UCS1002-2 datasheet(48/114 Pages) MICROCHIP

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Programmable USB Port Power Controller with Charger Emulation

Datasheet

Revision 1.4 (07-16-13)

SMSC UCS1002

DATASHEET

Chapter 7 USB Port Power Switch

7.1

USB Port Power Switch

To assure compliance to various charging specifications, the UCS1002 contains a USB port power

switch that supports two current limiting modes: trip and constant current (variable slope). The current

limit (ILIM) is pin selectable (and may be updated via the register set). The switch also includes soft

start circuitry and a separate short circuit current limit.

The port power switch is on in the Active state (except when VBUS is discharging).

7.2

Current Limiting

7.2.1

Current Limit Setting

The UCS1002 hardware set current limit, ILIM, can be one of eight values (see Table 4.1, "UCS1002

Communication Mode and ILIM Selection"). This resistor value is read once upon UCS1002 power-

up.The current limit can be changed via the SMBus / I2C after power-up; however, the programmed

current limit cannot exceed the hardware set current limit.

At power-up, the communication mode (Stand-alone or SMBus / I2C) and hardware current limit (ILIM)

are determined via the pull-down resistor (or pull-up resistor if connected to VDD) on the COMM_SEL

/ ILIM pin, as shown in Table 4.1.

7.2.2

Short Circuit Output Current Limiting

Short circuit current limiting occurs when the output current is above the selectable current limit (ILIMx).

This event will be detected and the current will immediately be limited (within tSHORT_LIM time). If the

condition remains, the port power switch will flag an Error condition and enter the Error state (see

Section 5.1.5, "Error State Operation").

7.2.3

Soft Start

When the PWR_EN control changes states to enable the port power switch, or an Attach Detection

event occurs in the Detect power state and the PWR_EN control is already enabled, the UCS1002

invokes a soft start routine for the duration of the VBUS rise time (tR_BUS). This soft start routine will

limit current flow from VS into VBUS while it is active. This circuitry will prevent current spikes due to

a step in the portable device current draw.

In the case when a portable device is attached while the PWR_EN pin is already enabled, if the bus

current exceeds ILIM, the UCS1002 current limiter will respond within a specified time (tSHORT_LIM)

and will operate normally at this point. The CBUS capacitor will deliver the extra current, if any, as

required by the load change.

7.2.4

Current Limiting Modes

The UCS1002 current limiting has two modes: trip and constant current (variable slope). Either mode

functions at all times when the port power switch is closed. The current limiting mode used depends

on the Active state mode (see Section 9.9, "Current Limit Mode Associations"). When operating in the

Detect power state (see Section 5.1.3), the current capacity at VBUS is limited to IBUS_BYP as

described in Section 8.2, "VBUS Bypass Switch".

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