MAX8790ETP+ Maxim Integrated Products, MAX8790ETP+ Datasheet - Page 21

• Manufacturer Part Number: MAX8790ETP+
• Description: IC LED DRVR WHITE BCKLGT 20-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LEDr

Specifications of MAX8790ETP+

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: No
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 1MHz
• Voltage - Supply: 4.5 V ~ 5.5 V, 5.5 V ~ 26 V
• Voltage - Output: 5V
• Mounting Type: Surface Mount
• Package / Case: 20-TQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 25mA
• Internal Switch(s): Yes
• Low Level Output Current: 1000000 uA (Typ)
• High Level Output Current: 25.75 mA
• Operating Supply Voltage: 4.5 V to 26 V
• Maximum Supply Current: 2 mA
• Maximum Power Dissipation: 1349 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Efficiency: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Careful PCB layout is important for proper operation. Use
the following guidelines for good PCB layout:
1) Minimize the area of the high current-switching loop
2) Connect high-current input and output components
3) Create a ground island (PGND) consisting of the
Figure 6. Startup Circuit with Large Capacitors on LED Strings
of the rectifier diode, external MOSFET, sense resis-
tor, and output capacitor to avoid excessive switching
noise. Use wide and short traces for the gate-drive
loop from the EXT pin, to the MOSFET gate, and
through the current-sense resistor, then returning to
the IC GND pin.
with short and wide connections. The high-current
input loop goes from the positive terminal of the input
capacitor to the inductor, to the external MOSFET,
then to the current-sense resistor, 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 rectifier diode, to
the positive terminal of the output capacitors,
reconnecting between the output capacitor 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.
input and output capacitor ground and negative ter-
minal of the current-sense resistor. Connect all
these together with short, wide traces or a small
Current Balancing for LCD Panel Applications
V
IN
SHDN
MAX8790
______________________________________________________________________________________
Six-String White LED Driver with Active
L1
EXT
FB2
FB3
FB4
FB5
FB6
FB1
PCB Layout Guidelines
N1
TO V
D1
C
OUT
IN
V
1MΩ
OUT
4) Place the overvoltage detection-divider resistors as
5) Place the IN pin bypass capacitor as close to the
6) Minimize the size of the LX node while keeping it
7) Refer to the MAX8790 evaluation kit for an example
ground plane. Maximizing the width of the power
ground traces improves efficiency and reduces out-
put-voltage ripple and noise spikes. Create an ana-
log ground island (AGND) consisting of the
overvoltage detection-divider ground connection,
the ISET and FSET resistor connections, CCV and
CPLL capacitor connections, and the device’s
exposed backside pad. Connect the AGND and
PGND islands by connecting the GND pins directly
to the exposed backside pad. Make no other con-
nections between these separate ground planes.
close to the OV pin as possible. The divider’s cen-
ter trace should be kept short. Placing the resistors
far away causes the sensing trace to become
antennas that can pick up switching noise. Avoid
running the sensing traces near LX.
device as possible. The ground connection of the
IN bypass capacitor should be connected directly
to GND pins with a wide trace.
wide and short. Keep the LX node away from the
feedback node and ground. If possible, avoid run-
ning the LX node from one side of the PCB to the
other. Use DC traces as shields, if necessary.
of proper board layout.
C
LED
21