200mA Step-Up Converters in 6-Pin

SOT23 and TDFN

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Detailed Description

The MAX8569A and MAX8569B compact high-efficien-

cy step-up converters feature low-quiescent supply cur-

rent to ensure the highest possible efficiency over a

wide load range. With a minimum 1.5V input voltage,

these devices are well suited for applications with two

alkaline cells, two nickel-metal-hydride (NiMH) cells, or

one lithium-ion (Li+) cell. When SHDN is low, the output

is connected to the battery through the inductor and an

internal p-channel MOSFET. This allows the input bat-

tery to be used as a backup or real-time clock supply

when the converter is off by eliminating the voltage drop

across the MOSFET body diode. These devices are

ideal for low-power applications where a small footprint

is critical. The internal synchronous rectifier improves

efficiency significantly and reduces size and cost by

eliminating the need for an external Schottky diode.

Control Scheme

The MAX8569A/MAX8569B feature a current-limited

control scheme that provides ultra-low quiescent current

and high efficiency over a wide output current range.

The switching cycles are not controlled by an oscillator.

Instead, switch on-time is terminated when the inductor

current reaches the 780mA (typ) n-channel current limit,

or when the 5µs maximum n-channel switch on-time is

reached. Following each on-cycle, the synchronous rec-

tifier turns on, shunts the MOSFET body diode, and the

inductor current ramps to zero before another cycle

begins. The next cycle occurs when the error compara-

tor senses that the output has fallen below the regulation

threshold.

Applications Information

Shutdown

Drive SHDN low to shut down the MAX8569A/

MAX8569B and reduce the input current to less than

1µA. During shutdown, the battery input is connected

to the output through the inductor and the internal syn-

chronous rectifier. This allows the input battery (rather

than a separate backup battery) to provide backup

power for devices such as an idled microcontroller,

SRAM, or real-time clock, without the usual diode for-

the IC for normal operation.

MAX8569A

FB

OUT

1.5V TO 3V

INPUT

L1

10

µH

C3

22

µF

C1

10

µF

3.3V OUTPUT

R4

100k

Ω

R3

168k

Ω

LX

4

1

2

5

6

3

SHDN

BATT

GND

C2

0.01

µF

R2

1M

Ω

R1

220k

Ω

Figure 1. Typical Application Circuit for MAX8569A

MAX8569B

OUT

1.5V TO 3V

INPUT

L1

10

µH

C3

22

µF

C1

10

µF

3.3V

OUTPUT

RESET

OUTPUT

R1

100k

Ω

LX

4

1

2

5

6

3

SHDN

BATT

GND

RST

OFF

ON

Figure 2. Typical Application Circuit for MAX8569B