MAX629 Ver la hoja de datos (PDF) - Maxim Integrated

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Fabricante

MAX629

28V, Low-Power, High-Voltage, Boost or Inverting DC-DC Converter

Maxim Integrated 

28V, Low-Power, High-Voltage,

Boost or Inverting DC-DC Converter

POL

REF

1.25V

REF

FB

ERROR

AMP

MIN OFF-TIME

GENERATOR

POLARITY TRIG

START-UP Q

F/F

S

Q

R

MAX629

LX

START-UP

COMPARATOR

ISET

SHDN

VCC

1V

CONTROL

TRIG

MAX ON-TIME

GENERATOR

(10µs)

Q

GND

Figure 1. Functional Diagram

without a significant loss of accuracy. Begin by select-

ing R2 to be in the 10kΩ to 200kΩ range, and calculate

R1 using the applicable equation from the following

subsections.

Positive Output Voltages

For positive output voltages, use the typical boost con-

figuration shown in Figure 2, connecting POL to GND.

This sets the threshold voltage at FB to equal VREF.

Choose the value of R2 and calculate R1 as follows:

R1

= R2

x





VOUT

VREF

−



1

where VREF = 1.25V.

Negative Output Voltages

For negative output voltages, configure R1 and R2 as

shown in Figure 3, connecting POL to VCC. This sets

the FB threshold voltage to GND so that negative volt-

ages can be regulated. Choose R2 and calculate R1 as

follows:

R1 = R2 x | VOUT |

VREF

where VREF = 1.25V.

Figure 3 demonstrates generation of a negative output

voltage by following the MAX629 with an inverting

charge pump. This configuration limits VOUT to values

between -VIN and -28V. If smaller negative output volt-

ages are required, D2’s cathode can be connected to

VIN. This alternative configuration permits output volt-

ages smaller than -VIN, but cannot be used for output

voltages more negative than -28V - VIN. It produces

roughly one-half the output current as the standard con-

figuration and is typically 5% less efficient.

6 _______________________________________________________________________________________

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