MAX8790AETP+T Maxim Integrated Products, MAX8790AETP+T Datasheet - Page 15

• 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

Table 2. Dimming Mode
In digital dimming mode, the step-up controller and
current source are directly turned on and off by the
PWM signal. The current pulse magnitude, or full-scale
current, is set by ISET and is independent of PWM duty
factor. The current-source outputs are PWM signals
synchronized to the BRT input signal (see Figure 5).
The full-scale current in both methods is specified by
resistance from the ISET pin to ground:
The acceptable resistance range is 74kΩ < R
133kΩ, which corresponds to full-scale LED current of
27mA > I
default full-scale LED current of 20mA. When ENA is
high, the analog dimming is enabled, when ENA is low,
digital dimming is enabled.
When the current-source output is pulse-width modulated,
current-source turn-on is synchronized with the BRT
signal. Synchronization and low jitter in the PWM sig-
nals help reduce flicker noise in the display. The cur-
rent through each FB_ pin is controlled only during the
Figure 5. LED Current Control Using DPWM Dimming Mode
Analog + DPWM
Direct DPWM
D =
I
I
0A
BRT
LEDMAX
LED
Current Balancing for LCD Panel Applications
MODE
t
t
BRT
ON
LEDmax
D = 50%
t
t
ON
BRT
I
LED
> 15mA. Connect ISET to V
> 2.1V
< 0.8V
______________________________________________________________________________________
ENA
max
Six-String White LED Driver with Active
=
20
250kΩ < R
mA
V
PLL FREQUENCY
FSET
R
disables PLL
ISET
×
100 Ω
> V
FSET
CC
k
D = 30%
- 0.4V,
< 754kΩ
CC
ISET
OPEN
DPWM DIMMING MODE
CPLL
0.1µF
for a
<
Analog dimming from 100% to 12.5% brightness. From 12.5% to
1% brightness, DPWM dimming is employed. BRT frequency
range is 100Hz to 500Hz.
Direct dimming by BRT signal. BRT frequency can be 100Hz to
2kHz; 50µs minimum BRT on-time limits the minimum brightness.
step-up converter’s on-time. During the converter’s off-
time, the current sources are turned off. The output volt-
age does not discharge and stays high. Each FB_ pin can
withstand 28V, which is the pin’s maximum rated voltage.
Table 2 summarizes the characteristics of both analog
and digital dimming methods.
A PLL translates the duty cycle of the BRT input into a
reference for the MAX8790A’s current sources. A resis-
tor from the FSET pin to ground controls the PLL’s free-
running frequency:
The PLL’s loop filter bandwidth is set with a capacitor
from the CPLL pin to ground. This filter integrates the
phase difference between the BRT input signal and the
PLL oscillator. The filter bandwidth determines the
PLL’s dynamic response to frequency changes in the
BRT signal. For most applications, a 0.1µF capacitor is
adequate for oscillator frequencies in the 166Hz < f
< 500Hz range. The PLL frequency capture window is
0.6 x f
D = 12.5%
PLL
to f
PLL
f
PLL
.
DESCRIPTION
=
10
×
R
FSET
1
×
800
D = 6.25%
pF
PLL
15