Low-Cost, Dual-Output, Step-Down

Controller with Fast Transient Response

10

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The threshold that trips overcurrent protection is set by a

resistor connected from ILIM_ to the drain of the high-

side MOSFET(s). ILIM_ sinks 50µA (typ) through this

resistor. When the drain-source voltage exceeds the volt-

age drop across this resistor during the high-side

MOSFET(s) on-time, an overcurrent fault is triggered. To

prevent glitches from falsely tripping the overcurrent pro-

tection, connect a filter capacitor (0.01µF typically) in

parallel with the overcurrent-setting resistor.

Output Overvoltage Protection (OVP)

During an overvoltage event on one or both of its out-

puts, the MAX8664 latches off the controller. This

occurs when the feedback voltage exceeds its normal

regulation voltage by 150mV for 10µs. In this state, the

low-side MOSFET(s) are on and the high-side MOS-

FET(s) are off to discharge the output. To clear the

latch, cycle EN or the input power.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX8664. When the junction temperature

exceeds +160°C, an internal thermal sensor shuts down

the device, pulling DH_ and DL_ low for both controllers.

To restart the controller, cycle EN or input power.

Power-Good Output (PWRGD)

PWRGD is an open-drain output that is pulled low when

the output voltage rises above the PWRGD upper

threshold or falls below the PWRGD falling threshold.

UVLO threshold, during soft-start, and during fault con-

ditions. PWRGD does not reflect the status of controller

2 in the MAX8664A, or when REFIN2 is connected to an

external reference with either version. See Table 1 for

PWRGD operation of the circuits of Figures 2–5 during

fault conditions. For logic-level output voltages, con-

nect an external pullup resistor between PWRGD and

the logic power supply. A 100kΩ resistor works well in

most applications.

Fault-Shutdown Modes

When an overvoltage or overcurrent fault occurs on one

controller of the MAX8664A, the second controller con-

tinues to operate. With the MAX8664B, a fault in one

controller latches off both controllers automatically, and

PWRGD is pulled low. See Table 1 for the fault-shut-

down modes of the circuits shown in Figures 2–5.

Table 1. Fault Shutdown Modes for Circuits of Figures 2–5

MAX8664A (INDEPENDENT)

MAX8664B (JOINT)

CIRCUIT

CONTROLLER 1 FAULT

CONTROLLER 2 FAULT

CONTROLLER 1 FAULT

CONTROLLER 2 FAULT

Figure 2,

Figure 5

(Independent)

Controller 2 remains on.

PWRGD is pulled low.

Controller 1 remains on.

PWRGD remains high.

Controller 2 is shut down.

PWRGD is pulled low.

Controller 1 is shut down.

PWRGD is pulled low.

Figure 3

(Tracking)

Controller 2 shuts down.

PWRGD is pulled low.

Controller 1 remains on.

PWRGD remains high.

Controller 2 is shut down.

PWRGD is pulled low.

Controller 1 is shut down.

PWRGD is pulled low.

Figure 4

(Sequenced)

Controller 2 shuts down.

PWRGD is pulled low.

Controller 1 remains on.

PWRGD remains high.

Controller 2 is shut down.

PWRGD is pulled low.

Controller 1 is shut down.

PWRGD is pulled low.