MAX1698EUB Maxim Integrated Products, MAX1698EUB Datasheet - Page 6

• Manufacturer Part Number: MAX1698EUB
• Description: IC LED DRVR WT/CLR BCKLGT 10MSOP
• Manufacturer: Maxim Integrated Products
• Type: Backlight, White LED, Color LEDr

Specifications of MAX1698EUB

• Topology: Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: Backlight
• Type - Secondary: White LED
• Voltage - Supply: 2.7 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Operating Temperature: -40°C ~ 85°C
• Internal Switch(s): Yes
• Efficiency: 90%
• Low Level Output Current: 200 mA
• High Level Output Current: 200 mA
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Power Dissipation: 444 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -
• Frequency: -
• Current - Output / Channel: -

High-Efficiency Step-Up
Current Regulator for LEDs
The MAX1698/MAX1698As' high efficiency and small
size make them ideally suited to drive LEDs. They oper-
ate as a boost DC-DC converter that controls output
current rather than voltage. Losses are minimized by a
low, 300mV current-sense threshold. In the standard
configuration, a feedback resistor, R
through the primary chain of LEDs. Additional chains of
matching LEDs can be added with an equivalent resis-
tor. In matched LED arrays, the secondary chain cur-
rents closely track the primary chain. An optional zener
diode, D2, prevents overvoltage in the event that one of
the LEDs in the primary chain becomes an open circuit.
The LED brightness can be adjusted dynamically by a
voltage input at ADJ.
In shutdown, the supply current is reduced below 1µA.
EXT goes low in shutdown, shutting off the external N-
channel FET. This leaves a current path between the
input and the LEDs through the boost inductor and
catch diode. The minimum forward voltage of the LED
array must exceed the maximum V
the LEDs remain off in shutdown. Typical shutdown tim-
ing characteristics are shown in the Typical Operating
Characteristics.
Figure 2. Typical Operating Circuit
6
_______________________________________________________________________________________
V
BATT
V
CC
= 3.3V
= 3.3V
1µF
Detailed Description
10µF
V
SHDN
REF
ADJ
CC
GND
MAX1698A
MAX1698
10µH
BATT
FB
, sets the current
PGND
to ensure that
Shutdown
EXT
CS
FB
OPTIONAL
MBR0540
DZ
The MAX1698/MAX1698A include a soft-start function
that eliminates input current surges at turn-on. They do
this by extending the external FET driver (EXT) mini-
mum off-time during start-up. During the first 512
switching cycles, the minimum off-time is 5µs. It is then
allowed to drop to 2µs for the next 1500 switching
cycles. After that time, the minimum off-time falls to the
1µs value used during normal operation. (See
Shutdown/Soft-Start Timing in the Typical Operating
Characteristics section.)
Resistor R
chain of LEDs:
where I
R
be reduced proportional to the voltage at the ADJ pin
(see Normalized Output Current vs. ADJ Voltage in the
Typical Operating Characteristics section). Figure 3
FB
R
FB
sets the maximum LED current. This current can
LEDMAX
15Ω
FB
Setting the Maximum LED Current
sets the maximum current in the primary
is the maximum LED current.
15Ω
R
FB
=
I
15Ω
LEDMAX
300
Adjusting LED Current
Design Procedure
mV
15Ω
LEDs
1µF
Soft-Start