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MAX8630X

125mA 1x/1.5x Charge Pumps for 5 White LEDs in 3mm x 3mm TDFN

Maxim Integrated 

125mA 1x/1.5x Charge Pumps for 5 White LEDs

in 3mm x 3mm TDFN

Detailed Description

The MAX8630_ charge pump drives up to 5 white LEDs

(3 main LEDs and 2 sub LEDs) with regulated constant

current for uniform intensity. By utilizing adaptive 1x/1.5x

charge-pump modes and very low-dropout current regu-

lators, it achieves 125mA guaranteed output-drive capa-

bility and high efficiency over the 1-cell Li+ battery input

voltage range. 1MHz fixed-frequency switching allows

for tiny external components and the regulation scheme

is optimized to ensure low EMI and low input ripple. The

MAX8630X provides independent on/off/dimming control

for main and sub displays (see Figure 1). The

MAX8630W allows direct-PWM dimming of all five LEDs

together (see Figure 2). A functional diagram for the

MAX8630X/MAX8630W is shown in Figure 3.

1x to 1.5x Switchover

When VIN is higher than VOUT, the MAX8630_ operates

in 1x mode and VOUT is pulled up to VIN. The internal

current regulators regulate the LED current. As VIN

drops, VLEDMIN_ eventually falls below the switchover

threshold of 88mV, and the MAX8630_ starts switching

in 1.5x mode, and VLEDMIN is regulated to 122mV by

the charge pump. To switch back to 1x mode, the

MAX8630_ determines if VIN - VOUT is sufficient to keep

VLEDMIN greater than 88mV. The comparator that

makes this judgment is adaptive and matches the

switchover for the conditions.

Soft-Start

The MAX8630_ includes soft-start circuitry to eliminate

inrush current at turn-on. 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 approaches the input voltage.

Once this occurs, the charge pump enters 1x mode,

and the LED output current is then ramped up in 32 lin-

ear steps. If the current regulators are in dropout at the

end of this time, the charge pump switches to 1.5x

mode. If the output is shorted to ground (VOUT <

1.25V), the part stays in the initial soft-start stage and

output current is limited by the ramped current source.

Additionally, when the main or sub LED current rolls

over from 1/32 to full, the LED current regulators soft-

start again to eliminate input current spikes.

ENM/ENS Dimming Control (MAX8630X)

When the LEDs are enabled (by driving EN_ high), the

MAX8630X goes through soft-start and brings the LED

current up in 32 linear steps. Dim the MAX8630X by puls-

ing EN_ low (500ns to 500µs pulse width). Each pulse

reduces the LED current by 1/32nd. After 31 pulses, the

current reaches 1/32, and the next pulse restores the cur-

rent to 100%. Figure 4 shows a timing diagram for EN_.

If dimming control is not required, ENM and ENS work

as simple on/off controls. Drive ENM/ENS high to

enable the LEDs, or drive ENM/ENS low for shutdown.

The LEDs operate at 100% brightness under these sim-

ple on/off conditions.

PWM Dimming Control (MAX8630W)

Dim the MAX8630W by applying a direct-PWM logic-

level signal to PWM. An internal resistor combined with

the capacitor at CPWM forms a lowpass filter that con-

verts the PWM signal to DC LED current that is propor-

tional to the PWM signal’s duty cycle. All five LEDS are

controlled together on the MAX8630W. The PWM fre-

quency range is 900Hz to 200kHz.

If dimming control is not required, PWM works as a sim-

ple on/off control. Drive PWM high to enable the LEDs,

or drive PWM low for shutdown.

0

EN_

ILED_

SHUTDOWN

INITIAL tHI

> 50μs

1

2

3

4

5

tSOFT-START

FULL

tLO

31/32

30/32

29/325002n8s/3T2O

500μs

27/32

Figure 4. MAX8630X EN_ Timing Diagram

27 28 29 30 31 32

tHI

>500ns

FULL 31/32

tSHDN

4ms

6/32 5/32 4/32 3/32 2/32 1/32

SHUTDOWN

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