SC900A 查看數據表（PDF） - Semtech Corporation

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SC900A

Programmable Penta ULDO with RESET and I2C Interface

Semtech Corporation 

SC900A

POWER MANAGEMENT

Applications Information (Cont.)

Active Shutdown

The shutdown control bits determine how the on-chip ac-

tive shutdown switches behave. Each LDO register uses

bit 5 of the LDO output voltage data byte to control the

shutdown behavior. When the active shutdown bit is en-

abled (set to 1), the capacitance on the LDO output will be

discharged by an on-chip FET after the LDO is disabled.

When the active shutdown bit is disabled (set to 0), the

output capacitance on the LDO output is discharged by

the load. The default active shutdown state for all LDOs

is on.

ON/OFF Control Register

Each individual LDO may be turned on or off by accessing

the ON/OFF control register. LDOs are turned on by set-

ting their respective on/off bit to 1. Likewise, they can be

turned off by setting the on/off bit to 0. This allows for

on/off control with a single write command. If the enable

(EN) pin is high and data is written to the LDO voltage reg-

isters, the LDO outputs will go to the voltage prescribed by

the Output Voltage Code bits (0-4). Data will not be lost

when toggling the on/off bit from 0 to 1. However, if the

EN pin is forced low, all circuitry in the device is disabled.

All programmed information is lost when the enable bit is

subsequently pulled high.

VASEL Pin

The VASEL pin sets the default voltage of LDO A, the core

supply. When this pin is set to VIN, the default voltage is

2.80V. When this pin is set to GND, the default voltage is

1.80V. The voltage can be changed from its default state

after start up by writing to the LDO voltage code register.

When the A0 pin is tied to GND, device 1 has an address

of 0 and the combination of device type ID and address is

0x08H. When the A0 pin is tied to VIN, device 2 has and

address of 1 and the combination of device type ID and

address is 0x09H.

The last bit of the slave address defines the operation to

be performed. When set to a one a read operation is se-

lected; when set to a zero a write operation is selected.

Following a start condition, the SC900A monitors the SDA

line comparing the slave address being transmitted with

its slave address (device type ID and state of A0 input).

Upon a correct compare the SC900A outputs an acknowl-

edge on the SDA line. Depending on the state of the R/W

bit, the SC900A will execute a read or write operation.

Protection Circuitry

The SC900A provides protection circuitry that prevents

the device from operating in an unspecified state. These

include Under Voltage Lockout Protection, Over-tempera-

ture Protection and Short-circuit Protection.

Under Voltage Lockout

The SC900A provides an Under Voltage Lockout (UVLO)

circuit to protect the device from operating in an unknown

state if the input voltage supply is too low. When the bat-

tery voltage drops below the UVLO threshold, the LDOs

are disabled. As the battery voltage increases above the

hysteresis level, the LDOs are re-enabled into their previ-

ous states, provided ENABLE has remained high. If EN-

ABLE goes low, the SC900A will shut down.

Device Addressing

Following a start condition, the master must output the

address of the slave it is accessing. The most significant

six bits of the slave are the device type identifier (ID). For

the SC900A this is fixed at 000100[B]. The next signifi-

cant bit addresses a particular device. A system can have

up to two SC900A devices on the bus. The two addresses

are defined by the state of the A0 input (see Figure 1).

Over Temperature Protection

The SC900A provides an internal Over-temperature (OT)

protection circuit that monitors the internal junction tem-

perature. When the temperature exceeds the OT thresh-

old, the OT protection disables all the LDO outputs. As

the junction temperature drops below the hysteresis level

the OT protection re-enables all the LDOs in their previous

states, provided ENABLE has remained high. If ENABLE

goes low, the SC900A will shut down.

DEVICE TYPE IDENTIFIER

0

0

0

1

0

0

DEVICE ADDRESS

Pin A0 to GND = 0

Pin A0 to VIN = 1

R/W

X

Short-Circuit Protection

Each LDO output has short-circuit protection. If a short is

applied to any output, the output voltage will drop and the

Figure 1 - Slave Address Structure

output current will be limited to the short circuit current

until the short is removed.

© 2005 Semtech Corp.

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