UCS1003-3 datasheet(43/138 Pages) MICROCHIP

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DS20005346B-page 43

UCS1003-1/2/3

7.0

USB PORT POWER SWITCH

To ensure compliance to various charging specifica-

tions, the UCS1003-1/2/3 family contains a USB port

power switch that supports two Current-Limiting modes:

Trip and Constant-Current (variable slope) modes. The

Current-Limit mode (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).

7.1

Current Limiting

7.1.1

CURRENT LIMIT SETTING

The UCS1003-1/2/3 hardware set current limit (ILIM)

can be one of eight values (see Table 11-1, which

applies to UCS1003-1, and Table 7-1, which applies to

UCS1003-2 and UCS1003-3). This resistor value is

read once upon the UCS1003-1/2/3 devices’ power-up.

In the case of UCS1003-1, 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 hardware current limit (ILIM) and

Communication mode, in the case of UCS1003-1 (Stand-

Alone or SMBus/I2C), 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 11-1.

7.1.2

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 condi-

tion and enter the Error state (see Section 5.1.5 “Error

State Operation”

7.1.3

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 UCS1003-1/2/3 family

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 UCS1003-1/2/3 current limiter will

respond within a specified time (tSHORT_LIM) and will oper-

ate normally at this point. The CBUS capacitor will deliver

the extra current, if any, as required by the load change.

7.1.4

CURRENT-LIMITING MODES

The UCS1003-1/2/3 current limiting has two modes: Trip

and Constant-Current (variable slope) modes. 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 “Detect State Opera-

tion”

), the current capacity at VBUS is limited to

IBUS_BYP, as described in Section 8.2 “VBUS Bypass

Switch”

7.1.4.1

Trip Mode

When using Trip Current-Limiting mode, the

UCS1003-1/2/3 USB port power switch functions as a

low-resistance switch and rapidly turns off if the current

limit is exceeded. While operating using Trip Current-

Limiting mode, the VBUS output voltage will be held

relatively constant (equal to the VS voltage minus the

RON xIBUS current) for all current values up to the ILIM.

If the current drawn by a portable device exceeds ILIM,

the following occurs:

The port power switch will be turned off (Trip

mode action).

The UCS1003-1/2/3 will enter the Error state

and assert the ALERT# pin.

The Fault handling circuitry will then determine

subsequent actions.

TABLE 7-1:

UCS1003-2 AND UCS1003-3

ILIM SELECTION

(1,2)

ILIM Resistor ±5%

ILIM Setting

47 k

 Pull-Down

570 mA

56 k

 Pull-Down

1000 mA

68 k

 Pull-Down

1130 mA

82 k

 Pull-Down

1350 mA

100 k

 Pull-Down

1680 mA

120 k

 Pull-Down

2050 mA

150 k

 Pull-Down

2280 mA

VDD

(if a pull-up resistor is

used, its value must not

exceed 100 k

)

2850 mA

(3000 mA maximum)

Note 1:

Unless otherwise indicated, the values

specified above are the typical ILIM in

Table 1-2.

ILIM pull-down resistors with values less

than 33 k

, connected to UCS1003-2 or

UCS1003-3, will cause unexpected

behavior.

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