MAX4840 MAXIM [Maxim Integrated Products], MAX4840 Datasheet - Page 6

• Manufacturer Part Number: MAX4840
• Description: Overvoltage Protection Controllers with Status FLAG
• Manufacturer: MAXIM [Maxim Integrated Products]

Overvoltage Protection Controllers with
Status FLAG
Figure 5. Functional Diagram
The MAX4838–MAX4841 provide up to 28V overvoltage
protection for low-voltage systems. When the input volt-
age exceeds the overvoltage trip level, the MAX4838–
MAX4841 turn off a low-cost external N-channel FET(s)
to prevent damage to the protected components. An
internal charge pump
a simple, robust solution.
The MAX4838–MAX4841 have a fixed 3.25V typical
undervoltage lockout level (UVLO). When V
than the UVLO, the GATE driver is held low and FLAG
is asserted.
The MAX4838/MAX4839 have a 7.4V typical overvolt-
age threshold (OVLO), and the MAX4840/MAX4841
have a 5.8V typical overvoltage threshold. When V
greater than OVLO, the GATE driver is held low and
FLAG is asserted.
The FLAG output is used to signal the host system
there is a fault with the input voltage. FLAG asserts
immediately to an overvoltage fault. FLAG is held low
for 50ms after GATE turns on before deasserting.
The MAX4839 and MAX4841 have a push-pull FLAG out-
put. The output high voltage is proportional to V
up to 5.5V, and fixed at 5.5V when V
The MAX4838 and MAX4840 have an open-drain FLAG
output. Connect a pullup resistor from FLAG to the
logic I/O voltage of the host system.
EN is an active-low enable input on the MAX4838 and
MAX4840 only. Drive EN low or connect to ground to
6
_______________________________________________________________________________________
Undervoltage Lockout (UVLO)
Overvoltage Lockout (OVLO)
(Figure
Detailed Description
GND
EN
IN
5) drives the FET gate for
EN Enable Input
IN
> 5.5V.
FLAG Output
REGULATOR
DETECTOR
UVLO AND
OVLO
5.5V
IN
IN
is less
for V
IN
IN
is
LOGIC AND TIMER
2x CHARGE
CONTROL
PUMP
enable normal device operation. Drive EN high to force
the external MOSFET(s) off. EN does not override an
OVLO or UVLO fault.
An on-chip charge pump is used to drive GATE above
IN, allowing the use of low-cost N-channel MOSFETS.
The charge pump operates from the internal 5.5V
regulator.
The actual GATE output voltage tracks approximately
two times V
level is exceeded, whichever comes first. The
MAX4838/MAX4839 have a 7.4V typical OVLO, there-
fore GATE remains relatively constant at about 10.5V
for 5.5V < V
5.8V typical OVLO, but this can be as low as 5.5V. The
MAX4840/MAX4841 in practice may never actually
achieve the full 10.5V GATE output. The GATE output
voltage as a function of input voltage is shown in the
Typical Operating Characteristics.
The MAX4838–MAX4841 have an on-board state
machine to control device operation. A flowchart is
shown in
if V
If UVLO < V
startup after a 50ms internal delay. The internal charge
pump is enabled, and GATE begins to be driven above
V
ing startup until the FLAG blanking period expires, typi-
cally 50ms after the GATE starts going high. At this
point the device is in its on state.
At any time if V
low and GATE is driven to ground.
IN
IN
by the internal charge pump. FLAG is held low dur-
> OVLO, GATE is held at 0V, and FLAG is low.
Figure
GATE DRIVER
IN
IN
IN
MAX4838–
MAX4841
< OVLO and EN is low, the device enters
until V
< 7.4V. The MAX4840/MAX4841 have a
IN
6. On initial power-up, if V
drops below UVLO, FLAG is driven
IN
exceeds 5.5V or the OVLO trip
GATE
FLAG
Device Operation
GATE Driver
IN
< UVLO or