XTAL1

C1

C2

C

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XTAL2

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TUSB2036

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SLLS372H – MARCH 2000 – REVISED JANUARY 2016

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Copyright © 2000–2016, Texas Instruments Incorporated

8.3 Feature Description

8.3.1 USB Power Management

The TUSB2036 supports both bus-powered and self-powered modes. External power-management devices,

such as the TPS2044, are required to control the 5-V power source switching (on/off) to the downstream ports

and to detect an overcurrent condition from the downstream ports individually or ganged. Outputs from external

power devices provide overcurrent inputs to the TUSB2036 OVRCUR pins in case of an overcurrent condition,

the corresponding PWRON pins are disabled by the TUSB2036. In the ganged mode, all PWRON signals

transition simultaneously, and any OVRCUR input can be used. In the nonganged mode, the PWRON outputs

and OVRCUR inputs operate on a per-port basis.

Both bus-powered and self-powered hubs require overcurrent protection for all downstream ports. The two types

of protection are individual-port management (individual-port basis) or ganged-port management (multiple-port

basis). Individual-port management requires power-management devices for each individual downstream port,

but adds robustness to the USB system because, in the event of an overcurrent condition, the USB host only

powers down the port that has the condition. The ganged configuration uses fewer power management devices

and thus has lower system costs, but in the event of an overcurrent condition on any of the downstream ports, all

the ganged ports are disabled by the USB host.

Using a combination of the BUSPWR and EEDATA/GANGED inputs, the TUSB2036 supports four modes of

power management: bus-powered hub with either individual-port power management or ganged-port power

management, and the self-powered hub with either individual-port power management or ganged-port power

management. Texas Instruments supplies the complete hub solution because we offer this TUSB2036 along with

the power-management devices needed to implement a fully USB compliant system.

8.3.2 Clock Generation

The TUSB2036 provides the flexibility of using either a 6-MHz or a 48-MHz clock. The logic level of the MODE

pin controls the selection of the clock source. When MODE is low, the output of the internal APLL circuitry is

selected to drive the internal core of the chip. When MODE is high, the XTAL1 input is selected as the input

clock source and the APLL circuitry is powered down and bypassed. The internal oscillator cell is also powered

down while MODE is high. For 6-MHz operation, TUSB2036 requires a 6-MHz clock signal on XTAL1 pin (with

XTAL2 for a crystal) from which its internal APLL circuitry generates a 48-MHz internal clock to sample the data

from the upstream port. For 48-MHz operation, the clock cannot be generated with a crystal, using the XTAL2

output, since the internal oscillator cell only supports the fundamental frequency. If low-power suspend and

resume are desired, a passive crystal or resonator must be used, although the hub supports the flexibility of

using any device that generates a 6-MHz clock. Because most oscillators cannot be stopped while power is on,

their use prohibits low-power suspend, which depends on disabling the clock. When the oscillator is used, by

connecting its output to the XTAL1 pin and leaving the XTAL2 pin open, its TTL output level cannot exceed 3.6V.

If a 6-MHz oscillator is used, it must be stopped at logic low whenever SUSPND is high. For crystal or resonator

implementations, the XTAL1 pin is the input and the XTAL2 pin is used as the feedback path. A sample crystal

tuning circuit is shown in Figure 5.

are determined using a crystal from Fox Electronics – part number HC49U-6.00MHz 30\50\0±70\20, which means

Figure 5. Crystal Tuning Circuit