LTC4240IGN datasheet(12/28 Pages) LINER

12 / 28 page

LTC4240

4240f

used to turn off/on the power switches, turn on the status

LED (alerting the user that its safe to remove the plug-in

board), and assert the LOCAL_PCI_RST# signal. The I2C

bus is also used to read the logic signals of several device

pins: FAULT, PWRGD, RESETIN, and RESETOUT. Addi-

tionally, when a supply generates a current fault, the I2C

bus can be used to determine which supply generated the

fault. See Send Byte and Receive Byte sections for a full

description of all I2C features.

The LTC4240 supports Send Byte and Receive Byte proto-

cols. Communication is achieved using the SCL and SDA

pins (TTL compatible input thresholds). The SCL pin is the

clock input from the I2C bus (host) to the LTC4240 (slave).

The maximum SCL frequency is 100kHz. SDA is the

bidirectional data transfer line between the I2C bus and the

LTC4240. Send Byte and Receive Byte protocols are both

comprised of 2 bytes. The first byte for both is the address

byte. All communication begins with a START command.

Programming the I2C Address

The voltage on the ADDRIN pin determines the I2C ad-

dress. The ADDRIN voltage is set externally with a resistor

divider from 5VIN to ground (resistor placement must be

close to the pin, do not place a bypass capacitor on

ADDRIN). This voltage is fed to a 5-bit A/D and compared

against the address byte clocked in by the I2C bus. The 5-

bit A/D allows 32 unique LTC4240 devices to be connected

on the same I2C bus. 1% resistors should be used to place

the voltage at ADDRIN approximately 0.5 LSB away from

each code transition. Table 1 shows recommended resis-

tor values for each of the address code segments. The

resistor ratio for each code segment has been optimized

for best performance over the specified temperature range.

The parallel resistance for the address setting resistors

should be kept under 10k.

APPLICATIO S I FOR ATIO

Table 1. Suggested ADDRIN 1% Resistor Values

ADDR RECOMMENDED ALLOWED ADDRIN

R19(TOP)

R20(BOT)

CODE ADDRIN VOLTAGE VOLTAGE RANGE

RESISTOR

0.108125

0.080 to 0.136

8660

191

0.264375

0.236 to 0.293

2550

140

0.420625

0.393 to 0.449

2550

237

0.576875

0.549 to 0.605

2550

332

0.733125

0.705 to 0.761

2550

442

0.889375

0.861 to 0.918

2550

549

1.045625

1.018 to 1.074

3830

1020

1.201875

1.174 to 1.230

2550

806

1.358125

1.330 to 1.386

2550

953

1.514375

1.486 to 1.543

1150

499

1.670625

1.643 to 1.699

1020

511

1.826875

1.799 to 1.860

8660

4990

1.983125

1.955 to 2.021

2550

1690

2.139375

2.111 to 2.175

2550

1910

2.295625

2.268 to 2.330

1130

2.451875

2.424 to 2.488

1370

1330

2.608125

2.580 to 2.644

2550

2800

2.764375

2.736 to 2.800

2550

3160

2.920625

2.888 to 2.950

2550

3570

3.076875

3.044 to 3.110

715

1150

3.233125

3.200 to 3.262

1150

2100

3.389375

3.356 to 3.421

1150

2430

3.545625

3.513 to 3.574

1150

2800

3.701875

3.669 to 3.731

357

1020

3.858125

3.825 to 3.886

2550

8660

4.014375

3.981 to 4.041

249

1020

4.170625

4.138 to 4.190

1070

5360

4.326875

4.294 to 4.349

178

1150

4.483125

4.450 to 4.499

133

1150

4.639375

4.606 to 4.651

102

1300

4.795625

4.763 to 4.805

105

2430

4.951875

4.919 to 4.962

100

10000

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