MAX686EEE+ Maxim Integrated Products, MAX686EEE+ Datasheet - Page 12

• Manufacturer Part Number: MAX686EEE+
• Description: IC SUPPLY LCD BIAS INV 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost), Invertingr

Specifications of MAX686EEE+

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: ±27.5V
• Current - Output: 100mA
• Frequency - Switching: 300kHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX686’s high switching frequency demands a
high-speed rectifier. Schottky diodes, such as the
1N5818 or MBR0530L, are recommended. Make sure
that the diode’s peak current rating exceeds the peak
current set by ISET and that its breakdown voltage
exceeds the output voltage. Schottky diodes are pre-
ferred due to their low forward voltage. However, ultra-
high-speed silicon rectifiers are also acceptable. Table 1
lists Schottky diode suppliers.
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
12
Figure 4. Feed-Forward Capacitor
Table 1. Component Suppliers
CAPACITORS
DIODES
INDUCTORS
AVX: TPS series
Matsuo: 267 series
Sprague 595D series
Motorola: MBR0530L
Nihon; EC11 FS1 series
Coilcraft: DO1608 and
DT1608 series
Murata-Erie: LQH4
series
Sumida: CD43, CD54,
and CD74 series
TDK: NLC565050 series
V
TO 27.5V
IN
V
CC
= 0.8V
TO 5.5V
______________________________________________________________________________________
= 2.7V
SUPPLIER
0.1 F
15 F
V
CC
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MAX686
22 H
PHONE
DACOUT
LX
FB
Selecting Diodes
MBR0530L
R3
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[phone]
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R1
R2
FAX
V
OUT
C
F
The primary selection criterion for the output filter
capacitor is low equivalent series resistance (ESR). The
product of the peak inductor current and the output fil-
ter capacitor’s ESR determines the amplitude of the
high-frequency ripple seen on the output voltage.
These requirements can be balanced by appropriately
selecting the current limit, as discussed in the Setting
the Peak Inductor Current Limit section. Table 1 lists
some low-ESR capacitor suppliers.
Although the output current of many MAX686 applica-
tions may be relatively small, the input supply must be
able to source current transients equal to the ISET cur-
rent limit. The input bypass capacitor reduces the peak
currents drawn from the voltage source and reduces
noise caused by the MAX686’s switching action. The
input source impedance determines the size of the
capacitor required at the input (V
filter capacitor, low ESR is the primary consideration. A
15µF, low-ESR capacitor is adequate for most applica-
tions, although smaller bypass capacitors may also be
acceptable in light-load applications. Bypass the IC
separately with a 0.1µF ceramic capacitor placed as
close as possible to the V
Bypass REF to GND with a 0.1µF ceramic capacitor for
REF currents up to 25µA. REF can source up to 50µA of
current for external loads. For 25µA ≤ I
bypass REF with a 0.47µF capacitor.
Figure 5. Using a Potentiometer to Adjust Output Voltage
V
TO 27.5V
IN
= 0.8V
V
CC
TO 5.5V
= 2.7V
0.1 F
15 F
V
CC
MAX686
22 H
CC
REF
LX
FB
Selecting Capacitors
and GND pins.
Output Filter Capacitors
IN
). As with the output
Bypass Capacitors
100k
POTENTIOMETER
R
POT
MBR0530L
R3
REF
R1
R2
≤ 50µA,
V
OUT
C
F