MAX8790AETP+T Maxim Integrated Products, MAX8790AETP+T Datasheet - Page 21

• Manufacturer Part Number: MAX8790AETP+T
• Description: IC LED DRVR WHITE BCKLGT 20-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LEDr

Specifications of MAX8790AETP+T

• 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: 27mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Efficiency: -
• Lead Free Status / Rohs Status: Details

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
4) Place the overvoltage detection-divider resistors as
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
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.
Current Balancing for LCD Panel Applications
______________________________________________________________________________________
Six-String White LED Driver with Active
PCB Layout Guidelines
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 MAX8790A evaluation kit for an exam-
TRANSISTOR COUNT: 12,042
PROCESS: BiCMOS
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.
ple of proper board layout.
TOP VIEW
CPLL
FSET
CCV
ISET
IN
16
17
18
19
20
4mm x 4mm THIN QFN
15
1
MAX8790AETP+
14
2
Pin Configuration
Chip Information
13
3
12
4
11
5
10 FB5
9
8
7
6
FB4
GND
FB3
FB2
21