19-1353; Rev 0; 4/98
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
Dual Output Using a Single Inductor
Low-Noise Output, 30mVp-p Ripple
Output Voltages up to 24V and down to -9V
(up to 45V and down to -16V with added
Internal Switches in a Small Package
220kHz/400kHz Fixed-Frequency PWM Operation
Frequency Can Be Synchronized to
Selectable Power-On Sequencing
0.1µA Logic-Controlled Shutdown
The MAX685 DC-DC converter provides low-noise dual
outputs for powering CCD imaging devices and LCDs.
This device uses a single inductor to provide indepen-
dently regulated positive and negative outputs.
Integrated power switches are included in the small
16-pin QSOP package (same size as an 8-pin SO) to
save space and reduce cost.
Each output delivers up to 10mA from a +2.7V to +5.5V
input voltage range. Output voltages are set indepen-
dently up to 24V and down to -9V. With a few additional
low-cost components, the output voltages can be set at
up to 45V and down to -16V. Output ripple magnitude is
30mVp-p. The MAX685 uses a fixed-frequency, pulse-
width-modulated (PWM) control scheme at 220kHz or
400kHz to permit output noise filtering and to reduce
the size of external components. The frequency can
also be synchronized to an external clock signal
between 200kHz and 480kHz.
The MAX685 has a power-OK indicator output (POK)
that signals when both outputs are within regulation. A
logic-controlled shutdown completely turns off both out-
puts and reduces supply current to 0.1µA. The user
can also set which output turns on first.
The preassembled MAX685 evaluation kit is available to
reduce design time.
-40°C to +85°C
CCD Imaging Devices
2.7V TO 5.5V
Typical Operating Circuit
UP TO 24V,
DOWN TO -9V,
I.C. = INTERNALLY CONNECTED
Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.