MAX1574ETB+T Maxim Integrated Products, MAX1574ETB+T Datasheet - Page 6

• Manufacturer Part Number: MAX1574ETB+T
• Description: IC LED DRVR WHITE BCKLGT 10-TDFN
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LEDr

Specifications of MAX1574ETB+T

• Constant Current: Yes
• Topology: Linear (LDO), Switched Capacitor (Charge Pump)
• Number Of Outputs: 3
• Internal Driver: Yes
• Type - Primary: Backlight, Flash/Torch
• Type - Secondary: White LED
• Frequency: 1MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 5V
• Mounting Type: Surface Mount
• Package / Case: 10-TDFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 60mA
• Internal Switch(s): Yes
• Efficiency: 83%
• Number Of Segments: 3
• Low Level Output Current: 60 mA
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Supply Current: 2 mA
• Maximum Power Dissipation: 1454 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 MAX1574 charge pump drives up to three white
LEDs with regulated constant current for uniform inten-
sity. By utilizing adaptive 1x/2x charge-pump modes
and very-low-dropout current regulators, it achieves
180mA output drive capability and high efficiency over
the 1-cell lithium-battery input voltage range. Fixed-fre-
quency switching of 1MHz allows for tiny external com-
ponents, and the regulation scheme is optimized to
ensure low EMI and low input ripple.
When V
1x mode and V
rent regulators regulate the LED current. As V
V
130mV, and the MAX1574 starts switching in 2x mode.
When the input voltage rises above V
mately 50mV, the MAX1574 switches back to 1x mode.
The MAX1574 includes soft-start circuitry to limit 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 volt-
age approaches the input voltage. Once this occurs, the
charge pump determines if 1x or 2x mode is required. In
the case of 1x mode, the soft-start is terminated and nor-
mal operation begins. During the soft-start time, the out-
put current is set to 5% of the maximum set by R
the case of 2x mode, soft-start operates until the lowest of
LED1 to LED3 reaches regulation. If an overload condi-
tion occurs, soft-start repeats every 2.1ms. If the output is
shorted to ground, the output current is limited by the
MAX1574 switching technique.
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
Figure 1. EN Timing Diagram
6
LED_
EN
I
LED_
_______________________________________________________________________________________
eventually falls below the switchover threshold of
SHDN
IN
is higher than V
0
t
SOFT-START
OUT
INITIAL t
100%
≥ 50µs
is pulled up to V
HI
Detailed Description
OUT
1
90%
, the MAX1574 operates in
1x to 2x Switchover
2
80%
IN
3
. The internal cur-
70%
OUT
4
Soft-Start
60%
by approxi-
500ns TO 500µs
IN
5
50%
SET
drops,
t
LO
. In
The LED current at full brightness is set by a resistor,
R
When the LEDs are enabled by driving EN high, the
MAX1574 goes through soft-start, bringing the LED cur-
rent up to I
low (500ns to 500µs pulse width). Each pulse reduces
the LED current by 10%, so after one pulse the LED cur-
rent is 0.9 x I
5%, so the I
x I
I
If dimming control is not required, EN works as a simple
on/off control. Drive EN high to enable the LEDs, or
drive EN low for shutdown.
When EN is held low for 2ms or longer, the MAX1574
is shut down and put in a low-current mode. OUT is
internally pulled to GND with 5kΩ during shutdown.
If any LED fails as an open circuit, the output voltage is
limited to about 5V by gating on/off the charge pump.
If any LED_ is floating or grounded, the MAX1574 oper-
ates in the same overvoltage-protection mode. To avoid
overvoltage-protection mode when using fewer than
three LEDs, connect any unused LED_ to IN (Figure 3).
The MAX1574 includes a thermal-limit circuit that shuts
down the IC at approximately +160°C. The part turns on
after the IC cools by approximately 20°C.
LED_
SET
6
≥ 500ns
LED
t
40%
HI
, as follows:
. Figure 1 shows a timing diagram for EN.
. The eleventh pulse sets the LED current back to
7
30%
LED_
LED_
8
LED
20%
. Dimming is then done by pulsing EN
. The tenth pulse reduces the current by
9
current reduces from 0.1 x I
R
10%
SET
10
Setting the Output Current
=
5%
Overvoltage Protection
11
0 6
.
100% 90%
I
V
EN Dimming Control
LED
Thermal Shutdown
×
_
393
Shutdown Mode
2ms
t
SHDN
(typ)
LED_
SHDN
to 0.05