Detailed Description

The MAX1697 capacitive charge pumps invert the volt-

age applied to their input. For highest performance, use

low equivalent series resistance (ESR) capacitors (e.g.,

ceramic).

During the first half-cycle, switches S2 and S4 open,

switches S1 and S3 close, and capacitor C1 charges to

the voltage at IN (Figure 2). During the second half-

cycle, S1 and S3 open, S2 and S4 close, and C1 is level

allel with the reservoir capacitor C2. If the voltage across

C2 is smaller than the voltage across C1, charge flows

from C1 to C2 until the voltage across C2 reaches

load drains charge from C2.

Efficiency Considerations

The efficiency of the MAX1697 is dominated by its qui-

is given by:

η≅

+

−









⋅

I

II

IR

V

OUT

OUT

Q

OUT

OUT

IN

1

60mA, SOT23 Inverting Charge Pump

with Shutdown

_______________________________________________________________________________________

7

0

100

50

200

150

300

250

350

450

400

500

0

234

1

567

9

810

MAX1697T

OUTPUT RIPPLE vs. CAPACITANCE

CAPACITANCE (

µF)

0

100

50

200

150

300

250

350

450

400

500

0

234

1

567

9

810

MAX1697U

OUTPUT RIPPLE vs. CAPACITANCE

CAPACITANCE (

µF)

Pin Description

6

Positive Terminal of the Flying

Capacitor

1

Inverting Charge-Pump Output

2

Power-Supply Voltage Input. Input

range is 1.5V to 5.5V.

3

Negative Terminal of the Flying

Capacitor

4

Ground

5

Shutdown Input. Drive this pin high

for normal operation; drive it low for

shutdown mode. OUT is actively

pulled to ground during shutdown.

PIN

FUNCTION

NAME

C1+

OUT

IN

C1-

GND

SHDN

Typical Operating Characteristics (continued)

TE: (

C1

C2

21

5

ON

OFF

3

6

4

C3

C1+

C1-

IN

SHDN

OUT

GND

INPUT

1.5V to 5.5V

NEGATIVE

OUTPUT

MAX1697

Figure 1. Typical Application Circuit