MAX17014EVKIT+ Maxim Integrated Products, MAX17014EVKIT+ Datasheet - Page 30

• Manufacturer Part Number: MAX17014EVKIT+
• Description: KIT EVAL FOR MAX17014
• Manufacturer: Maxim Integrated Products

Specifications of MAX17014EVKIT+

• Main Purpose: Special Purpose DC/DC, LCD Supply
• Outputs And Type: 4, Non-Isolated
• Power - Output: 32.9W
• Voltage - Output: 3.3V, 16V, -6V, 35V
• Current - Output: 2A, 1.5A, 100mA, 50mA
• Voltage - Input: 10.8 ~ 13.2V
• Regulator Topology: Boost, Buck
• Frequency - Switching: 1.2MHz
• Board Type: Fully Populated
• Utilized Ic / Part: MAX17014
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Increasing the flying capacitors (connected to DRVN
and DRVP) value lowers the effective source impedance
and increases the output-current capability. Increasing
the capacitance indefinitely has a negligible effect on
output-current capability because the internal switch
resistance and the diode impedance place a lower limit
on the source impedance. A 0.1µF ceramic capacitor
works well in most low-current applications. The flying
capacitor’s voltage rating must exceed the following:
where n is the stage number in which the flying capaci-
tor appears.
Increasing the output capacitance or decreasing the
ESR reduces the output ripple voltage and the peak-to-
peak transient voltage. With ceramic capacitors, the
output voltage ripple is dominated by the capacitance
value. Use the following equation to approximate the
required capacitor value:
where C
pump, I
pump, and V
output ripple.
Adjust the positive charge-pump regulator’s output volt-
age by connecting a resistive voltage-divider from the
SRC output to GND with the center tap connected to
FBP (Figure 1). Select the lower resistor of divider R17
in the 10kΩ to 30kΩ range. Calculate the upper resis-
tor, R16, with the following equation:
where V
Adjust the negative charge-pump regulator’s output
voltage by connecting a resistive voltage-divider from
V
(Figure 1). Select R2 in the 20kΩ to 50kΩ range.
Calculate R1 with the following equation:
where V
only source up to 50µA, using a resistor less than 20kΩ
for R1 results in higher bias current than REF can supply.
Low-Cost Multiple-Output
Power Supply for LCD TVs
30
GOFF
______________________________________________________________________________________
to REF with the center tap connected to FBN
FBN
FBP
OUT
LOAD
= 1.25V (typ).
= 250mV, V
_
C
RIPPLE_CP
CP
_
OUT CP
CP
R
R
1
is the output capacitor of the charge
17
=
_
is the load current of the charge
R
V
=
2
Charge-Pump Output Capacitor
CX
R
×
≥
is the peak-to-peak value of the
16
REF
2
V
> ×
V
FBN
f
OSC RIPPLE CP
×
n V
REF
⎛
⎜
⎝
= 1.25V. Note that REF can
I
Output Voltage Selection
LOAD CP
V
V
−
V
GON
FBP
−
SUP
V
V
GOFF
FBN
_
−
Flying Capacitors
1
⎞
⎟
⎠
_
Careful PCB layout is important for proper operation.
Use the following guidelines for good PCB layout:
•
•
Minimize the area of respective high-current loops
by placing each DC-DC converter’s inductor,
diode, and output capacitors near its input capaci-
tors and its LX_ and GND_ pins. For the step-down
regulator, the high-current input loop goes from the
positive terminal of the input capacitor to the IC’s IN
pin, out of LX2, to the inductor, to the positive termi-
nals of the output capacitors, reconnecting the out-
put capacitor and input capacitor ground terminals.
The high-current output loop is from the inductor to
the positive terminals of the output capacitors, to
the negative terminals of the output capacitors, and
to the Schottky diode (D2). For the step-up regula-
tor, the high-current input loop goes from the posi-
tive terminal of the input capacitor to the inductor,
to the IC’s LX1 pin, out of GND1, and to the input
capacitor’s negative terminal. The high-current out-
put loop is from the positive terminal of the input
capacitor to the inductor, to the output diode (D1),
to the positive terminal of the output capacitors,
reconnecting between the output capacitor and
input capacitor ground terminals. Connect these
loop components with short, wide connections.
Avoid using vias in the high-current paths. If vias
are unavoidable, use many vias in parallel to
reduce resistance and inductance.
Create a power ground island for the step-down reg-
ulator, consisting of the input and output capacitor
grounds and the diode ground. Connect all these
together with short, wide traces or a small ground
plane. Similarly, create a power ground island
(GND1) for the step-up regulator, consisting of the
input and output capacitor grounds and the GND1
pin. Create a power ground island (CPGND) for the
positive and negative charge pumps, consisting of
SUP and output (SRC, V
and negative charge-pump diode ground. Connect
CPGND ground plane to GND1 ground plane
together with wide traces. Maximizing the width of
the power ground traces improves efficiency and
reduces output voltage ripple and noise spikes.
Create an analog ground plane (GND) consisting of
the GND pin, all the feedback divider ground con-
nections, the COMP and DEL capacitor ground
connections, and the device’s exposed backside
pad. Connect GND1 and GND islands by connect-
ing the two ground pins directly to the exposed
backside pad. Make no other connections between
the GND1 and GND ground planes.
PCB Layout and Grounding
GOFF
) capacitor grounds,