MAX865 Ver la hoja de datos (PDF) - Maxim Integrated

Número de pieza

componentes Descripción

Fabricante

MAX865

Compact, Dual-Output Charge Pump

Maxim Integrated 

Compact, Dual-Output Charge Pump

converter (RS+), where ILOAD+ is the combination of IV-

and the external load on V+ (IV+):

( ) VDROOP+ = ILOAD+ x RS+ = IV+ + IV- x RS+

Determine V+ and V- as follows:

V+ = 2VIN - VDROOP+

V - = (V+ - VDROOP ) = -(2VIN - VDROOP+ - VDROOP- )

The output resistance for the positive and negative

charge pumps are tested and specified separately. The

positive charge pump is tested with V- unloaded. The

negative charge pump is tested with V+ supplied from

an external source, isolating the negative charge

pump.

Current draw from either V+ or V- is supplied by the

reservoir capacitor alone during one half cycle of the

clock. Calculate the resulting ripple voltage on either

output as follows:

VRIPPLE =

1

2

ILOAD

(1

/

fPUMP )

(1

/

CRESERVOIR )

where ILOAD is the load on either V+ or V-. For the typi-

cal fPUMP of 30kHz with 3.3µF reservoir capacitors, the

ripple is 25mV when ILOAD is 5mA. Remember that, in

most applications, the total load on V+ is the V+ load

current (IV+) and the current taken by the negative

charge pump (IV-).

Efficiency Considerations

Theoretically, a charge-pump voltage multiplier can

approach 100% power efficiency under the following

conditions:

• The charge-pump switches have virtually no offset

and extremely low on-resistance.

• The drive circuitry consumes minimal power.

• The impedances of the reservoir and pump capaci-

tors are negligible.

For the MAX865, the energy loss per clock cycle is the

sum of the energy loss in the positive and negative

converters, as follows:

LOSSCYCLE = LOSSPOS + LOSSNEG

=

1

2

C1

(V

+)2

−

2(V +) (VIN)

+

1 C2

2

(V +)2

−

(V

−)2





The average power loss is simply:

PLOSS = LOSSCYCLE x fPUMP

Resulting in an efficiency of:

( ) η = Total Output Power / Total Output Power − PLOSS

VIN

3.3µF

1 C1-

C1+ 8

2

3.3µF

3

C2- MAX865

C2-

V+ 7

IN 6

4 V-

GND 5

3.3µF

1 C1-

C1+ 8

2

3.3µF

3

C2+ MAX865

C2-

V+ 7

IN 6

4 V-

GND 5

OUT+

3.3µF

IN

GND

3.3µF

OUT-

Figure 3. Paralleling MAX865s

6 _______________________________________________________________________________________

Share Link: