MAX1717 查看數據表（PDF） - Maxim Integrated

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MAX1717

Dynamically Adjustable, Synchronous Step-Down Controller for Notebook CPUs

Maxim Integrated 

Dynamically Adjustable, Synchronous

Step-Down Controller for Notebook CPUs

VBATT

+5V

BIAS SUPPLY

C5

R1

1μF

20Ω

C6

1μF

C1

TO VCC

ON/OFF

CONTROL

R7

120kΩ

7

VCC

1

V+

2 SKP/SDN

3

TIME

15

VDD

22

BST

DH 24

100kΩ

21

D0

20 D1

19 D2

18 D3

17 D4

MAX1717 LX 23

DL 14

GND 13

D2

CMPSH-3

C7

0.1μF

Q1 L1

1μH

Q2 D1

R6

0.005Ω

C2

HIGH/LOW

C4

1μF

8

TON

9 REF

6 CC

C3

470pF

16

A/B

FB

FBS

GNDS

4

5

11

+5V

12

ILIM VGATE

10

TO VCC

R2

100kΩ

POWER-GOOD

INDICATOR

R4

2kΩ

R5

150kΩ

TO VREF

D1 = INTL RECT 10MQ040N.

FOR OTHER COMPONENTS,

SEE TABLE 1 VALUES.

Figure 3. Voltage-Positioned Circuit

VOUT

A/B = LOW = 1.60V

A/B = HIGH = 1.35V

For a battery range of 7V to 24V, this threshold is rela-

tively constant, with only a minor dependence on bat-

tery voltage:

I LOAD(SKIP) ≈

K × VOUT

2×L

× VBATT − VOUT

VBATT

where K is the on-time scale factor (Table 3). The load-

current level at which PFM/PWM crossover occurs,

ILOAD(SKIP), is equal to 1/2 the peak-to-peak ripple cur-

rent, which is a function of the inductor value (Figure 4).

For example, in the standard application circuit this

becomes:

3.3μs × 1.6V × 12V − 1.6V = 2.3A

2 × 1μH

12V

The crossover point occurs at an even lower value if a

swinging (soft-saturation) inductor is used.

The switching waveforms may appear noisy and asyn-

chronous when light loading causes pulse-skipping

operation, but this is a normal operating condition that

results in high light-load efficiency. Trade-offs in PFM

noise vs. light-load efficiency are made by varying the

inductor value. Generally, low inductor values produce

a broader efficiency vs. load curve, while higher values

result in higher full-load efficiency (assuming that the

coil resistance remains fixed) and less output voltage

ripple. Penalties for using higher inductor values

include larger physical size and degraded load-tran-

sient response (especially at low input voltage levels).

______________________________________________________________________________________ 17

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