MAX17021 datasheet(39/48 Pages) MAXIM

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Shutdown

When

SHDN goes low, the MAX17021/MAX17082/

MAX17482 enter low-power shutdown mode. PWRGD

is pulled low immediately, and the output voltage ramps

down at 1/8 the slew rate set by RTIME:

where dVTARGET/dt = 12.5mV/μs x 71.5kΩ/RTIME is the

slew rate. Slowly discharging the output capacitors by

slewing the output over a long period of time keeps the

average negative inductor current low (damped

response), thereby eliminating the negative output-volt-

age excursion that occurs when the controller dis-

charges the output quickly by permanently turning on

the low-side MOSFET (underdamped response). This

eliminates the need for the Schottky diode normally

connected between the output and ground to clamp

the negative output-voltage excursion. After the con-

troller reaches the zero target, the MAX17021/

MAX17082/MAX17482 shut down completely—the dri-

vers are disabled (DL1 and DL2 driven low) and the

supply current drops below 1μA.

When a fault condition—output UVLO or thermal shut-

down—activates the shutdown sequence, the protection

circuitry sets the fault latch to prevent the controller from

restarting. To clear the fault latch and reactivate the con-

troller, toggle

SHDN or cycle VCC power below 0.5V.

Current Monitor (IMON)

(MAX17021/MAX17482 Only)

The MAX17082/MAX17482 includes a unidirectional

transconductance amplifier that sources current pro-

portional to the positive current-sense voltage. The

IMON output current is defined by:

IIMON = Gm(IMON) x

Σ(VCSP_ - VCSN_)

where Gm(IMON) = 2.4mS (typ) and the IMON current is

unidirectional (sources current out of IMON only) for

positive current-sense values. For negative current-

sense voltages, the IMON current is zero.

The current monitor allows the processor to accurately

monitor the CPU load and quickly calculate the power

dissipation to determine if the system is about to over-

heat before the significantly slower temperature sensor

signals an over-temperature alert.

Connect an external resistor between IMON and

VSS_SENSE to create the desired IMON gain based on

the following equation:

RIMON = 0.999V/(IMAX x RSENSE x Gm(IMON))

where IMAX is defined in the

Current Monitor section of

the Intel IMVP-6.5 specification and based on discrete

increments (10A, 20A, 30A, 40A, etc.), RSENSE is the

typical effective value of the current-sense element

(sense resistor or inductor DCR) that is used to provide

the current-sense voltage, and Gm(IMON) is the typical

transconductance amplifier gain as defined in the

Electrical Characteristics table.

The IMON voltage is internally clamped to a maximum

of 1.1V (typ), preventing the IMON output from exceed-

ing the IMON voltage rating even under overload or

short-circuit conditions. When the controller is disabled,

IMON is pulled to ground.

To filter the IMON signal, use an RC filter as shown in

Figure 2. The filter time constant is (R7 + R8) x C15.

Phase Fault (PHASEGD)

The MAX17021/MAX17082/MAX17482 include a phase-

fault output that signals the system that one of the two

phases either has a fault condition or is not matched with

the other. Detection is done by identifying the need for a

large on-time difference between phases in order to

achieve or move towards current balance.

PHASEGD is high impedance when the controller oper-

ates in one-phase mode (DPRSLPVR high or

PSI low

and DPRSLPVR low). On exit to two-phase mode,

PHASEGD is forced high impedance for 32 switching

cycles on DH2.

PHASEGD is low in shutdown. PHASEGD is forced high

impedance whenever the slew-rate controller is active

(output-voltage transitions).

Temperature Comparator (VRHOT)

The MAX17021/MAX17082/MAX17482 also feature an

independent comparator with an accurate threshold

(VHOT) that tracks the analog supply voltage (VHOT =

0.3VCC). This makes the thermal trip threshold indepen-

dent of the VCC supply voltage tolerance. Use a resis-

tor- and thermistor-divider between VCC and GND to

generate a voltage-regulator over-temperature monitor.

Place the thermistor as close to the MOSFETs and

inductors as possible.

Fault Protection (Latched)

Output Overvoltage Protection

(MAX17021/MAX17082 Only)

The overvoltage-protection (OVP) circuit is designed to

protect the CPU against a shorted high-side MOSFET

by drawing high current and blowing the battery fuse.

The MAX17021/MAX17082 continuously monitor the

output for an overvoltage fault. The controller detects

an OVP fault if the output voltage exceeds the set VID

DAC voltage by more than 300mV, regardless of the

operating state. During downward transitions in

TRAN SHDN

OUT

TARGET

() =

()

Dual-Phase, Quick-PWM Controllers for

IMVP-6+/IMVP-6.5 CPU Core Power Supplies

______________________________________________________________________________________

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