MAX1715EEI+T Datasheet MAX1715EEI+, MAX1715EEI+T | P10-P12

MAX1715

Ultra-High Efficiency, Dual Step-Down

Controller for Notebook Computers

10 ______________________________________________________________________________________

= 5V

BIAS SUPPLY

PINS 15, 23, 28 = N.C.

POWER-GOOD

INDICATOR

MAX1715

OUTPUT1

1.8V

4.5V TO 28V

CMPSH-3A

ILIM1

ON1

DL1

TON

OUT1

AGND

C3 C4

LX1

DH1

0.1μF

0.22μF

FB1

1μF

C11

1μF

BST1

ILIM2

REF

ON1

ON2

DL2

PGND

+5V

100k

OUT2

LX2

DH2

FB2

PGOOD

V+

BST2

SKIP

4.7μF

20Ω

OUTPUT2

2.5V

ON/OFF

CONTROLS

Figure 1. Standard Application Circuit

Standard Application Circuit

The standard application circuit (Figure 1) generates

two low-voltage rails for general-purpose use in note-

book computers (I/O supply, fixed CPU core supply,

DRAM supply). This DC-DC converter steps down a

battery or AC adapter voltage to voltages from 1.0V to

5.5V with high efficiency and accuracy.

See Table 1 for a list of components for common appli-

cations. Table 2 lists component manufacturers.

Detailed Description

The MAX1715 buck controller is designed for low-volt-

age power supplies for notebook computers. Maxim’s

proprietary Quick-PWM pulse-width modulator in the

MAX1715 (Figure 2) is specifically designed for han-

dling fast load steps while maintaining a relatively con-

stant operating frequency and inductor operating point

over a wide range of input voltages. The Quick-PWM

architecture circumvents the poor load-transient timing

problems of fixed-frequency current-mode PWMs while

also avoiding the problems caused by widely varying

switching frequencies in conventional constant-on-time

and constant-off-time PWM schemes.

+5V Bias Supply (V

and V

)

The MAX1715 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.

MAX1715

Ultra-High Efficiency, Dual Step-Down

Controller for Notebook Computers

______________________________________________________________________________________ 11

The power input and +5V bias inputs can be connected

together if the input source is a fixed +4.5V to +5.5V

supply. If the +5V bias supply is powered up prior to

the battery supply, the enable signal (ON1, ON2) must

be delayed until the battery voltage is present to ensure

start-up. The +5V bias supply must provide V

and

gate-drive power, so the maximum current drawn is:

BIAS

= I

+ f (QG1 + QG2) = 5mA to 30mA (typ)

where ICC is 1mA typical, f is the switching frequency,

and QG1 and QG2 are the MOSFET data sheet total

gate-charge specification limits at V

= 5V.

