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DS00001824A-page 13

USB375x

4.1

VBUS Protection Switch

The USB375x protects the entire system from errant VBUS voltages, whether over-voltage or under-voltage conditions.

The device is able to dynamically monitor the VBUS voltage levels and take appropriate action by opening the integrated

VBUS Protection Switch when these errant conditions occur. Specifically, when VBUS is below the Under Voltage Lock-

Out (UVLO) level or above the Over Voltage Lock-Out (OVLO) level, the VBUS switch will open thereby disconnecting

the VBUS pin from VOUT. See Section 3.3 for UVLO and OVLO timing diagrams. Manual control of the VBUS Switch,

4.1.1

100MA CURRENT LIMIT (USB375X-1 ONLY)

bit The USB375x-1 provides a 100mA current limit feature which allows a portable system with a dead battery to still

draw 100mA from a compliant host. When plugged into a Standard Downstream Port (SDP), the USB375x-1 will enable

plugged into any other charger, the USB375x-1 will enable the 100mA current limit during charger detection, and will

disable the 100mA current limit once charger detection has completed. Figure 4-6 details the charger detection flow of

the USB375x-1.

4.2

Charger Detection

The USB375x includes the circuitry required to implement the USF-IF Battery Charging Specification (revision 1.2). The

USB375x will automatically perform a charger detection upon start-up. The USB375x includes a state machine to pro-

vide the detection of a wide variety of USB charger detection methods listed in Table 4-1. When any of the USB chargers

are plugged into the system, the USB375x will detect a charger plug in event, determine what type of charger it is, and

mentioned above. The second is through the INT_B pin. When a compliant charger is plugged in and detected, the

USB375x will automatically drive the INT_B signal low. Figure 4-4 details the automatic charger detection flow of the

USB3750-1, Figure 4-5 details the automatic charger detection flow of the USB3751-1, and Figure 4-6 details the auto-

matic charger detection flow of the USB3751-2.

FIGURE 4-2:

USB3751 BLOCK DIAGRAM

SCL

SDA

VBUS

VOUT

I

Interface

INT_B

DP

DM

USB 2.0 PHY,

Processor, or

Accessory

Processor

Charger

Detection

Battery

Charger/

PMU

GND

DM_1

DP_1

Over-Voltage/Under-Voltage

Protection and Current

Limiting

VBUS

VBUS

DP

DM

USB3751