MAX1759EUB 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1759EUB

Buck/Boost Regulating Charge Pump in µMAX

Maxim Integrated 

Buck/Boost Regulating

Charge Pump in µMAX

Capacitor Selection

Optimize the charge-pump circuit for physical size, out-

put current, and output ripple by selecting capacitors

CIN, CX, and COUT. See Table 1 for suggested capacitor

values.

Note that capacitors must have low ESR (≤20mΩ) to

maintain low output ripple. Ceramic capacitors are

recommended. In cost-sensitive applications where high

output current is needed, the output capacitor may be a

combination of a 1µF ceramic in parallel with a 10µF tan-

talum capacitor. The ceramic capacitor’s low ESR will

help keep output ripple within acceptable levels.

Output Voltage Ripple

The MAX1759 proprietary control scheme automatically

chooses between voltage doubling and voltage step-

down to maintain output voltage regulation over various

load currents and VIN to VOUT voltage differentials.

When VIN is lower than VOUT, the charge pump always

operates in voltage-doubler mode. It regulates the output

voltage by modulating the charge delivered by the

transfer capacitor.

When VIN is higher than VOUT, the charge pump oper-

ates in voltage step-down mode, but may revert to volt-

age-doubler mode if necessary to maintain regulation

under load. While operating in step-down mode, the

output voltage ripple is typically much lower than it is in

voltage-doubler mode (see Typical Operating

Characteristics).

Output Current

The MAX1759 is guaranteed to deliver a regulated 3.3V

at 100mA continuous, from a +2.5V input. Peaks up to

200mA are acceptable as long as the current is

≤100mA (RMS).

Applications Information

PC Board Layout

The MAX1759 is a high-frequency switched-capacitor

voltage regulator. For best circuit performance, use a

ground plane and keep CIN, CX, COUT, and feedback

resistors (if used) close to the device. If using external

feedback, keep the feedback node as small as possi-

ble by positioning the feedback resistors very close to

FB. Suggested PC component placement and board

layout are shown in Figures 4a and 4b.

Chip Information

TRANSISTOR COUNT: 1802

0.33µF

CXN

VIN = 1.6V TO 5.5V

IN

CXP

OUT

10µF

MAX1759

POK

SHDN

GND

FB

PGND

VOUT = 2.5V

10µF

100k

R1

76.8k

R2

75k

Figure 3. Using External Feedback for Regulated 2.5V Output

Table 1. Capacitor Selection

OUTPUT

CURRENT

(mA)

100

100

50

CAPACITOR VALUE

CIN

CX

COUT

(µF)

(µF)

(µF)

10

0.33

10

4.7

0.22

4.7

2.2

0.1

2.2

OUTPUT RIPPLE

(mV)

VIN =

2.5V

40

80

100

VIN =

4.2V

20

60

80

8 _______________________________________________________________________________________

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