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To create a basic design with the MAX6877, such as the one in Figure 1, follow these steps:
1. Select the input voltage thresholds for IN1, IN2, and IN3. The input voltages must exceed these thresholds for
power-up to begin. Use the following formula to set the resistor-divider values for IN1. (For IN2 or IN3,
replace R
1
with R
3
, or R
5
and R
2
with R
4
or R
6
.)
2. Select the EN/active-low UV threshold using the following formula. EN/active-low UV can also be used as a
logic-level input to control power up. If not used, connect EN/active-low UV to ABP.
3. Set the voltage slew rate. (This is the rate at which the voltages at the outputs OUT1, OUT2, OUT3 ramp up
and down.) Select capacitor C
SLEW
by using the following formula:
where C
SLEW
is in farads, and SR is in V/s. C
SLEW
must be in the range of 100pF < C
SLEW
< 1nF.
4. In sequencing-mode only, the voltages come up one after another, separated by a time delay which is set by
capacitor C
DELAY
using the following formula:
where C
DELAY
is in farads, and t
DELAY
is in seconds. t
DELAY
is also the delay time from when all thresholds are
exceeded to the start of sequencing or tracking. C
DELAY
can be safely left out of the circuit, in which case
t
DELAY
becomes the default 200µs.
5. Pick the MOSFETs for each channel. Ensure that the MAX6877 gate-drive circuit can drive the gate capacitance
of the MOSFET.
Multiple MAX6877 parts can be connected together by connecting the power-good output of the first device to the
enable input (EN/active-low UV) of the next device. For more information, see the data sheet.
Application Note 3918: www.maxim-ic.com/an3918
More Information
For technical support:
www.maxim-ic.com/support
For samples:
www.maxim-ic.com/samples
Other questions and comments:
www.maxim-ic.com/contact
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MAX6877:
QuickView -- Full (PDF) Data Sheet -- Free Samples