MAX8631_08 Datasheet, PDF (11/15 Pages) Maxim Integrated Products – 1x/1.5x/2x White LED Charge Pump with Two LDOs in 4mm x 4mm Thin QFN

1x/1.5x/2x White LED Charge Pump with Two
LDOs in 4mm x 4mm Thin QFN
INITIAL t_HI
0
≥ 200μs
1
23
45
ENM1 AND ENM2
OR
ENF
t_SOFT-START
32/32
I_{M_} OR I_{F_}
SHUTDOWN
31/32
30/32
t_LO
500ns TO 250μs
29/32 _{28/32 27/32}
Figure 2. ENM_ and ENF Timing Diagram
Thermal Shutdown
The MAX8631X/Y includes 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–M4 regulation current. Current flow-
ing into M1, M2, M3, and M4 is a multiple of the current
flowing out of SETM:
I_M1 = I_M2 = I_M3 = I_M4 = K x (0.6V / R_SETM)
where K = 230, and R_SETM is the resistor connected
between SETM and GND (see the Typical Operating
Circuit).
Table 1. ENM1/ENM2 States
ENM1/ENM2 STATES BRIGHTNESS
ENM1 = low, ENM2 = low
Shutdown
ENM1 = high, ENM2 = high Full brightness
M1–M4
CURRENT
0
230 x I_SETM
Setting the Flash Output Current
SETF controls the F1–F4 regulation current. Current
flowing into F1, F2, F3, and F4 is a multiple of the cur-
rent flowing out of SETF.
I_F1 = I_F2 = I_F3 = I_F4 = N x (0.6V / R_SETF)
where N = 690.
Single-Wire Pulse Dimming
For more dimming flexibility or to reduce the number of
control traces, the MAX8631X/Y supports 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 3. When ENM1 and ENM2 (or ENF) go high
simultaneously, the main (or flash) LEDs are enabled at
full brightness. Each subsequent low-going pulse
27 28 29 30 31 32
t_HI
≥500ns
32/32 _31/32
t_SHDN
(2.5ms)
5/32 _{4/32 3/32 2/32 1/32}
SHUTDOWN
(500ns to 250µs pulse width) reduces the LED current
by 3.125% (1/32), so after one pulse the LED current is
96.9% (or 31/32) x I_LED. The 31st pulse reduces the
current to 0.03125 x I_LED. The 32nd pulse sets the LED
current back to I_LED. Figure 2 shows a timing diagram
for single-wire pulse dimming. Because soft-start is
longer than the initial t_HI, apply dimming pulses quickly
upon startup (after initial t_HI) to avoid LED current tran-
sitioning 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 R_SETM and R_SETF.
Driving Fewer than 8 LEDs
When driving fewer than 8 LEDs, two different connec-
tion schemes can be used. The first scheme is shown
in Figure 4 where LED drivers are connected together.
This method allows increased current through the LED
and effectively allows total LED current to be I_LED multi-
plied by the number of connected drivers. The second
method of connection is shown in Figure 5 where stan-
dard white LEDs are used and fewer than 8 are con-
nected. 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 C_IN to 22µF cuts input ripple in half with only
a small increase in footprint. The 1x mode always has
very low input ripple.
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