MAX6399 查看數據表（PDF） - Maxim Integrated

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MAX6399

High-Voltage, Overvoltage/Undervoltage, Protection Switch Controller

Maxim Integrated 

High-Voltage, Overvoltage/Undervoltage,

Protection Switch Controller

The MAX6399 includes internal thermal-shutdown pro-

tection, disabling the external MOSFET if the device

reaches overtemperature conditions.

Shutdown Control

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.

GATE Voltage

The MAX6399 uses a high-efficiency charge pump to

generate the GATE voltage. Upon VIN exceeding the

5V (typ) UVLO threshold, GATE enhances 10V above

IN (for VIN ≥ 14V) with a 100µA pullup current. An over-

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.

DC-DC Output Overvoltage Protection

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.

Setting Output Overvoltage Threshold (SET)

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,

RTOTAL = R1 + R2. Choose RTOTAL to yield a total cur-

rent equivalent to a minimum 100 x ISET (SET’s input

bias current) at the desired overvoltage threshold.

For example, with an overvoltage threshold set to 1.8V:

RTOTAL < 1.8V/(100 x ISET), where ISET is SET’s 50nA

input bias current.

RTOTAL < 360kΩ

VOV = 4V

4V

VIN = 14V

3V

VDC_DC

500mV/div

VGATE

10V/div

400ns/div

Figure 2. GATE Timing Diagram

VOUT

10V/div

VIN

IN

GATE

OUT

MAX6399 SET

GND

DC-DC

CONVERTER VOUT = 1.8V

IN

OUT

GND

R1

R2

Figure 3. Output Overvoltage Protection Configuration

Use the following formula to calculate R2:

R2 = VTH × RTOTAL

VOV

where VTH is the 0.5V SET rising threshold and VOV is the

overvoltage condition at the output of a DC-DC converter,

R2 = 100kΩ, RTOTAL = R2 + R1, where R1 = 260kΩ.

Use a 261kΩ standard resistor.

Using a lower value for total resistance dissipates more

power but provides slightly better accuracy.

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