MCP2200T-ISLASHSS datasheet(6/44 Pages) MICROCHIP

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MCP2200

DS20002228C-page 6

 2011-2015 Microchip Technology Inc.

1.5.2.1

Internal Power Supply Details

MCP2200 offers various options for power supply. To

meet the required USB signaling levels, the MCP2200

device incorporates an internal LDO used solely by the

USB transceiver in order to present the correct D+/D-

voltage levels.

Figure 1-2 shows the internal connections of the USB

transceiver LDO in relation to the VDD power supply

rail. The output of the USB transceiver LDO is tied to

the VUSB line. A capacitor connected to the VUSB pin is

required if the USB transceiver LDO provides the 3.3V

supply to the transceiver.

FIGURE 1-2:

MCP2200 INTERNAL

POWER SUPPLY DETAILS

The provided VDD voltage has a direct influence on the

voltage levels present on the GPIO pins (Rx/Tx and

RTS/CTS). When VDD is 5V, all of these pins will have

a logical ‘1’ around 5V with the variations specified in

Section 3.1 “DC Characteristics”.

For applications that require a 3.3V logical ‘1’ level,

VDD must be connected to a power supply providing

3.3V voltage. In this case, the internal USB transceiver

LDO cannot provide the required 3.3V of power. It is

necessary to also connect the VUSB pin to the 3.3V

power supply rail. This way, the USB transceiver is

powered-up directly from the 3.3V power supply.

1.5.2.2

USB Bus-Powered (5V)

In Bus Power Only mode, all power for the application

is drawn from the USB (Figure 1-3). This is effectively

the simplest power method for the device.

FIGURE 1-3:

BUS POWER ONLY

In order to meet the inrush current requirements of the

USB 2.0 specifications, the total effective capacitance

appearing across VBUS and ground must be no more

than 10 µF. If it is not more than 10 µF, some kind of

inrush current limiting is required. For more details on

inrush current limiting, consider the latest version of the

“Universal Serial Bus Specification”

According to the USB 2.0 specification, all USB devices

must also support a low-power Suspend mode. In the

USB Suspend mode, devices must consume no more

than 500 µA (or 2.5 mA for high-powered devices that

are remote wake-up capable) from the 5V VBUS line of

the USB cable.

The host signals the USB device to enter Suspend

mode by stopping all USB traffic to that device for more

than 3 ms.

The USB bus provides a 5V voltage. However, the USB

transceiver requires 3.3V for the signaling (on the D+

and D- lines).

During USB Suspend mode, the D+ or D- pull-up

resistor must remain active, which will consume some

of the allowed suspended current budget (500 µA/

2.5 mA). The VUSB pin is required to have an external

bypass capacitor. It is recommended that the capacitor

be a ceramic capacitor between 0.22 µF. and 0.47 µF.

Figure 1-4 shows a circuit where MCP2200’s internal

LDO is used to provide 3.3V to the USB transceiver.

The voltage on the VDD affects the voltage levels onto

the GPIO pins (Rx/Tx and RTS/CTS). With VDD at 5V,

these pins will have a logic ‘1’ of 5V with the variations

specified in Section 3.1 “DC Characteristics”.

LDO

3.3V

USB

Transceiver

D+

VDD

VUSB

D-

OUT

VDD

VUSB

VSS

VBUS

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