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MAX8930
WLED Charge Pump, RGB, OLED Boost,
LDOs with ALC and CAI
Detailed Description
The MAX8930 integrates a negative charge pump for
both white LED display backlighting with ambient light
control (ALC) function, content adaptive interface (CAI)
function, and R/G/B LED. There is one step-up converter
for passive matrix OLED (PMOLED) oriented application
and three LDOs with programmable output voltage. The
three LDO outputs are able to convert to GPO (general-
purpose output) status through an I 2 C command. The
MAX8930 includes soft-start, thermal shutdown, open-
circuit, and short-circuit protection in the charge-pump
circuitry.
Reset Control
The MAX8930 uses two different methods of reset: soft-
ware and hardware.
Software Reset: All the registers are initiated by RESET
= 1 at Register 00h. After that, the values in all registers
come back to POR (power-on-reset) state. The bit of
RESET in 00h is automatically returned to 0. Auto return
to 0.
LED Charge Pump
The charge pump drives up to 8 white LEDs (4 WLEDs
for main and 4 WLEDs for sub) and 3 RGB LEDs with
regulated constant current for both display backlight and
fun light applications. By utilizing individually adaptive
1x/-0.5x negative charge-pump modes and extremely
low-dropout current regulators, it is able to achieve high
efficiency over the full 1-cell lithium battery input volt-
age range. High-frequency switching of 4MHz allows
for tiny external components. The regulation scheme is
optimized to ensure low EMI and low input ripple. Each
channel for WLED and RGB LED has the capability of
delivering 25.6mA with 256 dimming steps (0.1mA per
step). The current-level adjustment is programmed by
an I 2 C command. Figure 2 is the flow chart of the startup
and mode-change algorithm.
SHUTDOWN
V NEG DISCHARGED
BY RESISTOR
Hardware Reset: Hardware reset is done by toggling EN
from logic-high to logic-low. All the registers under hard-
ware reset conditions are returned to their initial values
(POR) and stop receiving any commands.
Open-Circuit and Short-Circuit Protection
If any WLED/RGB fails as an open circuit, that LED pin
pulls to ground, and the IC is forced into -0.5X mode.
Therefore, connect any unused WLED_/RGB pins to PV1,
PV2, or PV3 to disable the corresponding current regu-
lator. The MAX8930 contains special circuitry to detect
RESET = 1 OR EN = 0 OR
MAIN WLED = 0 AND
WLED5?8 = 0 AND
RI2C, GI2C, BI2C = 0
EN = HIGH, RESET = 0 AND
MAINI2C = 1,
MAIN WLED = 1 OR
WLED5?8 = 1 OR
RI2C, GI2C, BI2C = 1
PUMP OFF
PUMP OFF
ALL WLED_ AND
RGB IN 1x MODE
ANY V LED < 150mV
this condition and disables the corresponding current
regulator to avoid wasting battery current.
Thermal Shutdown
The MAX8930 includes a thermal-limit circuit that shuts
down the IC at about +160 N C. The part turns on after the
IC cools by approximately 20 N C.
Thermal shutdown is applied to the following blocks:
? White and RGB LED driver
? Step-up converter
? LDO1, LDO2, LDO3
PUMP SOFT-START
PUMP GATE-DRIVE RAMPED
ALL WLED_ AND RGB IN
1x MODE
PUMP SOFT-START DONE
(0.5ms TYP)
PUMP ON
PUMP ON
EACH WLED_ AND RGB IN 1x
OR -0.5x MODE AS NEEDED
ALL V LED > 250mV
? SBIAS
22
Figure 2. Startup and Mode Change Algorithm
Maxim Integrated
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