USB-HOST supply (5V

/500mA). Depending on the external configuration either CP mode or DCDC mode is selected. Be aware that only one block can be used

in one application. The following description shows how each block operates and how the circuit should be configured.

Additional the USB VBUS generation block features a VBUS comparator to detect different VBUS levels thus complies to SRP (session

request protocol) and HNP (host negotiation protocol).

VBUS DCDC (USB Host Supply)

With the pin USBH_CSP connected to the battery voltage the mode USB-HOST mode is selected. This means the DCDC converter

supplies 5V and up to 500mA.

For device safety an external PMOS switch is necessary in the case of a short-circuit condition on the VBUS pin. With this PMOS the

device can shut off the path between battery and output. During start-up the PMOS switch will be opened very slowly by discharging his

gate with a small current sink. Depending on the value of the Gate-Source Capacitance and the start-up time, different current values for

the current sink can be programmed.

During start-up and operation the DCDC also monitors the current over the sense resistor. If the current limit will be reached during start-

up the DCDC will generate an interrupt signal after 5.3usec de-bounce time. If this over-current condition is still present after 85µs the

DCDC converter will be shut off by resetting its register. During start-up, however, an interrupt will be masked until pin USBH_PG is lower

than 1V.

Figure 27 VBUS DCDC Block Diagram

Revision 1v3

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