MAX8726EUE+T Maxim Integrated Products, MAX8726EUE+T Datasheet - Page 12

• Manufacturer Part Number: MAX8726EUE+T
• Description: Display Drivers Triple-Output TFT-LC -LCD DC-DC Converter
• Manufacturer: Maxim Integrated Products

Specifications of MAX8726EUE+T

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The inductance value is then given by:
Considering the typical operating circuit, the maximum
DC load current (I
A 6.8µH inductance value is then chosen, based on the
above equations and using 85% efficiency and a 1MHz
operating frequency. Smaller inductance values typically
offer a smaller physical size for a given series resistance
and current rating, allowing the smallest overall circuit
dimensions. However, due to higher peak inductor
currents, the output voltage ripple (I
capacitor ESR) will be higher.
Use inductors with a ferrite core or equivalent; powder
iron cores are not recommended for use with the
MAX1748/MAX8726s’ high switching frequencies. The
inductor’s maximum current rating should exceed
I
reach up to 2.0A. The MAX1748/MAX8726s’ fast cur-
rent-limit circuitry allows the use of soft-saturation
inductors while still protecting the IC.
The inductor’s DC resistance significantly affects effi-
ciency. For best performance, select inductors with
resistance less than the internal n-channel FET resis-
tance. To minimize radiated noise in sensitive applica-
tions, use a shielded inductor.
The inductor should have as low a series resistance as
possible. For continuous inductor current, the power
loss in the inductor resistance, P
where R
A 10µF capacitor works well in most applications. The
equivalent series resistance (ESR) of the output-filter
capacitor affects efficiency and output ripple. Output
voltage ripple is largely the product of the peak induc-
tor current and the output capacitor ESR. Use low-ESR
ceramic capacitors for best performance. Low-ESR,
surface-mount tantalum capacitors with higher capacity
may be used for load transients with high peak cur-
rents. Voltage ratings and temperature characteristics
should be considered.
The input capacitor (C
current peaks drawn from the input supply and reduces
noise injection. The value of C
the source impedance of the input supply. High source
Triple-Output TFT-LCD
DC-DC Converters
12
PEAK
______________________________________________________________________________________
. Under fault conditions, inductor current may
L
L
=
is the inductor series resistance.
V
P
IN(MIN)
LR
V
(MAIN)
≅ (I
MAIN(MAX)
2
MAIN
×
2
Efficiency
×
IN
LIR
x V
) in boost designs reduces the
) is 200mA with a 10V output.
MAIN
×
I
IN
MAIN(MAX)
×
LR
is largely determined by
(V
/ V
MAIN
, is approximated by:
IN
PEAK
Output Capacitor
)
2
−
Input Capacitor
×
x R
V
f
OSC
IN(MIN)
x output filter
L
)
impedance requires high input capacitance, particularly
as the input voltage falls. Since step-up DC-DC convert-
ers act as “constant-power” loads to their input supply,
input current rises as input voltage falls. A good starting
point is to use the same capacitance value for C
C
The MAX1748/MAX8726 contain an internal current
integrator that improves the DC load regulation but
increases the peak-to-peak transient voltage (see the
load-transient waveforms in the Typical Operating
Characteristics). For highly accurate DC load regula-
tion, enable the current integrator by connecting a
470pF capacitor to INTG. To minimize the peak-to-peak
transient voltage at the expense of DC regulation, dis-
able the integrator by connecting INTG to REF and
adding a 100kΩ resistor to GND.
Use a Schottky diode with an average current rating
equal to or greater than the peak inductor current, and
a voltage rating at least 1.5 times the main output volt-
age (V
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OUT
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Coiltronics
Sumida USA
Toko
CAPACITORS
AVX
Kemet
Sanyo
Taiyo Yuden
DIODES
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International
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Motorola
Nihon
Zetex
SUPPLIER
. Table 1 lists suggested component suppliers.
MAIN
).
847-639-6400
561-241-7876
847-956-0666
847-297-0070
803-946-0690
408-986-0424
619-661-6835
408-573-4150
516-435-1110
310-322-3331
602-303-5454
847-843-7500
516-543-7100
PHONE
Integrator Capacitor
Rectifier Diode
847-639-1469
561-241-9339
847-956-0702
847-699-1194
803-626-3123
408-986-1442
619-661-1055
408-573-4159
516-435-1824
310-322-3332
602-994-6430
847-843-2798
516-864-7630
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IN
as for