Rainbow-electronics MAX1701 Manual de usuario descargar pdf (Pagina 12)

MAX1700/MAX1701

between the positive battery terminal and GND (Figure

5). The resistor values are then calculated as follows:

R3 = R4(V

LBN

-1)

where V

is the desired input voltage trip threshold

and V

LBN

= V

REF

= 1.25V. Since the input bias current

into LBP is less than 20nA, R4 can be a large value

(such as 270kΩ or less) without sacrificing accuracy.

The inputs have a common-mode input range from

0.5V to 1.5V and an input-referred hysteresis of 15mV.

The low-battery comparator can also be used to moni-

tor the output voltage, as shown in Figure 6.

To set the low-battery threshold to a voltage below the

1.25V reference, insert a resistor divider between REF

and LBN and connect the battery to the LBP input

through a 10kΩ current-limiting resistor (Figure 7). The

equation for setting the resistors for the low-battery

threshold is then as follows:

R5 = R6(V

REF

LBP

-1)

where V

LBP

is the desired voltage threshold. In Figures

5, 6, and 7, LBO goes low for a low-voltage input. The

low-battery comparator can be used to check the out-

put voltage or to control the load directly on P

OUT

dur-

ing start-up (Figure 8). Use the following equation to set

the resistor values:

R3 = R4(V

OUTTH

LBP

- 1)

where V

OUTTH

is the desired output-voltage trip point

and V

LBP

is connected to the reference or 1.25V.

1-Cell to 3-Cell, High-Power (1A),

Low-Noise, Step-Up DC-DC Converters

12 ______________________________________________________________________________________

FBPGNDGND

AO ARBITRARY VOLTAGE MONITOR

ARBITRARY

VOLTAGE

LOW-BATTERY MONITOR

VOLTAGE MONITOR

AIN

LBO

POK

OUT

POUT

LBP

LBN

REF

CLK/SEL

ONA

ONB

10Ω

0.22µF

0.7V TO 5.5V

MAX1701

Figure 5. Detecting Battery Voltage Above 1.25V

MAX1701

LBN

LBO

LBP

POUT

REF

GND

BATTERY

VOLTAGE

10k

0.22µF

MAX1701

LBO

REF

LBN

POUT

GND

0.22µF

OUT

LBP

Figure 6. Using the Low-Battery Comparator to Sense the

Output Voltage (MAX1701)

Figure 7. Detecting Battery Voltages Below 1.25V (MAX1701)

270k

MAX1701

LBP

LBO

LBN

0.22µF

OUT

POUT

10Ω

REF

GND

0.22µF

OUTPUT

Figure 8. Using the Low-Battery Comparator for Load Control

During Start-Up

1 2 ... 7 8 9 10 11 12 13 14 15 16

MAX1700/MAX1701 1

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