MAX8645X(2006) 查看數據表（PDF） - Maxim Integrated

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MAX8645X
(Rev.:2006)

1x/1.5x/2x White LED Charge Pumps with Two LDOs in 4mm x 4mm TQFN

Maxim Integrated 

1x/1.5x/2x White LED Charge Pumps with Two

LDOs in 4mm x 4mm TQFN

Pin Description (continued)

PIN

NAME

FUNCTION

23

C1P

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.

24

PGND Power Ground. Connect PGND to system ground. PGND is used for charge-pump switching currents.

25

OUT

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 shutdown.

26

C2P

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.

27

C2N

Transfer Capacitor 2 Negative Connection. Connect a 1µF ceramic capacitor between C2P and C2N.

C2N is internally shorted to IN during shutdown.

28

P1

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.

—

EP

Exposed Paddle. Connect to GND and PGND.

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 VIN is higher than VOUT, the MAX8645X/

MAX8645Y operate in 1x mode and VOUT is pulled up

to VIN. The internal current regulators regulate the LED

current. As VIN drops, VM_ (or VF_) eventually falls

below the switchover threshold of 100mV and the

MAX8645X/MAX8645Y start switching in 1.5x mode.

When the input voltage rises above VOUT by approxi-

mately 50mV, the MAX8645X/MAX8645Y switch back to

1x mode.

1.5x to 2x Switchover

When VIN is less than VOUT but greater than 2/3 VOUT,

the MAX8645X/MAX8645Y operate in 1.5x mode. The

internal current regulators regulate the LED current. As

VIN drops, VM_ (or VF_) 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 VOUT by approximately 50mV,

the MAX8645X/MAX8645Y switch back to 1.5x mode.

True Shutdown is a trademark of Maxim Integrated Products, Inc.

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 2ms 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 RSETM and RSETF 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.

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