MAX685EEE Maxim Integrated Products, MAX685EEE Datasheet - Page 7

• Manufacturer Part Number: MAX685EEE
• Description: DC/DC Switching Converters DC/DC Converter for CCD & LCD
• Manufacturer: Maxim Integrated Products

The current into the LXN pin is sensed to measure the
inductor current. The MAX685 controls the inductor cur-
rent to regulate both the positive and negative output
voltages.
The SEQ pin controls the power-up sequence. If SEQ is
low, the positive output is disabled until the negative
output is within 90% of its regulation point. If SEQ is
high, the negative output is disabled until the positive
Figure 1. Functional Diagram
Figure 2. LXN and LXP Waveforms (see also Figure 5)
TO V
OUT+
LXN
LXP
TO V
_______________________________________________________________________________________
OUT-
SEQ and Power OK (POK)
REF
FBN
FBP
Dual-Output (Positive and Negative),
DC-DC Converter for CCD and LCD
NEGATIVE
POSITIVE
ERROR
ERROR
AMP
AMP
1.25V
REF
GND
+15V
0V
+5V
-7.5V
0V
MAX685
SYNC
SEQ
CONTROL
LOGIC
output is within 90% of its regulation point. The power-
OK output (POK) indicates that both output voltages
are in regulation. When both outputs are within 90% of
their regulation points, POK becomes high impedance.
Should one or both of the output voltages fall below
90% of their regulation points, POK pulls to ground.
POK can sink up to 2mA. To reduce current consump-
tion, POK is high impedance while the part is in shut-
down. When coming out of shutdown, POK remains
high impedance for 50ns (typ) before going low.
Connect POK to V
The MAX685 operates at a fixed switching frequency.
Set the operating frequency using the SYNC pin. If
SYNC is grounded, the part operates at the internally set
220kHz frequency. When SYNC is connected to V
the part operates at 400kHz. The MAX685 can also be
synchronized to signals between 200kHz and 480kHz.
Note that each output switches at half the oscillator or
synchronized frequency. Since the actual switching fre-
quency is one-half the applied clock signal, drive SYNC
at twice the desired switching frequency.
SHDN
POK
V
DD
P
N
VP
PGND
DD
through a 100kΩ resistor.
Synchronization/Internal
LXP
LXN
Frequency Selection
D1
D2
V
V
OUT-
OUT+
DD
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