MAX17127 Maxim Integrated Products, MAX17127 Datasheet - Page 20

• Manufacturer Part Number: MAX17127
• Description: Six-String WLED Driver
• Manufacturer: Maxim Integrated Products

The current through each FB_ pin is controlled only
during the step-up converter’s on-time. During the con-
verter off-time, the current sources are turned off. The
output voltage does not discharge and stays high. The
MAX17127 disables the FB_ current source, which the
string is shorted. In this case, the step-up converter’s
output voltage is always applied to the disabled FB_ pin.
The FB_ pin can withstand 45V.
Careful PCB layout is important for proper operation.
Use the following guidelines for good PCB layout:
1) Minimize the area of high-current switching loop of
2) Connect high-current input and output components
Six-String WLED Driver with Integrated
Step-Up Converter
20
rectifier diode, internal MOSFET, and output capaci-
tor to avoid excessive switching noise.
with short and wide connections. The high-current
input loop goes from the positive terminal of the input
capacitor to the inductor, to the internal MOSFET,
and then to the input capacitor’s negative terminal.
The high-current output loop is from the positive ter-
minal of the input capacitor to the inductor, to the rec-
tifier diode, and to the positive terminal of the output
capacitors, reconnecting between the output capaci-
tor and input capacitor ground terminals. Avoid using
vias in the high-current paths. If vias are unavoidable,
use multiple vias in parallel to reduce resistance and
inductance.
_____________________________________________________________________________________
FB Pin Maximum Voltage
PCB Layout Guidelines
3) Create a ground island (PGND) consisting of the
4) Place the overvoltage-detection divider resistors as
5) Place the V
6) Minimize the size of the SW node while keeping it
Refer to the MAX17127 Evaluation Kit data sheet for an
example of proper board layout.
input and output capacitor ground. Connect all
these together with short, wide traces or a small
ground plane. Maximizing the width of the power
ground traces improves efficiency and reduces out-
put voltage ripple and noise spikes. Create an analog
ground island (AGND) consisting of the overvoltage
detection divider (R1 and R2) ground connection; the
ISET, FSLCT, COMP resistor connections; and the
device’s exposed backside pad. Connect the AGND
and PGND islands by connecting the AGND pins
directly to the exposed backside pad. Make no other
connections between these separate ground planes.
close to the OVP pin as possible. The divider’s center
trace should be kept short. Placing the resistors far
away causes the sensing trace to become antennae
that can pick up switching noise. Avoid running the
sensing traces near SW.
tors as close to the device as possible. The ground
connection of the bypass capacitors should be con-
nected directly to AGND pins with a wide trace.
wide and short. Keep the SW node away from the
feedback node and ground. If possible, avoid run-
ning the SW node from one side of the PCB to the
other. Use DC traces as a shield if necessary.
IN
pin and V
DDIO
pin bypass capaci-
www.DataSheet4U.com