USB3450

DS00002105A-page 20

5.6

Internal Regulators and POR

The USB3450 includes an integrated set of built in power management functions. These power management features

include a POR generation and allow the USB3450 to be powered from a single 3.3 volt power supply. This reduces the

bill of materials and simplifies product design.

5.6.1

INTERNAL REGULATORS

The USB3450 has two internal regulators that create two 1.8V outputs (labeled VDD1.8 and VDDA1.8) from the 3.3volt

power supply input (VDD3.3). Each regulator requires an external 4.7uF +/-20% low ESR bypass capacitor to ensure

stability. X5R or X7R ceramic capacitors are recommended since they exhibit an ESR lower that 0.1ohm at frequencies

greater than 10kHz.

The specific capacitor recommendations for each pin are detailed in Table 2-1, “USB3450 Pin Definitions,” on page 7,

and shown in FIGURE 6-9: USB3450 Application Diagram (Top View) on page 32.

5.6.2

POWER ON RESET (POR)

The USB3450 provides an internal POR circuit that generates a reset pulse once the PHY supplies are stable. The

UTMI+ Digital can be reset at any time with the RESET pin.

Note:

The USB3450 regulators are designed to generate a 1.8 volt supply for the USB3450 only. Using the reg-

ulators to provide current for other circuits is not recommended and Microchip does not ensure USB per-

formance or regulator stability.