MAX8790AETP+T Maxim Integrated Products, MAX8790AETP+T Datasheet - Page 10

• 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

The MAX8790A is a high-efficiency driver for arrays of
white LEDs. It contains a fixed-frequency, current-
mode, PWM step-up controller, 5V linear regulator, dim-
ming control circuit, and six regulated current sources
(see Figure 2). When enabled, the step-up controller
boosts the output voltage to provide sufficient head-
room for the current sources to regulate their respective
string currents. The MAX8790A features selectable
switching frequency (500kHz, 750kHz, or 1MHz), which
allows trade-offs between external component size and
operating efficiency. The control architecture automati-
cally skips pulses at light loads to improve efficiency
and prevents overcharging the output capacitor.
A PWM logic input signal, BRT, controls the LED bright-
ness. The MAX8790A supports both analog and digital
control of the LED current, and achieves 100:1 dimming
range. The MAX8790A’s dimming control circuit con-
sists of a PLL, a digital comparator, and a DAC. In direct
DPWM mode, the step-up controller and current source
Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
Figure 1. Typical Operating Circuit
10
511kΩ
1μF
______________________________________________________________________________________
7V TO 21V
V
IN
C
0.1μF
0.1μF
IN
1.2kΩ
N.C.
ENA
ISET
FSET
CCV
CPLL
EP
SHDN
V
BRT
OSC
CC
Detailed Description
0.1μF
MAX8790A
IN
4.7μH
L1
GND
EXT
FB2
FB3
FB4
FB5
FB6
FB1
CS
OV
N1
R
56mΩ
R2
37.4kΩ
S
are directly turned on and off by the PWM signal. In ana-
log dimming mode, an internal PLL, digital comparator,
and DAC circuit translate the PWM signal into an analog
signal that linearly controls the LED current, down to a
PWM duty factor of 12.5%.
The MAX8790A has multiple features to protect the
controller from fault conditions. Separate feedback
loops limit the output voltage if one or more LEDs fail
open or short. During operation, if one of the feedback
string voltages exceeds the V
tion threshold, the controller shuts down and latches off
after an internal timer expires. The controller features
cycle-by-cycle current limit to provide consistent opera-
tion and soft-start capability. A thermal-shutdown circuit
provides another level of protection.
The MAX8790A includes a 5V linear regulator that pro-
vides the internal bias and gate drive for the step-up
controller. When an external 5V is available, the internal
LDO can be overdriven to decrease power dissipation.
Otherwise, connect the IN pin to an input greater than
5.5V. The internal LDO is disabled when SHDN is low.
D1
C
1MΩ
OUT
R1
CC
UP TO 35V
V
to 0.6V (typ) protec-
OUT