MAX1883EUP-T Maxim Integrated, MAX1883EUP-T Datasheet - Page 26

• Manufacturer Part Number: MAX1883EUP-T
• Description: LCD Drivers Quad-Output TFT LCD DC-DC Converter with Buffer
• Manufacturer: Maxim Integrated

Specifications of MAX1883EUP-T

• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: TSSOP-20
• Mounting Style: SMD/SMT

Quad-Output TFT LCD DC/DC
Converters with Buffer
MAX1778/MAX1880–MAX1885
26
where η is the efficiency, f
cy (see the Electrical Characteristics ), and I
includes the primary load current and the input supply
currents for the charge pumps (see the Charge-Pump
Input Power and Efficiency Considerations section), lin-
ear regulator, and VCOM buffer. Considering the typi-
cal application circuit, the maximum average DC load
current (I
on the above equations and assuming 85% efficiency,
the inductance value is then chosen to be 4.7µH.
The inductor’s saturation current rating should exceed
the peak inductor current throughout the normal operat-
ing range. The peak inductor current is then given by:
Under fault conditions, the inductor current can reach
up to 1.85A (I
Characteristics ). However, the controller’s fast current-
limit circuitry allows the use of soft-saturation inductors
while still protecting the IC.
The inductor’s DC resistance can significantly affect
efficiency due to the power loss in the inductor. The
power loss due to the inductor’s series resistance (P
can be approximated by the following equation:
where R
formance, select inductors with resistance less than the
internal n-channel MOSFET on-resistance (0.35Ω typ).
Use inductors with a ferrite core or equivalent. To mini-
mize radiated noise in sensitive applications, use a
shielded inductor.
Output capacitor selection depends on circuit stability
and output-voltage ripple. A 10µF ceramic capacitor
works well in most applications (Tables 1 and 2).
Additional feedback compensation is required (see the
Feedback Compensation section) to increase the mar-
gin for stability by reducing the bandwidth further. In
cases where the output capacitance is sufficiently large,
additional feedback compensation is not necessary.
I
PEAK
L
MAIN(MAX)
P
is the inductor’s series resistance. For best per-
LR
=
≅
⎛
⎜
⎝
R
I
MAIN MAX MAIN
L
) is 300mA with an 8V output. Based
LIM(MAX)
⎛
⎜
⎝
I
MAIN
V
(
IN MIN
(
OSC
)
V
V
X V
IN
)
), see the Electrical
is the oscillator frequen-
MAIN
⎞
⎟
⎠
⎛
⎜
⎝
1
Output Capacitor
⎞
⎟
⎠
2
+
LIR
2
⎞
⎟
⎠
⎛
⎜
⎝
η
1
⎞
⎟
⎠
MAIN
LR
)
Output-voltage ripple has two components: variations
in the charge stored in the output capacitor with each
LX pulse, and the voltage drop across the capacitor’s
equivalent series resistance (ESR) caused by the
current into and out of the capacitor:
where I
Inductor Selection section). For ceramic capacitors, the
output-voltage ripple is typically dominated by V
PLE(C)
tics of the output capacitor must also be considered.
For stability, add a pole-zero pair from FB to GND in the
form of a compensation resistor (R
a compensation capacitor (C
2. Select R
feedback resistor.
The MAX1778/MAX1880–MAX1885 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 (ƒ
capacitor to INTG. To minimize the peak-to-peak tran-
sient voltage at the expense of DC regulation, disable
the integrator by connecting INTG to REF. When using
the MAX1883–MAX1885, connect a 100kΩ resistor to
GND when disabling the integrator.
The input capacitor (C
the current peaks drawn from the input supply and
reduces noise injection. The value of C
determined by the source impedance of the input sup-
ply. High source impedance requires high input capac-
itance, particularly as the input voltage falls. Since
step-up DC-DC converters 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
V
V
V
. The voltage rating and temperature characteris-
RIPPLE
RIPPLE ESR
RIPPLE C
PEAK
OSC
COMP
(
( )
is the peak inductor current (see the
=
= 1MHz)/1000pF (ƒ
to be half the value of R2, the low-side
)
≈
V
RIPPLE C
≈
⎛
⎜
⎝
V
I
MAIN
PEAK ESR COUT
IN
IN
V
( )
) in step-up designs reduces
MAIN
as for C
R
−
Feedback Compensation
+
COMP
V
V
IN
RIPPLE ESR
(
Integrator Capacitor
OUT
⎞
⎟
⎠
), as shown in Figure
COMP
⎛
⎜
⎝
C
.
OSC
OUT OSC
)
(
Input Capacitor
I
,
MAIN
AND
) in series with
Maxim Integrated
f
IN
)
= 500kHz)
is largely
⎞
⎟
⎠
RIP-