MAX6876 datasheet(21/39 Pages) MAXIM

21 / 39 page

EEPROM-Programmable, Quad,

Power-Supply Tracker/Sequencer Circuit

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command (Table 7). If a latch-on fault mode is chosen,

a toggle on the internal enable clears the latch condi-

tion and restarts the device after a fault condition

(Figure 7).

Reference Voltage Input (REFIN)

The MAX6876 features an internal +1.25V voltage refer-

ence. The voltage reference sets the threshold of the

voltage detectors. Leave REFIN unconnected when

using the internal reference. REFIN accepts an external

reference in the +1.225V to +1.275V range. Use Table

8 commands to select the external reference.

Track Enable Input (TRKEN)

The track enable (TRKEN) monitor input is another fea-

ture of the MAX6876. To enable voltage-tracking

power-up operation, drive TRKEN higher than 1.285V.

When TRKEN goes below 1.25V, OUT_ outputs start

tracking down. Connect TRKEN to an external resistor-

divider network to set the desired monitor threshold.

Connect TRKEN to ABP if not used.

SYNCH

The MAX6876 provides selectable tracking synchro-

nization output or input (SYNCH). SYNCH allows track-

ing of up to 16 power supplies on the same I2C bus.

One device is programmed as the SYNCH master and

the other devices are programmed as slaves. SYNCH

of the master device outputs the common ramp voltage

to which all OUT_ voltages are tracked. The SYNCH

pins of the slave devices are inputs for the ramp control

voltage (no internal ramp is generated in the slave

devices) (see Table 1).

Monitored Outputs

OUT1–OUT4

The MAX6876 monitors four OUT_ outputs to control

the tracking/sequencing performance. After the internal

supply (ABP) exceeds the minimum voltage (2.7V)

requirements, TRKEN > 1.25V, the internal ENABLE

input is logic high, and IN1–IN4 are all within their

selected thresholds, OUT1–OUT4 will begin to track or

sequence.

During power-up mode, the MAX6876 drives the gates

of the external n-channel FETs to force the OUT_ volt-

ages to track the internally set ramp voltage. If OUT_

voltages vary from the ramp voltage by more than

±125mV, an internal comparator signals an alert that

dynamically adjusts the ramp voltage (stops the ramp

until the slow OUT_ catches up). During power-down

mode, an internal pulldown resistor (100

Ω) on OUT_

can be enabled to help discharge load capacitance.

ADDRESS

EEPROM MEMORY

ADDRESS

BIT RANGE

DESCRIPTION

Bit 1—If 1, check ENABLE with I2C enable control bit

If 0, ignore ENABLE with I2C

09h

29h

[1:0]

Bit 0—If 0, enable with I2C = 0, I2C enable command bit

If 1, enable with I2C = 1

Table 7. Program ENABLE

ADDRESS

EEPROM MEMORY

ADDRESS

BIT RANGE

DESCRIPTION

11h

31h

Bit 0—If 1, selects external reference; 0 selects internal reference

Table 8. Select External Reference

ENABLE

INTERNAL

ENABLE

TRKEN

I2C ENABLE CONTROL BIT

(RAM REGISTER)

1 = YES

0 = NO

I2C ENABLE COMMAND BIT

(RAM REGISTER)

0 = OFF

1 = ON

09h[0]

09h[1]

VTRKEN

Figure 7. Logic ENABLE

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