MAX6399 MAXIM [Maxim Integrated Products], MAX6399 Datasheet - Page 6

• Manufacturer Part Number: MAX6399
• Description: High-Voltage, Overvoltage/Undervoltage, Protection Switch Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX6399 includes internal thermal-shutdown pro-
tection, disabling the external MOSFET if the device
reaches overtemperature conditions.
The MAX6399 active-low SHDN input turns off the exter-
nal MOSFET, disconnecting the load and reducing
power consumption. After power is applied and SHDN
is driven above its logic-high voltage, there is a 100µs
delay before GATE begins to enhance. SHDN is also uti-
lized to unlatch GATE after an overvoltage condition has
been removed.
The MAX6399 uses a high-efficiency charge pump to
generate the GATE voltage. Upon V
5V (typ) UVLO threshold, GATE enhances 10V above
IN (for V
voltage condition occurs when the voltage at SET pulls
above its 0.5V threshold. When the overvoltage fault
occurs (SET = 0.5V), GATE latches off, which discon-
nects the load from the power source (see Figure 2).
After the overvoltage fault has disappeared, the fault
can be unlatched by toggling SHDN or recycling the
MAX6399 input.
The MAX6399 overvoltage protection features a fast com-
parator that disconnects the load from the main power
line when an overvoltage condition occurs at the output of
a DC-DC converter. When an overvoltage condition is
sensed, the MAX6399 latches GATE off, disconnecting
the power source from the DC-DC input. To unlatch
GATE after an overvoltage fault has disappeared, recycle
IN or toggle SHDN.
SET provides an accurate means of monitoring a sys-
tem voltage for an overvoltage fault. Use a resistor-
divider network to set the desired overvoltage condition
(Figure 2). SET has a rising 0.5V threshold.
Begin by selecting the total end-to-end resistance,
R
rent equivalent to a minimum 100 x I
bias current) at the desired overvoltage threshold.
For example, with an overvoltage threshold set to 1.8V:
R
input bias current.
High-Voltage, Overvoltage/Undervoltage,
Protection Switch Controller
6
TOTAL
TOTAL
_______________________________________________________________________________________
DC-DC Output Overvoltage Protection
IN
= R1 + R2. Choose R
< 1.8V/(100 x I
Setting Output Overvoltage Threshold (SET)
≥ 14V) with a 100µA pullup current. An over-
R
TOTAL
SET
), where I
< 360kΩ
TOTAL
Shutdown Control
to yield a total cur-
SET
GATE Voltage
IN
SET
exceeding the
is SET’s 50nA
(SET’s input
Use the following formula to calculate R2:
where V
overvoltage condition at the output of a DC-DC converter,
R2 = 100kΩ, R
Use a 261kΩ standard resistor.
Using a lower value for total resistance dissipates more
power but provides slightly better accuracy.
Figure 2. GATE Timing Diagram
Figure 3. Output Overvoltage Protection Configuration
V
IN
TH
IN
3V
is the 0.5V SET rising threshold and V
V
V
OV
IN
= 14V
= 4V
MAX6399
TOTAL
R
GATE
2 =
400ns/div
= R2 + R1, where R1 = 260kΩ.
V
GND
TH
OUT
SET
4V
×
R
TOTAL
V
IN
OV
CONVERTER
DC-DC
GND
V
500mV/div
V
10V/div
V
10V/div
OUT
DC_DC
GATE
OUT
V
OUT
OV
= 1.8V
R1
R2
is the