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 type with

voltage feed-forward (Figure 3). This architecture relies

on the output filter capacitor’s ESR to act as the cur-

rent-sense resistor, so the output ripple voltage pro-

vides the PWM ramp signal. The control algorithm is

simple: the high-side switch on-time is determined sole-

ly by a one-shot whose period is inversely proportional

to input voltage and directly proportional to output volt-

age. Another one-shot sets a minimum off-time (400ns

typ). The on-time one-shot is triggered if the error com-

parator is low, the low-side switch current is below the

Table 1. Component Selection for Standard Applications

Table 2. Component Suppliers

4.75V to 5.5V7V to 20V7V to 20VInput Range

100µF, 10V

Sanyo POSCAP

10TPA100M

470µF, 4V Sanyo

POSCAP 4TPB470M

470µF, 4V Sanyo

POSCAP 4TPB470M

C2 Output Capacitor

100µF, 10V

Sanyo POSCAP

10TPA100M

10µF, 25V

Taiyo Yuden

TMK432BJ106KM

10µF, 25V

Taiyo Yuden

TMK432BJ106KM

C1 Input Capacitor

3.3µH

TOKO D73LC

3.1µH

Sumida CDRH125

4.4µH

Sumida CDRH125

L1 Inductor

—Nihon EP10QY03Nihon EP10QY03D2 Rectifier

International Rectifier

1/2 IRF7301

Fairchild

Semiconductor

1/2 FDS6982A

Fairchild

Semiconductor

1/2 FDS6982A

Q2 Low-Side MOSFET

International Rectifier

1/2 IRF7301

Fairchild

Semiconductor

1/2 FDS6982A

Fairchild

Semiconductor

1/2 FDS6982A

Q1 High-Side MOSFET

600kHz345kHz255kHz

Frequency

3.3V at 1.5A1.8V at 4A2.5V at 4ACOMPONENT

[1] 602-994-6430602-303-5454Motorola

[1] 408-986-1442408-986-0424Kemet

[1] 408-721-1635408-822-2181Fairchild Semiconductor

[1] 561-241-9339561-241-7876Coiltronics

[1] 847-639-1469847-639-6400Coilcraft

[1] 516-435-1824516-435-1110Central Semiconductor

[1] 803-626-3123803-946-0690AVX

FACTORY FAX

[Country Code]

USA PHONEMANUFACTURER

[1] 714-960-6492714-969-2491Matsuo

[1] 310-322-3332310-322-3331International Rectifier

[1] 408-573-4159408-573-4150Taiyo Yuden

[1] 603-224-1430603-224-1961Sprague

[1] 408-970-3950

408-988-8000

800-554-5565

Siliconix

[81] 7-2070-1174619-661-6835Sanyo

[81] 3-3494-7414805-867-2555*NIEC (Nihon)

[1] 814-238-0490

814-237-1431

800-831-9172

Murata

[81] 3-3607-5144847-956-0666Sumida

[1] 847-390-4405847-390-4461TDK

*Distributor

7V to 20V

(2) 470µF, 6V Kemet

T510X477108M0

06AS

(2) 10µF, 25V

Taiyo Yuden

TMK432BJ106KM

1.5µH Sumida

CEP125-1R5MC

Motorola

MBRS340T3

Fairchild

Semiconductor

FDS6670A

International

Rectifier IRF7811

255kHz

1.3V at 8A

7V to 20V

330µF, 6V AVX

TPSV337M006R

0060

10µF, 25V

Taiyo Yuden

TMK432BJ106KM

6.8µH

Coiltronics UP2B

Nihon EP10QY03

Fairchild

Semiconductor

1/2 FDS6990A

Fairchild

Semiconductor

1/2 FDS6990A

255kHz

5V at 3A

[1] 708-699-1194800-PIK-TOKOTOKO

MAX1715

Ultra-High Efficiency, Dual Step-Down

Controller for Notebook Computers

12 ______________________________________________________________________________________

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

shot has timed out.

On-Time One-Shot (TON)

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

high-side switch on-time for both controllers. This fast,

low-jitter, adjustable one-shot includes circuitry that

varies the on-time in response to battery and output

voltage. The high-side switch on-time is inversely pro-

portional to the battery voltage as measured by the V+

input, and proportional to the output voltage. This algo-

rithm results in a nearly constant switching frequency

despite the lack of a fixed-frequency clock generator.

The benefits of a constant switching frequency are

twofold: first, the frequency can be selected to avoid

noise-sensitive regions such as the 455kHz IF band;

second, the inductor ripple-current operating point

remains relatively constant, resulting in easy design

methodology and predictable output voltage ripple.

The on-times for side 1 are set 15% higher than the

REF

AGND

REF

OUT2

FB2

20Ω

PGND

OUTPUT2

2.5V

DL2

LX2

ZERO

CROSSING

CURRENT

LIMIT

PWM

CONTROLLER

(SEE FIGURE 3)

DH2

BST2

LIM_

V+

OUT1

FB1

SKIP

TON

ON1

ON2

OUTPUT1

1.8V

5V INPUT

DL1

LX1

ZERO

CROSSING

CURRENT

LIMIT

DH1

LIM_

BATTERY

4.5V TO 28V

5μA

BST1

V+

PWM

CONTROLLER

(SEE FIGURE 3)

MAX1715

5μA

GOOD

Figure 2. Functional Diagram

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P25

MAX1715EEI+T

Mfr. #:

Buy MAX1715EEI+T

Manufacturer:

Maxim Integrated

Description:

Switching Controllers Dual Step-Down Controller

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MAX1715EEI+T

MAX1715EEI+T

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