MAX8645X/MAX8645Y
1x/1.5x/2x White LED Charge Pumps with Two
LDOs in 4mm x 4mm TQFN
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Detailed Description
The MAX8645X/MAX8645Y charge pumps drive up to
six white LEDs in the main display for backlighting and
up to two white LEDs for flash, all with regulated con-
stant current for uniform intensity. By utilizing adaptive
1x/1.5x/2x charge-pump modes and very-low-dropout
current regulators, they achieve high efficiency over the
1-cell lithium-battery input voltage range. 1MHz fixed-
frequency switching allows for tiny external compo-
nents and low input ripple. Two on-board 200mA
programmable-output-voltage LDOs are provided to
meet camera-module requirements.
1x to 1.5x Switchover
When V
IN
is higher than V
OUT
, the MAX8645X/
MAX8645Y operate in 1x mode and V
OUT
is pulled up
to V
IN
. The internal current regulators regulate the LED
current. As V
IN
drops, V
M_
(or V
F_
) eventually falls
below the switchover threshold of 100mV and the
MAX8645X/MAX8645Y start switching in 1.5x mode.
When the input voltage rises above V
OUT
by approxi-
mately 50mV, the MAX8645X/MAX8645Y switch back to
1x mode.
1.5x to 2x Switchover
When V
IN
is less than V
OUT
but greater than 2/3 V
OUT
,
the MAX8645X/MAX8645Y operate in 1.5x mode. The
internal current regulators regulate the LED current. As
V
IN
drops, V
M_
(or V
F_
) eventually falls below the
switchover threshold of 100mV, and the MAX8645X/
MAX8645Y start switching in 2x mode. When the input
voltage rises above 2/3 V
OUT
by approximately 50mV,
the MAX8645X/MAX8645Y switch back to 1.5x mode.
Soft-Start
The MAX8645X/MAX8645Y include soft-start circuitry to
limit inrush current at turn-on. Once the input voltage is
applied, the output capacitor is charged directly from
the input with a ramped current source (with no charge-
pump action) until the output voltage approaches the
input voltage. Once the output capacitor is charged,
the charge pump determines if 1x, 1.5x, or 2x mode is
required. In the case of 1x mode, the soft-start is termi-
nated and normal operation begins. In the case of 1.5x
or 2x mode, soft-start operates until the lowest voltage
of M1–M6 and F1, F2 reaches regulation. If the output
is shorted to ground or is pulled to less than 1.25V, the
output current is limited by soft-start.
True Shutdown™ Mode
When ENM1, ENM2, and ENF are simultaneously held
low for 2.5ms or longer, the MAX8645X/MAX8645Y are
shut down and put in a low-current shutdown mode,
and the input is isolated from the output. OUT is inter-
nally pulled to GND with 5kΩ during shutdown.
Thermal Derating
The MAX8645X/MAX8645Y limit the maximum LED cur-
rent depending on the die temperature. The maximum
LED current is set by the R
SETM
and R
SETF
resistors.
Once the temperature reaches +40°C, the LED current
decreases by 1.7%/°C. Due to the package’s exposed
paddle, the die temperature is always very close to the
PCB temperature.
The temperature derating function allows the LED cur-
rent to be safely set higher at normal operating temper-
atures, thereby allowing either a brighter display or
fewer LEDs to be used for normal display brightness.
Pin Description (continued)
Transfer Capacitor 1 Positive Connection. Connect a 1µF ceramic capacitor between C1P and C1N.
During shutdown, if OUT > IN, C1P is shorted to OUT. If OUT < IN, C1P is shorted to IN.
Charge-Pump Output. Bypass OUT to GND with a 10µF ceramic capacitor. Connect to the anodes of
all the LEDs. OUT is internally pulled to ground through a 5kΩ resistor during
Transfer Capacitor 2 Positive Connection. Connect a 1µF ceramic capacitor between C2P and C2N.
During shutdown, if OUT > IN, C2P is shorted to OUT. If OUT < IN, C2P is shorted to IN.
Transfer Capacitor 2 Negative Connection. Connect a 1µF ceramic capacitor between C2P and C2N.
C2N is internally shorted to IN during shutdown.
Default Output-Voltage Select Input. P1 and P2 set the LDO1 and LDO2 voltages to one of nine
combinations (Table 2). P1 is high impedance in an off condition and shortly after in an on condition.
