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1/18/2017

2016-11-0004

PT0493-4

22

PI5USB2546

Implementing Power Wake in Notebook System

An implementation of power wake in notebook platforms with the PI5USB2546 is shown as below. Power wake function is

used to select between a high power DC-DC converter and low power LDO (100mA) based on charging requirements. System

power saving is achieved when under no charging conditions (the connected device is fully charged or no device is connected)

the DC-DC converter is turned-off (to save power since it is less efficient in low power operating region) and the low power

LDO supplies standby power to the charging port.

Power wake is activated in S4/S5 mode (0011 setting, see device truth table), PI5USB2546 is charging connected device as

shown as case 1, /STATUS is pulled LOW (Case 1) which switches-out the LDO and switches-in the DC-DC converter to

handle high current charging.

Figure 7, Case 1: System in S4/S5, Device Charging

As shown in Case 2A (Figure 8) and Case 2B (Figure 9), when connected device is fully charged or gets disconnected from the

charging port, the charging current will fall. If charging current falls to <45mA and stays below this threshold for over 15s,

PI5USB2546 automatically sets a 55mA internal current limit and /STATUS is de-asserted (pulled HI). As shown in Case 2A

and Case 2B. This results in DC-DC converter turning off and the LDO turning on. Current limit of 55mA is set to prevent the

low power LDO output voltage from collapsing in case there is a spike in current draw due to device attachment or other

activity such as display panel LED turning ON in connected device.

Following Power Wake flow chart when a device is attached and draws >55mA of charging current the PI5USB2546 will hit its

internal current limit. This will trigger the device to assert /STATUS (LO) and turn on the DC-DC converter and turn off the

LDO. PI5USB2546 will discharge OUT for >2s (typ.) to allow the main power supply to turn on. After the discharge the device

will turn back on with current limit set by ILIM_HI (Case 1, Figure 7)

Peripheral

Device

Charging

LDO Disconnected/Shut-Down

DC-DC Switch-In

Note: DC/DC and LDO switch

based on STATUS.

Power Block

19V

EN

EN

5V DC/DC

5V LDO

IN

System

Controller

DM

DP

OC

I/O_EN

STATUS

FAULT

DM_OUT

DP_OUT

EN

CTL1

CTL2

CTL3

ILIM_SEL

PI5USB2546

OUT

DM_IN

DP_IN

GND

ILIM_LO

ILIM_HI

VBUS

D-

D+

GND

0011

1

Ilimit set by

Rlim_hi