MAX6397_ATA-T 查看數據表（PDF） - Maxim Integrated

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MAX6397_ATA-T

Overvoltage Protection Switch/Limiter Controllers Operate Up to 72V

Maxim Integrated 

Overvoltage Protection Switch/Limiter

Controllers Operate Up to 72V

IN

THERMAL

PROTECTION

5V

SET

1.23V

UVLO

LINEAR

REGULATOR

10V

CHARGE

PUMP

GATE

OUT

SHDN

REG

MAX6397

POK

MAX6398

VPOK_TH

GND

MAX6397 ONLY

Figure 1. Functional Diagram

The MAX6397 integrates a high-input-voltage, low-qui-

escent-current linear regulator in addition to an over-

voltage protector circuit. The linear regulator remains

enabled at all times to power low-current “always-on”

applications (independent of the state of the external

MOSFET). The regulator is offered with several stan-

dard output voltage options (5V, 3.3V, 2.5V, or 1.8V).

An open-drain power-good output notifies the system if

the regulator output falls to 92.5% or 87.5% of its nomi-

nal voltage. The MAX6397’s REG output operates inde-

pendently of the SHDN logic input.

The MAX6397/MAX6398 include internal thermal-shut-

down protection, disabling the external MOSFET and

linear regulator if the chip reaches overtemperature

conditions.

Linear Regulator (MAX6397 Only)

The MAX6397 is available with 5.0V, 3.3V, 2.5V, and 1.8V

factory-set output voltages. Each regulator sources up to

100mA and includes a current limit of 230mA. The linear

regulator operates in an always-on condition regardless

of the SHDN logic. For fully specified operation, VIN must

be greater than 6.5V for the MAX6397L/M (5V regulator

output). The actual output current may be limited by the

operating condition and package power dissipation.

Power-OK Output

POK is an open-drain output that goes low when REG

falls to 92.5% or 87.5% (see the Selector Guide) of its

nominal output voltage. To obtain a logic-level output,

connect a pullup resistor from POK to REG or another

system voltage. Use a resistor in the 100kΩ range to

minimize current consumption. POK provides a valid

logic-output level down to VIN = 1.5V.

GATE Voltage

The MAX6397/MAX6398 use a high-efficiency charge

pump to generate the GATE voltage. Upon VIN exceed-

ing the 5V (typ) UVLO threshold, GATE enhances 10V

above IN (for VIN ≥14V) with a 75µA pullup current. An

overvoltage condition occurs when the voltage at SET

pulls above its 1.215V threshold. When the threshold is

crossed, GATE falls to OUT within 100ns with a 100mA

(typ) pulldown current. The MAX6397/MAX6398 include

an internal clamp to OUT that ensures GATE is limited

to 18V (max) above OUT to prevent gate-to-source

damage to the external FET.

The GATE cycle during overvoltage limit and overvolt-

age switch modes are quite similar but have distinct

characteristics. In overvoltage switch mode (Figure 2a),

GATE is enhanced to VIN + 10V while the monitored IN

voltage remains below the overvoltage fault threshold

(SET < 1.215V). When an overvoltage fault occurs (SET

≥ 1.215V), GATE is pulled one diode below OUT, turn-

ing off the external FET and disconnecting the load

from the input. GATE remains low (FET off) as long as

VIN is above the overvoltage fault threshold. As VIN falls

back below the overvoltage fault threshold (-5% hys-

teresis) GATE is again enhanced to VIN + 10V.

In overvoltage limit mode (Figure 2b), GATE is enhanced

to VIN + 10V. While the monitored OUT voltage remains

below the overvoltage fault threshold (SET < 1.215V).

When an overvoltage fault occurs (SET ≥ 1.215V),

GATE is pulled low one diode drop below OUT until

OUT drops 5% below the overvoltage fault threshold.

GATE is then turned back on until OUT again reaches

the overvoltage fault threshold and GATE is again

turned off.

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