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MAX8645X

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

INITIAL tHI

0

≥ 200μs

1

23

45

ENM1 AND ENM2

OR

ENF

tSOFT-START

32/32

IM_ OR IF_

SHUTDOWN

31/32

30/32

tLO

500ns TO 250μs

29/32 28/32 27/32

Figure 1. ENM_ and ENF Timing Diagram

Thermal Shutdown

The MAX8645X/MAX8645Y include a thermal-limit circuit

that shuts down the IC at approximately +160°C. Turn-

on occurs after the IC cools by approximately 20°C.

Applications Information

Setting the Main Output Current

SETM controls M1–M6 regulation current. Current flow-

ing into M1, M2, M3, M4, M5, and M6 is a multiple of

the current flowing out of SETM:

IM1 = IM2 = IM3 = IM4 = IM5 = IM6 = K x (0.6V / RSETM)

where K = 230, and RSETM is the resistor connected

between SETM and GND (see the Typical Operating

Circuit).

Table 1. ENM1/ENM2 States

ENM1/ENM2 STATES

BRIGHTNESS

M1–M6

CURRENT

ENM1 = low, ENM2 = low

Shutdown

ENM1 = high, ENM2 = high Full brightness

0

230 x ISETM

Setting the Flash Output Current

SETF controls the F1, F2 regulation current. Current

flowing into F1 and F2 is a multiple of the current flow-

ing out of SETF:

IF1 = IF2 = N x (0.6V / RSETF)

where N = 1380.

Single-Wire Pulse Dimming

For more dimming flexibility or to reduce the number of

control traces, the MAX8645X/MAX8645Y support serial

pulse dimming. Connect ENM1 and ENM2 together to

enable single-wire pulse dimming of the main LEDs (or

ENF only for single-wire pulse dimming of the flash

LEDs). See Figure 2. When ENM1 and ENM2 (or ENF)

go high simultaneously, the main (or flash) LEDs are

enabled at full brightness. Each subsequent low-going

pulse (500ns to 250µs pulse width) reduces the LED

27 28 29 30 31 32

tHI

≥ 500ns

tSHDN

32/32 31/32 2.5ms (typ)

5/32 4/32 3/32 2/32 1/32

SHUTDOWN

current by 3.125% (1/32), so after one pulse, the LED

current is 96.9% (or 31/32) x ILED. The 31st pulse

reduces the current to 0.03125 x ILED. The 32nd pulse

sets the LED current back to ILED. Figure 1 shows a

timing diagram for single-wire pulse dimming. Because

soft-start is longer than the initial tHI, apply dimming

pulses quickly upon startup (after initial tHI) to avoid

LED current transitioning through full brightness.

Simple On/Off Control

If dimming control is not required, connect ENM1 to

ENM2 for simple on/off control. Drive both ENM1 and

ENM2 to a logic-level high to turn on the main LEDs.

Drive both ENM1 and ENM2 to a logic-level low to turn

off the main LEDs. ENF is the simple on/off control for

the flash LEDs. Drive ENF to a logic-level high to turn

on the flash LEDs. Drive ENF to a logic-level low to turn

off the flash LEDs. In this case, LED current is set by

the values of RSETM and RSETF.

Driving Fewer than Eight LEDs

When driving fewer than eight LEDs, two connection

schemes can be used. The first scheme is shown in

Figure 3 where LED drivers are connected together.

This method allows increased current through the LED

and effectively allows total LED current to be ILED multi-

plied by the number of connected drivers. The second

method of connection is shown in Figure 4 where stan-

dard white LEDs are used and fewer than eight are

connected. This scheme does not alter current through

each LED but ensures that the unused LED driver is

properly disabled.

Input Ripple

For LED drivers, input ripple is more important than out-

put ripple. Input ripple is highly dependent on the

source supply’s impedance. Adding a lowpass filter to

the input further reduces input ripple. Alternately,

increasing CIN to 22µF cuts input ripple in half with only

a small increase in footprint. The 1x mode always has

very low input ripple.

10 ______________________________________________________________________________________

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