MAX8743(2004) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX8743
(Rev.:2004)

Dual, High-Efficiency, Step-Down Controller with High Impedance in Shutdown

Maxim Integrated 

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

Table 1. Component Selection for

Standard Applications

COMPONENT

Input Range

Q1 High-Side MOSFET

Q2 Low-Side MOSFET

Q3, Q4 High/Low-Side

MOSFETs

D1, D2 Rectifier

D3 Rectifier

SIDE 1: 1.8V AT 8A/

SIDE 2: 2.5V AT 4A

4.5V to 28V

Fairchild Semiconductor

FDS6612A

Fairchild Semiconductor

FDS6670A

Fairchild Semiconductor

FDS6982A

Nihon EP10QY03

Central Semiconductor

CMPSH-3A

L1 Inductor

2.2µH

Panasonic ETQP6F2R2SFA

or

Sumida CDRH127-2R4

L2 Inductor

4.7µH

Sumida CDRH124-4R7MC

C1 (3), C2 (2) Input

Capacitor

10µF, 25V

Taiyo Yuden

TMK432BJ106KM or

TDK C4532X5R1E106M

C3 (3), C4 Output Capacitor

470µF, 6V

Kemet T510X477M006AS or

Sanyo 6TPB330M

RSENSE1

5mΩ, ±1%, 1W

IRC LR2512-01-R005-F or

Dale WSL-2512-R005F

RSENSE2

10mΩ, ±1%, 0.5W

IRC LR2010-01-R010-F or

Dale WSL-2010-R010F

loops (including inductor and PC board resistance) and

the dead-time effect. These effects are the largest con-

tributors to the change of frequency with changing load

current. The dead-time effect increases the effective

on-time, reducing the switching frequency as one or

both dead times. It occurs only in PWM mode (SKIP =

high) when the inductor current reverses at light or neg-

ative load currents. With reversed inductor current, the

inductor’s EMF causes LX to go high earlier than nor-

mal, extending the on-time by a period equal to the

low-to-high dead time.

Table 2. Component Suppliers

MANUFACTURER

Central Semiconductor

Fairchild Semiconductor

International Rectifier

IRC

Kemet

NIEC (Nihon)

Panasonic

Sanyo

Sumida

Taiyo Yuden

TDK

Vishay/Dale

WEBSITE

www.centralsemi.com

www.fairchildsemi.com

www.irf.com

www.irctt.com

www.kemet.com

www.niec.co.jp

www.panasonic.com

www.sanyo.com/components

www.sumida.com

www.t-yuden.com

www.component.tdk.com

www.vishay.com

For loads above the critical conduction point, the actual

switching frequency is:

f = VOUT + VDROP1

tON(VIN + VDROP2)

where VDROP1 is the sum of the parasitic voltage drops

in the inductor discharge path, including synchronous

rectifier, inductor, and PC board resistances; VDROP2 is

the sum of the resistances in the charging path; and

tON is the on-time calculated by the MAX8743.

Automatic Pulse-Skipping Switchover

In skip mode (SKIP = GND), an inherent automatic

switchover to pulse-frequency modulation (PFM) takes

place at light loads. This switchover is effected by a

comparator that truncates the low-side switch on-time at

the inductor current’s zero crossing. This mechanism

causes the threshold between pulse-skipping PFM and

nonskipping PWM operation to coincide with the bound-

ary between continuous and discontinuous inductor-cur-

rent operation (also known as the critical conduction

point). For a 7V to 24V battery range, this threshold is rel-

atively constant, with only a minor dependence on bat-

tery voltage:

I LOAD(SKIP)

≈

K × VOUT_

2L

 VIN - VOUT_ 

 VIN 

where K is the on-time scale factor (Table 4). 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).

12 ______________________________________________________________________________________

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