MAX8645YETI+T Maxim Integrated Products, MAX8645YETI+T Datasheet - Page 10

• Manufacturer Part Number: MAX8645YETI+T
• Description: IC LED DRVR WHITE BCKLGT 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LEDr

Specifications of MAX8645YETI+T

• Constant Current: Yes
• Topology: Linear (LDO), Switched Capacitor (Charge Pump)
• Number Of Outputs: 8
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 1MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 5.5V
• Mounting Type: Surface Mount
• Package / Case: 28-TQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 200mA
• Internal Switch(s): Yes
• Efficiency: 85%
• Number Of Segments: 8
• Low Level Output Current: 400 mA
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Supply Current: 5.5 mA
• Maximum Power Dissipation: 1666 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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.
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:
where K = 230, and R
between SETM and GND (see the Typical Operating
Circuit ).
SETF controls the F1, F2 regulation current. Current
flowing into F1 and F2 is a multiple of the current flow-
ing out of SETF:
where N = 1380.
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
1x/1.5x/2x White LED Charge Pumps with Two
LDOs in 4mm x 4mm TQFN
Figure 1. ENM_ and ENF Timing Diagram
Table 1. ENM1/ENM2 States
10
I
ENM1 = low, ENM2 = low
ENM1 = high, ENM2 = high
M1
ENM1/ENM2 STATES
= I
______________________________________________________________________________________
ENM1 AND ENM2
M2
ENF
OR
I
M_
= I
OR I
SHUTDOWN
M3
F_
Setting the Flash Output Current
I
F1
Setting the Main Output Current
Applications Information
= I
= I
0
M4
F2
t
SOFT-START
Single-Wire Pulse Dimming
= N x (0.6V / R
= I
INITIAL t
≥ 200μs
32/32
SETM
M5
BRIGHTNESS
Full brightness
HI
= I
Shutdown
is the resistor connected
Thermal Shutdown
M6
1
= K x (0.6V / R
31/32
SETF
2
30/32
)
3
230 x I
29/32
CURRENT
M1–M6
500ns TO 250μs
4
0
28/32
SETM
SETM
5
27/32
)
t
LO
current by 3.125% (1/32), so after one pulse, the LED
current is 96.9% (or 31/32) x I
reduces the current to 0.03125 x I
sets the LED current back to I
timing diagram for single-wire pulse dimming. Because
soft-start is longer than the initial t
pulses quickly upon startup (after initial t
LED current transitioning through full brightness.
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
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 I
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.
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
a small increase in footprint. The 1x mode always has
very low input ripple.
≥ 500ns
27
t
5/32
HI
28
4/32
IN
29
3/32
SETM
to 22µF cuts input ripple in half with only
Driving Fewer than Eight LEDs
30
2/32
and R
31
1/32
SETF
32
Simple On/Off Control
32/32
.
LED
31/32
LED
LED
. Figure 1 shows a
HI
2.5ms (typ)
. The 31st pulse
t
. The 32nd pulse
SHDN
, apply dimming
Input Ripple
HI
SHUTDOWN
) to avoid
LED
multi-