ia2521 integration, ia2521 Datasheet - Page 5

• Manufacturer Part Number: ia2521
• Description: Ia2521 Camera Flash Led Driver
• Manufacturer: integration

I
DETAILED DESCRIPTION
The IA2521 device is a low-cost integrated synchronous buck-
boost converter IC specifically designed for driving camera
flash LEDs, both for flash and for flashlight (torch) operation. It
can be operated from a single lithium cell or two alkaline cells,
and drives a single LED with high efficiency at up to 2W of
continuous power, with pulses up to 4W. The IA2521 device
has its torch-mode output current controlled by a resistor to
ground, flash-mode current controlled by a resistor to logic, and
pulse time controlled by an ENABLE signal. Full flash brightness
is reached as quickly as a xenon tube. The IA2521 incorporates
spread-spectrum switching to minimize EMI, is self-protected
against open-string conditions and thermal overloads, and is
available in an MSOP-8 and QFN16 3x3 packages.
Startup
The IA2521 device does not require a soft-start. It has a current
limit that is designed to avoid damage to the IC even by a short
circuit. At startup, then, it simply runs at maximum current until
the output capacitor is charged to the voltage necessary to get
the current set for the LED, at which time it enters normal
operation.
In normal operation, it is anticipated that the IA2521 will be
started up in torch mode.
Normal Operation
In normal operation, the IA2521 device either boosts or bucks
the input voltage to another DC voltage, whichever is necessary
to obtain the set LED current. The current is regulated by
measuring internally the output current, and regulating the DC
output voltage to be such that the current is as set.
Output current is set by the combination of the two resistors
attached to the two ISET pins. The ITORCH pin must always
have a resistor to ground. The IFLASH pin may be open, or have
a resistor to ground; it may be attached directly to a logic level
control.
When the IFLASH pin is open, the output current of the IA2521
is:
When the IFLASH pin has a resistor to ground, the output
current of the IA2521 is:
I
=
=
⎛
⎜
⎝
125
125
mA
mA
×
×
RTORCH
RTORCH
280
280
K
K
Ω
Ω
⎞
⎟
⎠
+
⎛
⎜
⎝
500
mA
×
RFLASH
70
K
Ω
⎞
⎟
⎠
resistor will be nominally at 140KΩ.
Flash-Mode Operation
To operate the IA2521 as a camera flash driver, recommended
operation is to first enable the IC, with the IFLASH resistor
open. The IA2521 will come up and regulate the LED current at
the torch-mode setting in approximately 300µsec. After that,
the IFLASH resistor may be pulled to ground. The output
current to the LED will step from its torch-mode setting to its
flash-mode setting in approximately 100µsec, the same rise
time as seen in typical xenon-flash tubes.
Input Capacitor
It may be desirable to include an input capacitor to this circuit.
Even when the input to the converter is a battery, batteries
have limited ability to source high-frequency currents. Thus,
there may be significant voltage drops at the input unless an
input capacitor is used.
NOTE: The input capacitor must be rated to take the AC ripple
current.
Output Capacitor
Typical usage will require a ceramic capacitor at the output of
the converter. The output capacitor of a boost converter sees
high ripple current. The capacitor must be rated to take this
current.
Enable
The IA2521 device can be turned off by pulling the ENABLE pin
low. In this condition, there is extremely low leakage current
into the IC, and no current into the LED.
Open LED
If the output of the IA2521 device is open, as might happen if
the LED fails open, the output voltage of the IA2521 will go up
to approximately 6V. The IC will not be damaged by this
condition.
Thermal Shutdown
If the IA2521 device die becomes excessively hot, the IC will
shut itself down. It will then resume normal operation after
cooling down sufficiently.
Since the torch mode is nominally at 250mA, the torch mode
IA2521
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