MAX1624-MAX1625 查看數據表（PDF） - Maxim Integrated

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MAX1624-MAX1625

High-Speed Step-Down Controllers with Synchronous Rectification for CPU Power

Maxim Integrated 

High-Speed Step-Down Controllers with

Synchronous Rectification for CPU Power

Table 4. Output Voltage-Adjustment

Settings

D4

D3

D2

D1 D0

OUTPUT

VOLTAGE (V)

COMPATIBILITY

10 0 00

3.5

10 0 01

3.4

10 0 10

3.3

10 0 11

3.2

10 1 00

3.1

10 1 01

3.0

10 1 10

2.9

10 1 11

2.8

11 0 00

2.7

11 0 01

2.6

11 0 10

2.5

11 0 11

2.4

11 1 00

2.3

11 1 01

2.2

11 1 10

2.1

1 1 1 1 1 No CPU (off)

00 0 00

1.9

00 0 01

1.8

00 0 10

1.7

00 0 11

1.6

00 1 00

1.5

00 1 01

1.4

00 1 10

1.3

00 1 11

1.2

01 0 00

1.1

01 0 01

1.1

0 1 — ——

1.1

01 1 10

1.1

0 1 1 1 1 No CPU (off)

Intel-compatible

DAC codes

Non-Intel-

compatible

DAC codes

MAX1625

Set the output voltage by connecting R2 and R3 (Fig-

ure 7) to the FB pin from the output to AGND. R2 is

given by the following equation:

R2

=

R3

x





VOUT

VFB

−



1 

where VFB = 1.1V. Since the input bias current at FB

has a maximum value of ±0.1µA, values up to 100kΩ

can be used for R3 with no significant accuracy loss.

Values under 1kΩ are recommended to improve noise

immunity and minimize parasitic capacitance at the FB

node. Place R2 and R3 very close to the MAX1625,

within 0.2 in. (5mm) of the FB pin.

Selecting the Oscillator Frequency

Set the switching frequency between 100kHz and

1MHz by connecting a resistor from FREQ to AGND.

Select the resistor according to the following equation:

R4 = 2 x 1010

fOSC

Low-frequency operation reduces controller IC quies-

cent current and improves efficiency. High-frequency

operation reduces cost and PC board area by allowing

the use of smaller inductors and fewer and smaller out-

put capacitors. Inductor energy-storage requirements

and output capacitor requirements at 1MHz are one-

third those at 300kHz.

Choosing the

Error-Amplifier Gain (MAX1624)

Set the error-amplifier gain to match the voltage-preci-

sion requirements of the CPU used. The MAX1624’s

loop-gain control input (LG) allows trade-offs in DC/AC

voltage accuracy versus output filter capacitor require-

ments. AC load regulation can be set to 0.5%, 1%,

or 2% by connecting LG as shown in Table 5. The

MAX1625’s default AC regulation is 1%.

DC load regulation is typically 10 times better than AC

load regulation, and is determined by the gain set by

the LG pin.

Table 5. LG Pin Adjustment Settings

LG

CONNECTED

TO

AC LOAD-

REGULATION

ERROR

(%)

DC LOAD-

REGULATION

ERROR

(%)

VCC

2

0.2

REF

1

0.1

GND

0.5

0.05

TYPICAL

AE

(VGAIN/

IGAIN)

2

4

8

Specifying the Inductor

Three key inductor parameters must be specified:

inductance value (L), peak current (IPEAK), and DC

resistance (RDC). The following equation includes a

constant LIR, which is the ratio of inductor peak-to-

peak AC current to DC load current. A higher LIR

value allows for smaller inductors and better transient

response, but results in higher losses and output ripple.

______________________________________________________________________________________ 17

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