USB3370 datasheet(28/75 Pages) MICROCHIP

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USB3370

DS00001915B-page 28

 2012 - 2015 Microchip Technology Inc.

5.7.3.3

VBUS Input Impedance

The OTG Supplement requires an A-Device that supports Session Request Protocol to have a VBUS input impedance

less than 100kΩ and greater the 40kΩ to ground. The USB3370 provides a 75kΩ resistance to ground, RVB. The RVB

resistor tolerance is detailed in Table 4-8.

5.7.3.4

VBUS Over Voltage Protection (OVP)

The USB3370 provides an integrated over voltage protection circuit to protect the VBUS pin from excessive voltages

that may be present at the USB connector. The over voltage protection circuit works with an external resistor (RVBUS)

by drawing current across the resistor to reduce the voltage at the VBUS pin.

When voltage at the VBUS pin exceeds 5.5V, the Over voltage Protection block will sink current to ground until VBUS

is below 5.5V. The current drops the excess voltage across RVBUS and protects the USB3370 VBUS pin. The required

RVBUS value is dependent on the operating mode of the USB3370 as shown in Table 5-5.

The Over voltage Protection circuit is designed to protect the USB3370 from continuous voltages up to 30V on the

RVBUS resistor.

The RVBUS resistor must be sized to handle the power dissipated across the resistor. The resistor power can be found

using the equation below:

For example, protecting a peripheral or device only application to 15V would require a 20kΩ RVBUS resistor with a power

rating of 0.05W. To protect an OTG product to 15V would require a 1kΩ RVBUS resistor with a power rating of 0.1W.

5.7.4

DRIVING EXTERNAL VBUS

The USB3370 monitors VBUS as described in VBUS Monitoring and VBUS Pulsing. For OTG and Host applications,

the system is required to source 5 Volts on VBUS. The USB3370 fully supports VBUS power control using an external

VBUS switch. The USB3370 provides an open drain active low control signal, CPEN_N, that is dedicated to controlling

the VBUS supply when configured as an A-Device.

CPEN_N

is driven by setting the DrvVbus or DrvVbusExternal bit of the OTG Control register. To be compatible with

Link designs that support both internal and external VBUS supplies, the DrvVbus and DrvVbusExternal bits in the OTG

Control Register are NOR’d together. This enables the Link to set either bit to access the external VBUS enable

(CPEN_N). This logic is shown in Figure 5-9. DrvVbus and DrvVbusExternal are set to 0 on Power On Reset (POR) as

shown in Section 7.1.1.7.

TABLE 5-5:

REQUIRED RVBUS RESISTOR VALUE

Operating Mode

RVBUS

Device only

20kΩ ±5%

OTG Host Capable of less than 100mA of

current on VBUS

1kΩ ±5%

Host or OTG Host capable of >100mA

UseExternalVbusIndicator = 1

20kΩ ±5%

RVBUS

Vprotect

5.0

–

()

VBUS

--------------------------------------------

Where:

• Vprotect is the VBUS protection required.

•RVBUS is the resistor value, 1kΩ or 20kΩ.

•PRVBUS is the required power rating of RVBUS.

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