UCS2112 datasheet(27/64 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS20005424B-page 27

UCS2112

7.0

USB PORT POWER SWITCH

assure

compliance

various

charging

specifications, the UCS2112 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).

7.1

Current Limiting

7.1.1

CURRENT LIMIT SETTING

The UCS2112 hardware set current limit, ILIM, can be

one of eight values. This resistor value is read once

upon UCS2112 power-up. The current limit can be

changed via the SMBus/I2C after power-up; however,

the programmed current limit cannot exceed the hard-

ware set current limit. Unless connected to VDD, the

resistors in Table 7-1 are pull-down resistors.

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 resis-

tor if connected to VDD) on the COMM_ILIM pin, as

shown in Table 7-1.

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 imme-

diately be limited (within tSHORT_LIM time). If the condi-

tion remains, the port power switch will flag an Error

condition and enter the Error state.

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 UCS2112 invokes a soft start rou-

tine 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 UCS2112 current limiter will respond

within a specified time (tSHORT_LIM) and will operate nor-

mally 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 UCS2112 current limiting has two modes: trip and

constant current (variable slope). Either mode func-

tions at all times when the port power switch is closed.

When operating in the Detect power state, the current

capacity at VBUS is limited to IBUS_BYP as described in

Section 6.1.1 “VBUS Bypass Switch”

7.1.4.1

Trip Mode

When using trip current limiting, the UCS2112 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, 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

action).

The UCS2112 will enter the Error state and

assert the ALERT# pin.

The fault handling circuitry will then determine

subsequent actions.

Note:

If a load that draws between 2 mA and 7 mA

is connected to the port power switch, a volt-

age ripple between 40-90 mVPP is observed

at the VBUS output. This behavior is normal

and it does not affect the charging process

when a portable device is connected.

TABLE 7-1:

ILIM DECODE

COMM_ILIM

Pulldown

Resistor

(±1%)

PWR_EN1

and

PWR_EN2

Polarity

ILIM (A)

Total ILIM

(A)

(Note 1)

GND

Active-High

0.53

0.53+0.53

10 kΩ

Active-High

0.96

0.96+096

12 kΩ

Active-High

1.07

1.07+1.07

15 kΩ

Active-High

1.28

1.28+1.28

18 kΩ

Active-High

1.6

1.6+1.6

22 kΩ

Active-High

2.13

2.13+2.13

27 kΩ

Active-High

2.67

2.67+2.67

33 kΩ

Active-High

3.2

3.2+3.2

47 kΩ

Active-Low

0.53

0.53+0.53

56 kΩ

Active-Low

0.96

0.96+0.96

68 kΩ

Active-Low

1.07

1.07+1.07

82 kΩ

Active-Low

1.28

1.28+1.28

100 kΩ

Active-Low

1.6

1.6+1.6

120 kΩ

Active-Low

2.13

2.13+2.13

150 kΩ

Active-Low

2.67

2.67+2.67

VDD

Active-Low

3.2

3.2+3.2

Note 1:

The total maximum current depends on

power dissipation characteristics of the

design (see Table 1-1).

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