HWD20012 datasheet(9/13 Pages) ETC1

9 / 13 page

Selecting the Output Voltage

VOUT can be set to 3.3V or 5.0V by connecting the FB

pin to GND (5V) or OUT (3.3V) (Figures 5 and 6).

To adjust the output voltage, connect a resistor-divider

from VOUT to FB to GND (Figure 7). Choose a value

less than 260k

Ω for R6. Use the following equation to

calculate R5:

R5 = R6 [(VOUT / VREF ) - 1]

where VREF = +1.3V and VOUT may range from 2V to

5V. The input bias current of FB has a maximum value

of 50nA which allows large-value resistors (R6

≤ 260kΩ)

to be used.

Low-Battery Detection

The HWD20011/HWD2001/HWD20012 contain an on-chip

comparator for low-battery detection. If the voltage at

LBI falls below the internal reference voltage (1.30V),

LBO (an open-drain output) sinks current to GND. The

low-battery monitor threshold is set by two resistors, R3

and R4 (Figures 5, 6, and 7). Since the LBI current is

less than 50nA, large resistor values (R4

≤ 260kΩ) can

be used to minimize loading of the input supply.

Calculate R3 using the following equation:

R3 = R4 [(VTRIP / VREF) - 1]

for VTRIP

≥ 1.3V. VTRIP is the level where the low-battery

detector output goes low, and VREF is the internal

1.30V reference. Connect a pull-up resistor of 100k

Ω or

greater from LBO to OUT when driving CMOS circuits.

LBO is an open-drain output, and can be pulled as

high as 6V regardless of the voltage at OUT. When LBI

is above the threshold, the LBO output is high imped-

ance. If the low-battery comparator is not used, ground

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

HWD20011

HWD2001

HWD20012

BATT

(HWD20012)

VIN

LBI

REF

GND

200

Ω

100k

µF

µH

0.1

µF

LBO

0.1

µF

OUTPUT

+3.3V

VOUT

LOW-BATTERY

OUTPUT

SHDN

OUT

CLSEL

(HWD20012)

Figure 5. Preset Output Voltage of +3.3V

HWD20011

HWD2001

HWD20012

BATT

(HWD20012)

VIN

LBI

REF

GND

200

Ω

100k

µH

µF

0.1

µF

LBO

OUTPUT

2V to 5.5V

SHDN

OUT

CLSEL

(HWD20012)

LOW-

BATTERY

OUTPUT

0.1

µF

Figure 7. Setting an Adjustable Output

HWD20011

HWD2001

HWD20012

BATT

(HWD20012)

VIN

LBI

REF

GND

200

Ω

100k

µH

µF

0.1

µF

LBO

0.1

µF

OUTPUT

5.0V

SHDN

OUT

CLSEL

(HWD20012)

LOW-

BATTERY

OUTPUT

Figure 6. Preset Output Voltage of +5V

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