MAX619 Просмотр технического описания (PDF) - Maxim Integrated

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MAX619

Regulated 5V Charge-Pump DC-DC Converter

Maxim Integrated 

Regulated 5V Charge-Pump

DC-DC Converter

_____________________Pin Description

PIN NAME

FUNCTION

1 C1+ Positive Terminal for C1

2 IN Input Supply Voltage

3

OUT

+5V Output Voltage. VOUT = 0V when in

shutdown mode.

4 C2+ Positive Terminal for C2

5 C2- Negative Terminal for C2

6 GND Ground

7 SHDN Active-High CMOS Logic-Level Shutdown Input

8 C1- Negative Terminal for C1

_______________Detailed Description

Operating Principle

The MAX619 provides a regulated 5V output from a 2V

to 3.6V (two battery cells) input. Internal charge pumps

and external capacitors generate the 5V output, elimi-

nating the need for inductors. The output voltage is

regulated to 5V ±4% by a pulse-skipping controller that

turns on the charge pump when the output voltage

begins to droop.

To maintain the greatest efficiency over the entire input

voltage range, the MAX619’s internal charge pump

operates as a voltage doubler when VIN ranges from

3.0V to 3.6V, and as a voltage tripler when VIN ranges

from 2.0V to 2.5V. When VIN ranges from 2.5V to 3.0V,

the MAX619 switches between doubler and tripler

mode on alternating cycles, making a 2.5 x VIN charge

pump. To further enhance efficiency over the input

range, an internal comparator selects the higher of VIN

or VOUT to run the MAX619’s internal circuitry.

Efficiency with VIN = 2V and IOUT = 20mA is typically

80%.

Figure 1 shows a detailed block diagram of the

MAX619. In tripler mode, when the S1 switches close,

the S2 switches open and capacitors C1 and C2

charge up to VIN. On the second half of the cycle, C1

and C2 are connected in series between IN and OUT

when the S1 switches open and the S2 switches close,

as shown in Figure 1. In doubler mode, only C2 is

used.

During one oscillator cycle, energy is transferred from

the input to the charge-pump capacitors, and then

from the charge-pump capacitors to the output capaci-

tor and load. The number of cycles within a given time

frame increases as the load increases or as the input

supply voltage decreases. In the limiting case, the

charge pumps operate continuously, and the oscillator

frequency is nominally 500kHz.

Shutdown Mode

The MAX619 enters low-power shutdown mode when

SHDN is a logic high. SHDN is a CMOS-compatible

input. In shutdown mode, the charge-pump switching

action is halted, OUT is disconnected from IN, and

VOUT falls to 0V. Connect SHDN to ground for normal

operation. When VIN = 3.6V, VOUT typically reaches

5V in 0.5ms under no-load conditions after SHDN goes

low.

4 ________________________________________________________________________________________

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