5

 2005 Semtech Corp.

www.semtech.com

SC613

POWER MANAGEMENT

Block Diagram

Applications Information

Charge Pump Doubler Type

The SC613 uses a voltage doubler circuit which is implemented

with two switched or ‘bucket’ capactors. Most charge pump dou-

blers use only one bucket capacitor. Two bucket capacitors switch-

ing on alternate phases greatly reduce the output ripple voltage

and also reduce the size requirement for the output capacitor.

Over Voltage Protection

The output is prevented from exceeding 6.0V. This feature allows

the use of 6.3V ceramic capacitors.

Comparison with Other Regulation Methods

In many instances, a charge pump regulator is the best choice for

portable power applications. These regulators offer many advan-

tages over switch mode regulators. A smaller bill of materials,

less layout area, lower component height, less noise, no EMF, and

less overall circuit cost are typical reasons to use this type of

regulation. The efficiency of a charge pump regulator often ap-

proaches and in some cases exceeds the efficiency of a switch

mode regulator.

Inductors are often the largest and most expensive discrete com-

ponent in a design. There are no inductors used in the SC613, so

the inductor’s cost and layout area are eliminated. The noise and

EMF associated with the inductor are also eliminated.

The SC613’s fixed frequency harmonics are an advantage in por-

table communications equipment, such as cellular telephones.

The SC613 has distinct frequencies of operation, so the harmon-

ics are predictable. The harmonics are not fixed in a switch mode

regulator. Switch mode regulators have harmonics which vary

due to the pulse width modulation used to regulate the output.

Varying harmonics can be a problem because it may be more

EN

FSEL

VSEL

GND

VIN

6

5

4

8

3

MODE

SELECT

DRIVERS

SWITCH

BLOCK

TIMER

COMPARATORS

VIN

VOUT

VREF

VIN

CF1+

CF1-

CF2+

CF2-

VOUT

2

9

10

7

1

EN

OSC

650kHz or 262kHz

5.0V or 4.5V

4

5

difficult to ensure acceptable noise performance over the entire

operating range.

Many switch mode regulators have increased voltage ripple on

the output during pulse skipping mode due to the fact that there

are large periods of time when no current is supplied to the output.

The SC613 supplies current to the output continuously, so the

voltage ripple is less than a switch mode regulator, even with greatly

reduced output capacitance.

Frequency Selection

The FSEL input is for frequency selection. A logic High level at this

input will set the clock frequency to 650kHz, while a logic Low sets

the clock to 262kHz. Input from a uP or other device may be used

to change the charge pump frequency at any time. The optimal

frequency will depend upon the capacitor values, the load current,

and the exceptable amount of output ripple.

Ripple Performance

Examples of the output ripple per charge pump frequency and

output voltage are listed in the Ripple Performance table on page

5.

Efficiency

Efficiency for the SC613 is defined as,

=

where V

I

O

= output current

V

I

on page 2].

η

⋅

⋅

+

()

⋅