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

The MAX17000 always uses skip mode during startup,

regardless of the SKIP and STDBY setting. The SKIP

and STDBY controls take effect after soft-start is done.

See Figure 3.

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

ΔI

=

VIN - VOUT

Δt

L

IPEAK

ILOAD = IPEAK/2

0

ON-TIME

TIME

Figure 3. Pulse-Skipping/Discontinuous Crossover Point

current remains between 2mA to 20mA, depending on

the switching frequency.

STDBY = AGND overrides the SKIP pin setting, forcing

the MAX17000 into standby.

The MAX17000 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 MAX17000

corresponds to computer system standby operation,

and is not referring to the MAX17000 shutdown status.

When standby mode is enabled (STDBY = AGND), the

MAX17000 switches over from the fast internal PWM

block to a low-quiescent current mode using a low-

power valley comparator to initiate an on-time pulse.

The zero-crossing comparator is enabled so that the

MAX17000 only operates in discontinuous mode,

reducing the maximum available output current by 1/6.

The system is NOT expected to have any fast load tran-

sients in such a state. While in standby, VTT is disabled

(high impedance) but VTTR remains active. SKIP is

ignored when standby mode is enabled.

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

MAX17000 reenables its fast internal PWM block. Once

the internal SMPS block is ready, the VTT block is

enabled and the VTT output capacitor is charged. The

VTT soft-start current limit increases linearly from zero

to its maximum current limit in 160μs (typ), keeping the

input VTTI inrush low. See Figure 4.

STDBY

SMPS_RUNOK

SMPS OUTPUT

VTTR OUTPUT

VTT OUTPUT

VTT CURRENT LIMIT

PGOOD1

PGOOD2

< 50μs

VTT HIGH IMPEDANCE

160μs

Figure 4. MAX17000 Standby Mode Timing

Maxim Integrated

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