19-1290; Rev 1; 2/98
Regulated, Adjustable -2x
Inverting Charge Pump
The MAX868 inverting charge pump provides a low-cost
and compact means of generating a regulated negative
voltage up to -2 x VIN from a positive input voltage
between 1.8V and 5.5V. It uses a pulse-frequency-
modulation (PFM) control scheme to generate the regulat-
ed negative output voltage. PFM operation is obtained
by gating the internal 450kHz oscillator on and off as
needed to maintain output voltage regulation. This
unique on-demand switching scheme gives the MAX868
excellent light-load efficiency without degrading its full-
load operation (up to 30mA), permitting smaller capaci-
tors to take advantage of the oscillator’s high switching
The MAX868 requires no inductors; only four capacitors
are required to build a complete DC-DC converter.
Output voltage regulation is achieved by adding just two
resistors. The MAX868 comes in a 10-pin µMAX pack-
age, which is only 1.11mm high and occupies just half
the board area of a standard 8-pin SO.
Small LCD Panels
o Regulated Negative Output Voltage
(up to -2 x VIN)
o Ultra-Small, 10-Pin µMAX Package
o On-Demand Switching at up to 450kHz
o 30µA Quiescent Supply Current
o Requires Only Four Small External Capacitors
o 1.8V to 5.5V Input Voltage Range
o 0.1µA Logic-Controlled Shutdown
o Up to 30mA Output Current
0°C to +70°C
-40°C to +85°C
*Dice are tested at TA = +25°C.
Typical Operating Circuit
VIN = 1.8V TO 5.5V
VOUT = 0V TO -2 x VIN
________________________________________________________________ Maxim Integrated Products 1
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