MAX17000A(2008_10) 查看數據表（PDF） - Maxim Integrated

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MAX17000A
(Rev.:2008_10)

Complete DDR2 and DDR3 Memory Power-Management Solution

Maxim Integrated 

Complete DDR2 and DDR3 Memory

Power-Management Solution

ΔI = VIN - VOUT

Δt

L

IPEAK

ILOAD = IPEAK/2

0

ON-TIME

TIME

Figure 3. Pulse-Skipping/Discontinuous Crossover Point

Forced-PWM Mode (SKIP = VCC)

The low-noise forced-PWM mode (SKIP = VCC) disables

the zero-crossing comparator, which controls the low-

side switch on-time. This forces the low-side gate-drive

waveform to constantly be the complement of the high-

side gate-drive waveform, so the inductor current

reverses at light loads while DH maintains a duty factor

of VOUT/VIN. The benefit of forced-PWM mode is to keep

a fairly constant switching frequency. However, forced-

PWM operation comes at a cost: the no-load 5V bias

current remains between 2mA to 20mA, depending on

the switching frequency.

STDBY = AGND overrides the SKIP pin setting, forcing

the MAX17000A into standby.

The MAX17000A switches to forced-PWM mode during

shutdown, regardless of the state of SKIP and STDBY

levels.

Standby Mode (STDBY)

It should be noted that standby mode in the

MAX17000A corresponds to computer system standby

operation, and is not referring to the MAX17000A shut-

down status.

When standby mode is enabled (STDBY = AGND),

VTT is disabled (high impedance) but VTTR remains

active.

When standby mode is disabled (STDBY = VCC), the

VTT block is enabled and the VTT output capacitor is

charged. The VTT soft-start current limit increases lin-

early from zero to its maximum current limit in 160μs

(typ), keeping the input VTTI inrush low. See Figure 4.

STDBY

SMPS OUTPUT

VTTR OUTPUT

VTT OUTPUT

VTT CURRENT LIMIT

PGOOD1

PGOOD2

STANDBY TIMING

Figure 4. MAX17000A Standby Mode Timing

VTT HIGH-IMPEDANCE

160μs

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