MAX17000 查看數據表（PDF） - Maxim Integrated

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MAX17000

Complete DDR2 and DDR3 Memory Power-Management Solution

Maxim Integrated 

MAX17000

Complete DDR2 and DDR3 Memory

Power-Management Solution

+5V Bias Supply (VDD, VCC)

The MAX17000 requires an external 5V bias supply in

addition to the battery. Typically, this 5V bias supply is

the notebook’s 95% efficient 5V system supply.

Keeping the bias supply external to the IC improves

efficiency and eliminates the cost associated with the

5V linear regulator that would otherwise be needed to

supply the PWM circuit and gate drivers. If stand-alone

capability is needed, the 5V supply can be generated

with an external linear regulator such as the MAX1615.

The 5V bias supply powers both the PWM controller

and internal gate-drive power, so the maximum current

drawn is:

IBIAS = IQ + fSWQG(MOSFETs) = 2mA to 20mA (typ)

where IQ is the current for the PWM control circuit, fSW

is the switching frequency, and QG(MOSFETs) is the

total gate-charge specification limits at VGS = 5V for the

internal MOSFETs.

Free-Running Constant-On-Time PWM

Controller with Input Feed-Forward

The Quick-PWM control architecture is a pseudo-fixed-

frequency, constant on-time, current-mode regulator

with voltage feed-forward. This architecture utilizes the

output filter capacitor’s ESR to act as a current-sense

resistor, so the output ripple voltage can provide the

PWM ramp signal. In addition to the general Quick-

PWM, the MAX17000 also senses the inductor current

through DCR method or with a sensing resistor.

Therefore, it is less dependent on the output capacitor

ESR for stability. The control algorithm is simple: the

high-side switch on-time is determined solely by a one-

shot whose pulse width is inversely proportional to input

voltage and directly proportional to output voltage.

Another one-shot sets a minimum off-time (250ns typ).

The on-time one-shot is triggered if the error compara-

tor is low, the low-side switch current is below the valley

current-limit threshold, and the minimum off-time one-

shot has timed out.

On-Time One-Shot

The heart of the PWM core is the one-shot that sets the

high-side switch on-time. This fast, low-jitter, adjustable

one-shot includes circuitry that varies the on-time in

response to battery and output voltages. The high-side

switch on-time is inversely proportional to the battery

voltage as measured by the VIN input, and proportional

to the output voltage.

An external resistor between the input power source

and TON pin sets the switching frequency per phase

according to the following equation:

tON

=

CTON

×

(RTON

+

6.5kΩ)

VIN

×

(VCSL

+

0.075V)

fSW

=

CTON

×

1

(RTON

+

6.5kΩ)

where CTON = 16.26pF, and 0.075V is an approxima-

tion to accommodate for the expected drop across the

low-side MOSFET switch. This algorithm results in a

nearly constant switching frequency despite the lack of

a fixed-frequency clock generator.

For loads above the critical conduction point, where the

dead-time effect is no longer a factor, the actual switch-

ing frequency is:

fSW

=

tON

×

VOUT

(VIN −

+ VDIS

VCHG +

VDIS )

where VDIS is the sum of the parasitic voltage drops in

the inductor discharge path, including synchronous

rectifier, inductor, and PCB resistances; VCHG is the

sum of the parasitic voltage drops in the charging path,

including the high-side switch, inductor, and PCB resis-

tances; and tON is the on-time calculated by the

MAX17000.

Automatic Pulse-Skipping Mode

(SKIP = AGND)

In skip mode (SKIP = AGND), an inherent automatic

switchover to PFM takes place at light loads. This

switchover is affected by a comparator that truncates

the low-side switch on-time at the inductor current’s

zero crossing.

DC output-accuracy specifications refer to the thresh-

old of the error comparator. When the inductor is in

continuous conduction, the MAX17000 regulates the

valley of the output ripple, so the actual DC output volt-

age is higher than the trip level by 50% of the output

ripple voltage. In discontinuous conduction (SKIP =

AGND and IOUT < ILOAD(SKIP)), the output voltage has

a DC regulation level higher than the error-comparator

threshold by approximately 1.5% due to slope compen-

sation. However, the internal integrator corrects for

most of it, resulting in very little load regulation.

STDBY = AGND overrides the SKIP pin setting, forcing

the MAX17000 into standby.

18

Maxim Integrated

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