Detailed Description

The MAX1673 new-generation, high-output-current,

regulated charge-pump DC-DC inverter provides up to

125mA. Designed specifically for compact applica-

tions, a complete regulating circuit requires only three

small capacitors and two resistors. The MAX1673

employs On-Demand™ regulation circuitry, providing

output regulation modes optimized for either lowest out-

put noise or lowest supply current. In addition, the

MAX1673 includes shutdown control.

In Linear (LIN) mode or when heavily loaded in Skip

mode, the charge pump runs continuously at 350kHz.

During one-half of the oscillator period, switches S1 and

S2 close (Figure 2), charging the transfer capacitor

IN). During the other half cycle, switches S3 and S4

output capacitor (CAP+ = GND, CAP- = OUT).

Regulated, 125mA-Output,

Charge-Pump DC-DC Inverter

6

_______________________________________________________________________________________

______________________________________________________________Pin Description

MAX1673

IN

INPUT

5.0V

OUTPUT

-3V

10

µF

22

µF

2.2

µF

LIN/SKIP

FB

R1

100k

R1

60.4k

OUT

GND

CAP+

ON

OFF

4

2

3

SHDN

CAP-

LIN

SKIP

1

7

5

6

8

Figure 1. Standard Application Circuit

S2

OUT

S1

CAP+

CAP-

IN

S4

S3

350kHz

S2

OUT

S1

IN

S4

S3

350kHz

CAP+

CAP-

Inverting Charge-Pump Output

OUT

5

Feedback Input. Connect FB to a resistor-divider from IN (or other reference source) to OUT for regulated

output voltages (Figures 1 and 4).

FB

6

Ground

GND

7

Power-Supply Positive Voltage Input

IN

8

Shutdown Control Input. Drive SHDN low to shut down the MAX1673. Connect SHDN to IN for normal

operation. OUT connects to GND through a 1

Ω (typical) resistor in shutdown mode.

SHDN

4

Negative Terminal of Flying Capacitor

CAP-

3

PIN

Positive Terminal of Flying Capacitor

CAP+

2

Regulation-Mode Select Input. Driving LIN/SKIP high or connecting it to IN selects LIN mode, with regula-

tion accomplished by modulating switch resistance. Driving LIN/SKIP low or connecting it to GND selects

Skip mode, where the device regulates by skipping charge-pump pulses.

LIN/SKIP

1

FUNCTION

NAME