MAX8822ETE+ Maxim Integrated Products, MAX8822ETE+ Datasheet - Page 10

• Manufacturer Part Number: MAX8822ETE+
• Description: IC LED DRVR WHITE BCKLGT 16-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LEDr

Specifications of MAX8822ETE+

• Constant Current: Yes
• Topology: Linear (LDO), PWM, Switched Capacitor (Charge Pump)
• Number Of Outputs: 4
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 1MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 5V
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 24mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Efficiency: -
• Lead Free Status / Rohs Status: Details

Ultra-Efficient Negative Charge-Pump LED
Driver with Dual LDOs in 3mm x 3mm Thin QFN
The LED current and LDO output voltages are pro-
grammed using a serial-pulse control interface. Pulse
ENLED low (as discussed in the LED Dimming Control
section) to decrease the LED current from 24mA to
0.1mA, or hold ENLED low for at least 2.5ms to place the
LED current regulators in shutdown mode. LED dimming
is controlled in 31 pseudo-logarithmic steps. Pulse
ENLDO low (as discussed in the LDO1/LDO2 Output
Voltage Control section) to choose LDO1 and LDO2 out-
put voltages from one of 16 combinations including off.
Drive both ENLED and ENLDO low for at least 2.5ms to
place the IC in low-power (0.5µA typ) shutdown mode.
The MAX8822 includes soft-start, thermal shutdown, and
open- and short-circuit protection.
When V
plus the 150mV (typ) dropout voltage of the current
regulator, the LED current returns through GND (Figure
4). If this condition is satisfied for all four WLEDs, the
charge pump remains inactive. When V
that the current regulator voltage (V
maintained above the dropout voltage for any of the
individual LEDs, the charge pump activates and gener-
ates a voltage on NEG that is no greater than 5V (typ)
below V
the switchover threshold voltage of 150mV (typ, V
falling), internal circuitry switches that current regula-
tor’s return path from GND to NEG to provide enough
voltage across that regulator to overcome dropout
(Figure 5). When V
of that current regulator is switched back from NEG to
GND. Each current regulator is independently moni-
tored to detect when switchover is required. Since the
LED current is switched for only the individual LED cur-
rent regulators requiring higher voltage, power con-
sumption is minimized.
Figure 4. Current Regulator Returning to GND
10
______________________________________________________________________________________
Adaptive Current Regulator Switchover
IN
IN
CONTROL
CURRENT
. For any current regulator that is detected at
LED
is higher than the forward voltage of an LED
REGULATOR
LED_
CURRENT
rises to 250mV (typ), the return
MAX8822
NEG
LED_
V
LED_
LED_
IN
V
> SWITCHOVER
IN
) cannot be
THRESHOLD
drops such
I
LED_
IN
The MAX8822 uses a serial-pulse control interface to
program the intensity of the LEDs. The dimming range
is pseudo-logarithmic from 24mA to 0.1mA in 31 steps.
All active LED current regulators are programmed to
the same value, with a 1% (typ) current accuracy and
0.3% current matching between regulators. To program
the LED current, pulse ENLED (500ns to 500µs pulse
width), as shown in Figure 1. An internal register accu-
mulates the pulse count on the rising edge of the
ENLED pulse. See Table 1 for the LED current values
and the corresponding ENLED pulse count. Once the
desired pulse count is met, hold ENLED high for at
least 2.5ms (t
value and enable the LED_ current at the programmed
level. If ENLED is pulsed more than 31 times before
latching, the pulse count restarts at 1 on the 32
edge. To program a new LED current level, follow the
previous sequence from the beginning. Drive ENLED
low for greater than 2.5ms (typ) to place the LED cur-
rent regulators in shutdown. When the MAX8822 starts
up with ENLED high, the LEDs turn on at full brightness.
If dimming control is not required, ENLED works as a
simple on/off logic control. Drive ENLED high for at
least 2.5ms to enable the LED current regulators, or
drive ENLED low for at least 2.5ms for shutdown. The
LED drivers operate at 100% brightness and off under
these conditions.
Figure 5. Current Regulator Returning to NEG
CONTROL
CURRENT
LED
HOLD
REGULATOR
CURRENT
) to internally latch the pulse-count
MAX8822
LED Dimming Control
NEG
LED_
V
LED_
< SWITCHOVER
V
IN
THRESHOLD
I
LED_
nd
rising