MAX669EUB/V 데이터 시트보기 (PDF) - Maxim Integrated

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MAX669EUB/V

1.8V to 28V Input, PWM Step-Up Controllers in µMAX

Maxim Integrated 

1.8V to 28V Input, PWM Step-Up

Controllers in µMAX

Table 2. Bootstrapped and Non-Bootstrapped Configurations

CONFIGURATION FIGURE

USE

WITH:

INPUT

VOLTAGE

RANGE* (V)

OUTPUT

VOLTAGE

RANGE (V)

High-Voltage,

Bootstrapped

Figure

2

MAX669

1.8 to 28

3V to 28

Low-Voltage,

Bootstrapped

Figure

3

MAX669

1.8 to 5.5

2.7 to 5.5

High-Voltage,

Non-Bootstrapped

Figure

4

MAX668

3 to 28

VIN to ∞

Low-Voltage,

Non-Bootstrapped

Figure

5

MAX668

2.7 to 5.5

VIN to ∞

COMMENTS

Connect VCC to VOUT. Provides maximum external

FET gate drive for low-voltage (Input <3V) to high-

voltage (output >5.5V) boost circuits. VOUT cannot

exceed 28V.

Connect VOUT to VCC and LDO. Provides maxi-

mum possible external FET gate drive for low-volt-

age designs, but limits VOUT to 5.5V or less.

Connect VIN to VCC. Provides widest input and out-

put range, but external FET gate drive is reduced for

VIN below 5V.

Connect VIN to VCC and LDO. FET gate-drive

amplitude = VIN for logic-supply (input 3V to 5.5V) to

high-voltage (output >5.5V) boost circuits. IC oper-

ating power is less than in Figure 4, since IC current

does not pass through the LDO regulator.

Extra IC supply,

Non-Bootstrapped

None

MAX668

Not

Restricted

VIN to ∞

Connect VCC and LDO to a separate supply

(VBIAS) that powers only the IC. FET gate-drive

amplitude = VBIAS. Input power source (VIN) and

output voltage range (VOUT) are not restricted,

except that VOUT must exceed VIN.

* For standard step-up DC-DC circuits (as in Figures 2, 3, 4, and 5), regulation cannot be maintained if VIN exceeds VOUT. SEPIC

and transformer-based circuits do not have this limitation.

In addition to the configurations shown in Table 2, the

following guidelines may help when selecting a config-

uration:

1) If VIN is ever below 2.7V, VCC must be boot-

strapped to VOUT and the MAX669 must be used. If

VOUT never exceeds 5.5V, LDO may be shorted to

VCC and VOUT to eliminate the dropout voltage of

the LDO regulator.

2) If VIN is greater than 3.0V, VCC can be powered

from VIN, rather than from VOUT (non-bootstrapped).

This can save quiescent power consumption, espe-

cially when VOUT is large. If VIN never exceeds

5.5V, LDO may be shorted to VCC and VIN to elimi-

nate the dropout voltage of the LDO regulator.

3) If VIN is in the 3V to 4.5V range (i.e., 1-cell Li-Ion or

3-cell NiMH battery range), bootstrapping VCC from

VOUT, although not required, may increase overall

efficiency by increasing gate drive (and reducing

FET resistance) at the expense of quiescent power

consumption.

4) If VIN always exceeds 4.5V, VCC should be tied to

VIN, since bootstrapping from VOUT does not

increase gate drive from EXT but does increase

quiescent power dissipation.

12 ______________________________________________________________________________________

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