MAX1686 データシートの表示（PDF） - Maxim Integrated

部品番号

コンポーネント説明

一致するリスト

MAX1686

3V to 5V Regulating Charge Pumps for SIM Cards

Maxim Integrated 

3V to 5V Regulating

Charge Pumps for SIM Cards

1µA. Other features include soft-start, undervoltage

lockout, and short-circuit protection.

Charge-Pump Control

Figure 2 shows an idealized, unregulated charge-pump

voltage doubler. The oscillator runs at a 50% duty

cycle. During one half of the period, the transfer capac-

itor (CX) charges to the input voltage. During the other

half, the doubler stacks the voltage across CX and the

input voltage, and transfers the sum of the two voltages

to the output filter capacitor (COUT). The MAX1686 uses

Skip Mode control to regulate its output voltage and to

achieve good efficiency over a large output current

range. When the comparator detects that the output

voltage is too low, the 1MHz oscillator is enabled and

CX is switched. When the output voltage is above regu-

lation, the oscillator is disabled and CX is connected at

the input.

Soft-Start

In the 5V mode (3/5 = GND), the start-up current is lim-

ited by the soft-start control to typically 200mA, inde-

pendent of the load. Until the output voltage reaches

VIN / 2, the input is connected to the output through a

50Ω series P-channel MOSFET and the charge pump

is disabled. For VIN / 2 < VOUT < 4.75V (5.00V for

MAX1686H) and for a maximum of 2ms the charge

pump is active, but RON of the switch S2 is limited to

50Ω. This limits typical current surges associated with

charge pumps at start-up. When soft-start is complete,

VOUT > 4.75V (5.00V for MAX1686H) or 2ms (whichever

occurs first), switch S2’s on-resistance is decreased to

minimize losses.

In 3V mode (3/5 = IN), the start-up current is limited by

the 50Ω series P-channel MOSFET connected between

IN and OUT until the output voltage reaches VIN / 2. For

VOUT > VIN / 2, RON is reduced to 2.5Ω.

With a 500Ω load the device turns on in less than 1.5ms

(see Typical Operating Characteristics for graphs of

start-up waveforms).

Shutdown Mode

Driving SHDN low places the device in shutdown mode,

which disables the oscillator, the control logic, and the

reference. Placing the device in shutdown mode

reduces the no-load supply current to less than 1µA; the

output is actively discharged through the internal N-

channel FET and disconnected from the input. In normal

operation, SHDN is driven high or connected to IN.

Applications Information

Capacitor Selection

The MAX1686 requires only three external capacitors.

The capacitor values are closely linked to the output

current capability, noise, and switching frequency. The

1MHz oscillator frequency minimizes capacitor size

compared to lower-frequency charge pumps.

Generally, the transfer capacitor (CX) will be the

smallest, the input capacitor (CIN) will be twice the size

of CX, and the output capacitor (COUT) can be from 10

to 50 times CX. The suggested capacitor values are

CIN = 0.1µF, CX = 0.047µF, and COUT = 2.2µF as

shown in Figure 3. For input voltages as low as 2.7V,

the following values are recommended: CIN = 0.47µF,

CX = 0.22µF, and COUT = 10µF. Table 1 lists the perfor-

CX

CXN

CXP

IN

S1

S2

CIN

OSC

CX

0.047µF

6

7

OUT

INPUT

2.85V TO 4.2V

CXN

3 IN

CXP

OUT 8

OUTPUT

VIN OR 4.75V AT 20mA

CIN

COUT

0.1µF

MAX1686

2.2µF

(CERAMIC)

COUT

2 SHDN

3V

5V

1 3/5

GND

PGND

4

5

GND

Figure 2. Unregulated Voltage Doubler

Figure 3. Standard Application Circuit

6 _______________________________________________________________________________________

Share Link: