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Chip information, Table 1. partial listing of capacitor vendors, Layout considerations – Rainbow Electronics MAX1673 User Manual

Page 8

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MAX1673

Regulated, 125mA-Output,
Charge-Pump DC-DC Inverter

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

8

_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 1998 Maxim Integrated Products

Printed USA

is a registered trademark of Maxim Integrated Products.

The expression for the ripple component predominantly
due to charge transfer is:

where C

FLY

and C

OUT

are their respective capacitance

values, ESR

COUT

is the equivalent series resistance of

C

OUT

, R

OUT

is the MAX1673 open-loop output imped-

ance (typically 3.5

, and f

OSC

is the MAX1673 switch-

ing frequency (typically 350kHz). If ESR

COUT

is very

small, as is likely when ceramic capacitors are used,
V

RIPPLE (TRANSFER)

dominates. If ESR is relatively

large, as with low-cost tantalum capacitors, then V

RIP-

PLE (ESR)

dominates.

When operating in LIN mode, use the following equa-
tion to approximate peak-to-peak output voltage ripple:

where C

OUT

is the output capacitor value, ESR

COUT

is

the output capacitor’s ESR, and f

OSC

is the MAX1673

oscillator frequency (typically 350kHz).

To ensure LIN mode stability over the entire tempera-
ture range, choose a low-ESR (no more than 100m

)

output capacitance using the following equation:

where C

OUT

is the output capacitor value, and f

MIN

is

the minimum oscillator frequency (250kHz). See Table
1 for a list of suggested capacitor suppliers.

Layout Considerations

The MAX1673’s high oscillator frequency requires good
layout technique, which ensures stability and helps
maintain the output voltage under heavy loads. Take
the following steps to ensure good layout:

• Mount all components as close together as possible.
• Place the feedback resistors R1 and R2 close to the

FB pin, and minimize the PC trace length at the FB
circuit node.

• Keep traces short to minimize parasitic inductance

and capacitance.

• Use a ground plane.

COUT = 75 x 10

- 6

R1

R1 + R2

OUT





I

V

=

I

2 f

C

2I

ESR

RIPPLE

OUT

OSC

OUT

OUT

COUT

+

V

f

R

(C

C

)

RIPPLE(ESR)

= 2

V

IN

– V

OUT

OSC

1

OUT

FLY

OUT









+

V

8

f

R

C

RIPPLE(ESR)

=

V

IN

– V

OUT

OSC

ESR

COUT

2

OUT FLY









PRODUCTION METHOD

MANUFACTURER

SERIES

PHONE

FAX

Surface-Mount Tantalum

AVX

TPS

(803) 946-0690

(803) 448-2170

Matsuo

267

(714) 969-2491

(714) 960-6492

Sprague

593D, 595D

(603) 224-1961

(603) 224-1430

Surface-Mount Ceramic

AVX

X7R

(803) 946-0590

(803) 626-3123

Matsuo

X7R

(714) 969-2491

(714) 960-6492

Table 1. Partial Listing of Capacitor Vendors

___________________Chip Information

TRANSISTOR COUNT: 386

SUBSTRATE CONNECTED TO: IN