MAX5079EUD Maxim Integrated Products, MAX5079EUD Datasheet - Page 12

• Manufacturer Part Number: MAX5079EUD
• Description: MOSFET & Power Driver ICs
• Manufacturer: Maxim Integrated Products

Specifications of MAX5079EUD

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

ORing MOSFET Controller with
Ultra-Fast 200ns Turn-Off
5) PS1, PS2, PS3 are present and PS1 goes open.
PS1’s output capacitors discharge and V
below V
potential from V
fast PS1’s output capacitor discharges, N1 is turned off
due to the crossing of the fast- or slow-comparator
reverse voltage threshold. N1’s gate is discharged with
a 2A sink current into GATE (U1), turning off N1 and
isolating PS1 from the BUS. The load-sharing circuit of
PS2 and PS3 will increase PS2 and PS3’s load current
until the total BUS current requirement is satisfied.
6) PS1, PS2, PS3 are present and providing BUS
V
share circuit forces V
will eventually saturate at their current-sharing voltage
range. Now only PS1 has a positive voltage at IN (U1)
with respect to BUS. All OVI inputs will sense the over-
voltage, but only OVP (U1) will be asserted and latched
low. GATE (U1) is pulled to PGND and remains low as
long as V
remains low, however, U1 tries to turn on N1 unless
V
Use OVP (U1) to either drive the cathode of an opto-
coupler to shutdown PS1 from the primary, or fire an
SCR connected between IN (U1) and PGND.
The internal undervoltage lockout monitors V
V
reaches 2.75V. Once powered and V
increase above 2.75V, the external UVLO is monitored.
The external undervoltage lockout feature monitors the
UVLO input and keeps the MAX5079 off (GATE shorted
to PGND) until V
resistive divider from IN to UVLO to GND or from
AUXIN to UVLO to GND to set the external undervolt-
age lockout threshold. We advise setting the external
UVLO ≥ 2.75V when AUXIN is not present.
The MAX5079 has an internal charge pump that pumps
the gate-drive voltage (V
enhance the n-channel ORing MOSFET. The charge
12
BUS
OUT1
AUXIN
current. PS1 loses its feedback signal and goes
into an overvoltage condition.
______________________________________________________________________________________
increases and PS1 is loaded heavily. The current
is actively kept below the undervoltage lockout.
and keeps the MAX5079 off until either voltage
BUS
OVI
. The MAX5079 (U1) senses a negative
≥ 0.6V. When V
UVLO
OUT1
OUT2
is greater than 0.66V. Connect a
to V
Undervoltage Lockout
GATE
BUS
and V
Internal and External
OVI
. Depending upon how
) high enough to fully
drops below 0.6V, OVP
OUT3
IN
Charge Pump
higher and they
and/or V
OUT1
IN
drops
AUXIN
and
pump is divided into two stages, a voltage doubler run-
ning at 70kHz using an external charge-pump capaci-
tor (C
an internal capacitor.
Connect an external capacitor (C
C-. C
When the rising V
> 0.66V), C
external MOSFET’s gate capacitance. The charge-
pump output is controlled by an internal regulator. The
charge-pump output at GATE sources typically 2mA.
This provides enough current drive to turn on a typical
ORing MOSFET in less than 10µs. When (V
reaches the target value (depending on V
pump is switched off (see the Electrical Characteristics
table). Choose C
MOSFET gate capacitance. Too low of a capacitance
will delay the turn-on of the ORing MOSFET, while too
high of a capacitance can cause excessive ripple at
V
avoid ripple at IN caused by the charge-pump switch-
ing. A clamp is placed internally between GATE and IN
to prevent (V
is less than 5V, the charge pump (tripler) will increase
V
ORing MOSFET. The internal charge-pump booster
(voltage tripler) section is operational only when V
V
When an additional supply is connected to AUXIN and
(V
disabled. In this case, the charging of the ORing gate
comes entirely from V
pump flying capacitor can be eliminated and C+, C-
can be left floating.
The MAX5079’s charge pump provides bias to charge
the ORing MOSFET gate above IN (the MOSFET’s
source). GATE source current and the turn-on speed
depends upon the value of C
C+ and C-). Typically GATE can source up to 2mA with
C
above V
capacitance of up to 10nF. With V
can be used for better R
MAX5079 automatically selects the gate-drive voltage for
IN
AUXIN
GATE
EXT
AUXIN
. Bypass IN to GND with a 1µF ceramic capacitor to
EXT
EXT
= 0.1µF. This enables V
to 3x’s V
are low and is turned off when V
IN
- V
), and a voltage tripler running at 1MHz using
is charged from the higher of V
in less than 10µs for an ORing MOSFET gate
IN
EXT
GATE
) > 5V, both charge pumps are completely
GATE Drive and Gate Pulldown
IN
is discharged through GATE into the
IN
- V
EXT
to further reduce the R
becomes greater then V
IN
AUXIN
) from exceeding 11V. When V
equal to 10 times the ORing
DSON
. In this case, the charge-
EXT
GATE
IN
EXT
characteristics. The
(connected between
< 5V, 12V MOSFETs
) between C+ and
to rise to over 2V
IN
IN
exceeds 5V.
IN
DSON
) the charge
BUS
GATE
or V
(V
AUXIN
IN
of the
- V
UVLO
and
IN
IN
)
.