MAX685EEE-T Maxim Integrated Products, MAX685EEE-T Datasheet - Page 9

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

Table 1. Component Values for the
Typical Operating Circuit
The resistor-divider formed by R4 and R3 sets the neg-
ative output voltage; the resistor-divider formed by R1
and R2 sets the positive output voltage. Let R4 be a
value near 100kΩ to set a resistor-divider current of
approximately 10µA. Determine the value of R3 by the
following:
Let R2 be a value near 100kΩ to set a resistor-divider
current of approximately 10µA. Determine the value of
R1 with the following formula:
C3, C4
D1, D2
REF
C1
C2
C5
L1
10µF, 10V
tantalum cap
0.22µF ceramic
capacitor
2.2µF ceramic
capacitor
47pF ceramic cap
0.1A, 20V
Schottky rectifier
22µH, 0.4A
inductor
DESCRIPTION
R1 = R2 x (V
R
3
_______________________________________________________________________________________
=
Setting the Output Voltage
R
OUT
4
Dual-Output (Positive and Negative),
Sprague 595D106X0010A2T or
AVX TAJA106K010R
Any manufacturer
Any manufacturer
Any manufacturer
Motorola MBR0520LT1 (0.5A)
or Central Semiconductor
CMPSH-3
Murata LHQ4N220J04 or
TDK NLC32522T-220K
+ - 1.24V) / 1.24
V
1 24
OUT
.
MANUFACTURER
DC-DC Converter for CCD and LCD
V
PART NUMBER
−
LXN and LXP may ring at the conclusion of each
switching cycle when the inductor current falls to zero.
Typically the ringing waveform appears only on LX_
and has no effect on output ripple and noise. If LX_
ringing is still objectionable, it may be damped by con-
necting a series RC in parallel with L1. Typically 1kΩ in
series with 100pF provides good damping with only 3%
efficiency degradation. See Figure 5.
Figure 5. LXN and LXP Waveforms with a Series-Connected
1kΩ Resistor and 100pF Capacitor Connected in Parallel with
L1 to Damp Ringing
TRANSISTOR COUNT: 902
SUBSTRATE CONNECTED TO GND
___________________Chip Information
LXP
LXN
Damping LX
0V
+5V
-7.5V
+15V
+5V
0V
9