MAX6876
EEPROM-Programmable, Quad,
Power-Supply Tracker/Sequencer Circuit
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Modes of Operation
The MAX6876 provides three different modes of opera-
tion: tracking, sequencing, and mixed modes. The
mixed mode is a combination of both tracking and
sequencing modes (see the Mixed Mode (Tracking/
Sequencing) section).
Tracking
When all selected inputs exceed their selected thresh-
olds, V
TRKEN
> 1.285V, and ENABLE is logic high, the
tracking process is initialized. The MAX6876 generates
an internal ramp voltage that drives the control loops
for the desired tracked voltage. The tracking functional-
ity is monitored with a comparator control block (see
the Functional Diagram and Figure 5). The comparators
monitor and control each output voltage with respect to
the common tracking ramp voltage to stay within a
±125mV differential window, monitor each tracked out-
put voltage with respect to its input voltage, and moni-
tor each output voltage with respect to GND during
power-up/retry cycles. Under normal conditions each
OUT_ voltage will track the ramp voltage until the OUT_
voltage approximates the IN_ voltage (the external
n-channel FET is saturated). The slew rate for the ramp
voltage is selected through EEPROM.
Master/Slave Operation (Tracking Only)
To support voltage tracking for more than four supplies,
combine multiple MAX6876 devices. Two MAX6876
devices (one master/one slave) track up to eight supply
voltages and four MAX6876 devices (one master and
three slaves) track up to 16 supply voltages. Each
device must be programmed to act in master or slave
mode (only one master is allowed); the default state is
single device (see Table 1). The MAX6876 outputs the
ramp control voltage with the SYNCH output when con-
figured as a master device. This ramp allows multiple
devices to synchronize with the master when slave
SYNCHs are configured as inputs. For proper function-
ality control, connect all ENABLE pins together. In mas-
ter/slave mode, all controlled supplies are tracked
up/down (no mixed sequencing/tracking modes are
supported). In master-slave application, the part is
intended to provide only tracking for the four supplies
(only one ramp is generated). To control one particular
channel, insert a “1” in any of the four possible posi-
tions (one row for each channel contains 4 bits) and the
circuit will generate the proper signals (see Figure 6).
For multiple MAX6876 operations, the ramp control volt-
age is brought out of the master’s SYNCH (programmed
as an output) and into the slave’s SYNCH (programmed
as an input). The highest tracked supply must be con-
nected to one of the master’s IN_ inputs. When all IN_
threshold conditions are met (on master and slaves), the
master ramp begins rising at the selected ramp slew rate.
During normal operation all OUT_ voltages (for master
and slave) track the ramp voltage. If the slave’s OUT_
voltages do not properly follow the ramp voltage (exceed
125mV differential), the slave device asserts HOLD low.
The master recognizes the HOLD and holds the ramp
voltage, allowing the slave’s slower OUT_ voltages to
