MAX1707 Maxim Integrated Products, MAX1707 Datasheet - Page 9

• Manufacturer Part Number: MAX1707
• Description: Light-Management IC
• Manufacturer: Maxim Integrated Products

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Table 1. Control Data Byte
The MAX1707 charge pump operates in three modes to
maintain high efficiency over a wide supply voltage
range. The IC automatically selects between these
three modes as described in the 1x/1.5x/2x Mode
Switchover section.
Current-sinking LED cathode connections are provided
to drive four main (M_) and three sub (S_) LEDs at a
regulated current up to 30mA each. The sub LED con-
nections can be used for either subdisplay backlighting
or one RGB indicator. The IC also contains four flash
LED connections (F_) that sink up to 100mA each.
These LED connections can be connected together in
any combination to provide increased current up to
610mA total.
An I
the LED currents in 32 linear steps. When using the
RGB indicator, the I
programmable ramp-up/down rates. The camera flash
can be turned on/off by the I
tal logic input with either method programmed to its
own brightness level.
When the input voltage is higher than the required out-
put voltage needed to drive the LEDs, the MAX1707
pulls OUT up to the input voltage (in 1x mode), while
still regulating the LED current with the current regula-
tors. As the input voltage drops, the lowest LED cath-
ode voltage falls below the 100mV switchover
threshold, and the MAX1707 starts switching in 1.5x
mode. When the input voltage is rising, the transition
from 1.5x to 1x is made when V
Note: C2 is MSB and D0 is LSB. X = Don’t care.
Strobe Brightness
Sub1 Brightness
Sub2 Brightness
Sub3 Brightness
Flash Brightness
Main Brightness
Other Functions
Light-Management IC with Efficient 1x/1.5x/2x
2
On/Off Control
C serial port is used for on/off control and setting
FUNCTION
Charge Pump for Backlight/Flash/RGB LEDs
_______________________________________________________________________________________
1x/1.5x/2x Mode Switchover
2
C port provides 32k colors and
Detailed Description
C2
0
0
0
0
1
1
1
1
2
C port or a separate digi-
IN
COMMAND
is greater than V
C1
0
0
1
1
0
0
1
1
C0
0
1
0
1
0
1
0
1
OUT
.
SDA CONTROL BYTE
Main
When the MAX1707 is running in 1.5x mode and the
input voltage is decreased, the lowest LED cathode
voltage crosses the 100mV switchover threshold again.
At this point, the MAX1707 changes to the 2x charge-
pump mode. With the input voltage rising and the
MAX1707 in 2x mode, the IC changes to 1.5x mode
once V
The MAX1707 includes soft-start circuitry to limit inrush
current at turn-on and mode transitions. When starting
up, the output capacitor is charged directly from the
input with a ramped current source (with no charge-
pump action) until the output voltage is near the input
voltage. After 512µs, if all the LED cathodes are not
above 100mV, the MAX1707 switches to 1.5x mode
with the LED output current ramped from 1/32 to the
programmed current in 1/32 steps. After another 512µs,
if all the LED cathodes are not above 100mV, the
MAX1707 switches to 2x mode, once again ramping
the LED current from 1/32 to the programmed current in
1/32 steps. Any time the output voltage is less than
1.25V, the soft-start routine is reset to the 1x state. Thus,
the startup time is 512µs, 1024µs, or 1536µs, depending
on what mode is required after the completion of startup.
The output currents for the main, sub, and flash current
regulators are set using the I
I
LEDs is always equal and set with a single command.
The currents for the three sub LEDs are set indepen-
dently, allowing them to drive an RGB LED. The cur-
rent-level settings for both the main and sub LEDs
range from 0.9mA to 30mA, defaulting to 15mA each
(see Tables 1, 2, and 3).
D4
2
X
C Interface section). The current for the four main
IN
32 steps, 100mA/LED max, STB enable
32 steps, 100mA/LED max, I
is greater than 2/3 of the output voltage.
Sub3
D3
X
32 steps, 30mA/LED max
32 steps, 30mA max
32 steps, 30mA max
32 steps, 30mA max
Derate
DATA
Temp
Sub2
D2
Output-Current Settings
2
C serial interface (see the
2
C enable
Sub1
D1
RGB Ramp Rate
Soft-Start
Flash
D0
9