MAX17062 Maxim Integrated Products, MAX17062 Datasheet - Page 10

• Manufacturer Part Number: MAX17062
• Description: TFT-LCD Step-Up DC-DC Converter
• Manufacturer: Maxim Integrated Products

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The input capacitor (C
drawn from the input supply and reduces noise injection
into the IC. Two 4.7μF ceramic capacitors are used in
the Typical Operating Circuit (Figure 1) because of the
high source impedance seen in typical lab setups.
Actual applications usually have much lower source
impedance since the step-up regulator often runs
directly from the output of another regulated supply.
Typically, C
the typical operating circuit. Ensure a low-noise supply
at IN by using adequate C
age variation can be tolerated on C
from C
Figure 1).
The MAX17062’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommend-
ed for most applications because of their fast recovery
time and low forward voltage. The diode should be
rated to handle the output voltage and the peak switch
current. Make sure that the diode’s peak current rating
is at least I
section and that its breakdown voltage exceeds the
output voltage.
The MAX17062 operates with an adjustable output from
V
output (V
to FB (see Figure 1). Select R2 in the 10kΩ to 50kΩ
range. Calculate R1 with the following equation:
where V
is 1.24V (typ). Place R1 and R2 close to the IC.
The voltage feedback loop needs proper compensation
to prevent excessive output ripple and poor efficiency
caused by instability. This is done by connecting a
resistor (R
COMP to AGND, and another capacitor (C
COMP to AGND. R
frequency integrator gain for fast transient response,
TFT-LCD Step-Up DC-DC Converter
10
IN
to 20V. Connect a resistive voltage-divider from the
______________________________________________________________________________________
IN
FB
MAIN
using an RC lowpass filter (see R1 and C3 in
COMP
, the step-up regulator’s feedback set point,
IN
PEAK
) to AGND with the center tap connected
can be reduced below the values used in
R
1
) and capacitor (C
calculated in the Inductor Selection
=
COMP
R
2
IN
×
) reduces the current peaks
IN
⎛
⎜
⎝
is chosen to set the high-
Input Capacitor Selection
V
. Alternatively, greater volt-
Output Voltage Selection
Rectifier Diode Selection
MAIN
V
Loop Compensation
FB
COMP
IN
−
if IN is decoupled
1
⎞
⎟
⎠
) in series from
COMP2
) from
while C
maintain loop stability. The second capacitor, C
is chosen to cancel the zero introduced by output-
capacitance ESR. For optimal performance, choose the
components using the following equations:
For the ceramic output capacitor, where ESR is small,
C
compensation is by inspecting the transient response
of the MAX17062. Adjust R
sary to obtain optimal transient performance.
The soft-start capacitor should be large enough that it
does not reach final value before the output has
reached regulation. Calculate C
where C
any bypass capacitor on the output bus, V
maximum output voltage, I
current allowed, I
during power-up, and V
The load must wait for the soft-start cycle to finish
before drawing a significant amount of load current.
The duration after which the load can begin to draw
maximum load current is:
COMP2
C
COMP
R
C
COMP
COMP
OUT
COMP
is optional. The best gauge of correct loop
C
⎛
⎜
⎜ ⎜
⎝
2
V
SS
IN
≈
is the total output capacitance including
is chosen to set the integrator zero to
≈
>
×
t
0 0036
≈
V
MAX
.
OUT
OUT
I
21
315
INRUSH
10
= 2.4 x 10
×
2
×
is the maximum output current
×
IN
×
10
−
I
L
MAIN MAX
V
is the minimum input voltage.
V
COMP
R
−
OUT
IN
V
−
×
6
INRUSH
IN
ESR
V
IN
Soft-Start Capacitor
I
I
OUT
×
×
(
MAIN MAX
SS
×
5
×
×
and C
V
C
V
x C
×
OUT
OUT
V
to be:
OUT
C
)
OUT
(
×
L
is the peak inrush
SS
OUT
×
×
V
COMP
OUT
×
R
×
)
I
COMP
MAIN MAX
C
OUT
⎞
⎟
⎟ ⎟
⎠
OUT
as neces-
(
COMP2
is the
)
,