ia2505 integration, ia2505 Datasheet - Page 5

• Manufacturer Part Number: ia2505
• Description: Ia2505 Four Channel Led Current Source For Flash And Backlighting
• Manufacturer: integration

DETAILED DESCRIPTION
The IA2505 is a high-efficiency, low-cost, high-current, four
channel LED current source specifically designed for running
flash and backlighting LEDs. LED current can be set from 5mA
to 80mA on each channel, and the individual LED currents are
matched to within +/-10%. LED pulse current can be as high
as 200mA for duration of 20msec or less. Dropout voltage is
only 30mV at 20mA, permitting direct operation from a Li-Ion
battery. The IA2505 can also be operated from two or three
Alkaline batteries or a Lithium battery cell. The only external
component required is a resistor that sets the current. The
IA2505 is available in an MSOP-8 and a space-saving 3mm x
3mm DFN package.
Startup
When the IA2505 EN pin is pulled high, the four outputs begin
pulling the correct current within 600µsec. No soft-start
capacitor is required.
Backlight Operation
The IA2505 can be used for backlight operation with four
channels in parallel. The current is set by the resistor
connected from the I
proportional to the resistor value according to the formula
I
where I
applied to the anodes of the LEDs decreases, the current
through the LEDs will remain constant, until there is insufficient
voltage to forward bias the LEDs at that current. This occurs
when the voltage on the LED pin of the IA2505 reaches
approximately 30mV. For best operation, the battery voltage
should be at least 30mV higher than the maximum LED forward
bias voltage.
Flash-Mode Operation
The IA2505 is suitable for running one to two standard LEDs
for use in a camera flash, or for running a high-power LED for
the same purpose. To run two LEDs for flash, the current may
be set to 200mA/LED by selecting a 5.6KΩ SET resistor, and
then running the EN from the shutter signal. The flash duration
should be 20msec or less.
Characteristics, turn-on time is < 600µsec, and turn-off is
about 10µsec
The 1W LEDs in this configuration can also be run as a
flashlight (torch) by attaching another resistor to the SET pin
through a switch. The designer need only be careful to avoid
excessive power dissipation in the IC.
out
= α / R
out
set
is the current in each single LED. As the voltage
= 1200 / R
set
pin, the output current being inversely
set
,
As shown in the Typical
Input and Output Capacitors
Since the IA2505 has no switching, input capacitor is optional
for this circuit. However, if the LED current is intended to be
modulated, for example by Pulse Width Modulating the EN pin
for dimming, or for camera flash, an input capacitor of 100nF
value is recommended.
capacitor (MLCC) is recommended.
inexpensive and have very low equivalent series resistance
(ESR, ≤15mΩ). Table 1, Ceramic Capacitor Manufacturers lists
suggested capacitor suppliers for the typical application circuit
EMI
Since the IA2505 doesn't switch, it generates no noise,
eliminating troublesome electromagnetic interference (EMI).
Enable
The IA2505 can be turned off by pulling the EN pin low. It has
an active-high EN pin (LOW = shutdown, HIGH = ON). In the
shutdown condition, there is extremely low leakage current into
the IC, and very low current into the LEDs. The IA2505 typically
draws only 40µA when operating in the no-load condition and
draws less than 0.01µA when the device is shutdown.
PWM Brightness Control
The brightness of the LEDs can be varied from zero up to the
maximum programmed current level by applying a Pulse Width
Modulated (PWM) signal to the EN pin of the IA2505. LED
brightness is proportional to the duty cycle of the PWM signal.
PWM frequency greater than 100Hz is recommended to avoid
flickering of the LED light. For the IA2505, zero duty cycle will
turn off the LEDs and a 50% duty cycle will result in an average
output current being half of the programmed LED current.
Thermal Shutdown
If the IA2505 junction temperature reaches 160°C, the IC will
automatically shutdown. Once the junction temperature cools
down by 10°C, the device will turn on.
Manufacturer
Taiyo Yuden
Table 1: Ceramic Capacitor Manufacturers
Murata
TDK
A surface-mount multi-layer ceramic
www.component.tdk.com
www.t-yuden.com
www.murata.com
Contact
MLCCs are small,
IA2505
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