Rainbow-electronics MAX1804 Manual do Utilizador descarregar pdf (Página 7)

MAX1804

External Four-Input Feedback Integrator for

Power Supplies

_______________________________________________________________________________________ 7

The MAX1804 only sinks current at OUT (Figure 4). The

maximum sink current and maximum regulator voltage

increase are limited by the minimum guaranteed OUT

current of 10µA. The maximum regulator output voltage

increase can be further limited by including a resistor

between OUT and the feedback point of the regulator.

If any of the IN_ inputs fall to 90% of the regulation set

point, they are automatically disabled and OUT contin-

ues to regulate according to the lowest remaining

active input. See Automatic Input Disable.

Adjusting the Regulation Set Point

The MAX1804 monitors the voltage at the IN1–IN4

sense inputs and regulates the lowest active input to

four times the reference voltage at ADJ. The IN1–IN4

regulation set point is calculated as:

IN_

= 4

ADJ

The total error in the MAX1804 regulation set point is:

total percentage error = [(IN_scale factor x V

ADJ

IN_offset) / (4 x V

ADJ

)] x 100%

The maximum IN_ voltage is 5.5V. Use the MAX1804 for

higher output voltages by using an external divider to

divide down the desired output voltage at the IN1–IN4

pins. Since the IN_ input bias current is fairly high (1.5µA

typ), choose the resistive divider accordingly.

Automatic Input Disable

The MAX1804 has an input buffer stage that monitors

the sense inputs (IN1–IN4) and connects the lowest to

its internal integrator (Figure 4). Each input is com-

pared to 90% of the set point. If the input falls below

this value, the input buffer is disabled and the output

voltage is adjusted according to the lowest of the

remaining active inputs (see Automatic Input Disable in

Typical Operating Characteristics). If all four sense

4.5V TO 28V

VIN

VOUT

SHDN

SYNC

REF

10 16

BST

PGND

CSH

CSL

V+

SHDN

N1B

IRF7303

CMPSH-3

0.1µF

N1A

IRF7303

MBR0530

SKIP

SYNC

REF

GND

JU3

JU4

EXT

REF

COMP

ADJ

IN2

IN3

IN4

IN1

OUTV+

0.01µF

0.33µF

100k

JU2

JU1

0.1µF

22µF

35V

220µF

10V

TOP

91k

5V± 5%

PFET

LOAD

BOTTOM

100k

562k

4.7µF

16V

15µH

0.033Ω

MAX1653

MAX1804

SHDN

Figure 2. Application Circuit with Step-Down Regulator

1 2 3 4 5 6 7 8 9 10 11

Power Supplies 1

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