UCS2112 datasheet(28/64 Pages) MICROCHIP

28 / 64 page

UCS2112

DS20005424B-page 28

 2015 Microchip Technology Inc.

Figure 7-1 shows operation of current limits in trip

mode with the shaded area representing the USB 2.0

specified VBUS range. Dashed lines indicate the port

power switch output will go to zero (e.g., trip) when

ILIM is exceeded. Note that operation at all possible

values of ILIM are shown in Figure 7-1 for illustrative

purposes only; in actual operation only one ILIM can be

active at any time.

FIGURE 7-1:

Current Limiting in Trip Mode.

7.1.4.2

Constant Current Limiting (Variable

Slope)

Constant current limiting is used when the current

drawn is greater than ILIM (and ILIM < 1.6A). In CC

mode, the port power switch allows the attached porta-

ble device to reduce VBUS output voltage to less than

the input VS voltage while maintaining current delivery.

The V/I slope depends on the user set ILIM value. This

slope is held constant for a given ILIM value.

This mode is specifically provided for devices that rely

on resistive means to reduce VBUS voltage for direct

battery charging or to allow portable devices a means

to “test” charger capacity. See Figure 7-2.

FIGURE 7-2:

Constant Current Example.

Figure 7-3 shows operation of current limits while

using CC mode. Unlike trip mode, once IBUS current

exceeds ILIM, operation continues at a reduced voltage

and increased current. Note that the shaded area rep-

resenting the USB 2.0 specified VBUS range is now

restricted to an upper current limit of IBUS_R2MIN. Note

that the UCS2112 will heat up along each load line as

voltage decreases. If the internal temperature exceeds

the TREG or TTSD thresholds, the port power switch will

open. Also note that when the VBUS voltage is brought

low enough (below VBUS_MIN), the port power switch

will open.

FIGURE 7-3:

Current Limiting in CC Mode.

7.2

USB Port Power Profiles

The UCS2112 combines the qualities of traditional

USB port power switches with USB port power profiles

set forth in the USB-IF BC1.2 specification. USB port

power profiles consist of distinct voltage-current oper-

ation regions defined by “keep-out” and “operation”

regions.

While operating in the CC mode of operation, the

UCS2112 provides voltage-current output operating

profiles that are specified by two keep-out regions.

If the current reaches the IBUS_R2MIN setting for longer

than tMASK, the UCS2112 enters the Error state and an

Overcurrent event is flagged.

If the VBUS voltage ever goes below the no operation

lower-voltage keep-out (VBUS_MIN) value for longer

than tMASK, the port power switch is disabled and a

keep-out

violation is

flagged

(by

setting

the

MIN_KEEP_OUT status bit). This will cause the device

to enter the Error state.

Figure 7-4 illustrates the relationship between these

USB port power profile parameters.

0.53

1.07

1.6

2.67

3.2

5.25

4.75

IBUS (Amps)

Operating

Current

0.96

1.28

1.07

0.96

0.53

1.6

3.2

2.13

2.67

= ILIM’s

2.13

Power Switch Voltage and Current

Output go to Zero when ILIM is

Exceeded

Trip action

(ILIM = 0.53 A)

Trip action

(ILIM = 3.2 A)

ILIM (Amps)

Control Loop

Temp

GND

ILIM

Power

Switch

Battery

Charger

VBAT

RSense

IBUS

Portable Device

VBUS << VS

UCS 2112

0.53

1.6

2.67

3.2

5.25

4.75

0.96

1.28

0.96

0.53

1.6

IBUS_R2MIN

2.13

2.67

3.2

IBUS (Amps)

ILIM (Amps)

= ILIM’s

Constant resistance

IBUS operation line 1

(ILIM = 0.53 A)

Constant resistance

IBUS operation line 4

(ILIM = 1.6 A)

CC Mode - Power switch current increases as voltage decreases

when ILIM is exceeded following constant resistance lines

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