FAN5616 Datasheet, PDF (8/14 Pages) Fairchild Semiconductor – High-Efficiency, Constant-Current LED Driver with Adaptive Charge Pump

Block Diagram
1µF
V_IN
EN1
EN2
V_SET
Linear
Regulator
On Off and
LED Current
Control
Oscillator
Voltage
Selector
Drivers
VOUT
Pump
Power
Good
Ref1
Bandgap
Reference
Reference
Range Selection
Low Battery Ref.
Regulator
Ref3
5µF
Analog
Detector
Ref2
Mode Change
V_IN
Ref4 (BG)
GND
1µF
Figure 3. Block Diagram
Circuit Description
As shown in Figure 4, the FAN5616’s switch capacitor
DC/DC converter automatically configures its internal
switches to achieve high efficiency and to provide tightly-
regulated output currents for the LEDs. An analog detec-
tor determines which diode requires the highest voltage
in order to sustain the pre-set current levels, and adjusts
the pump regulator accordingly. Every diode has its own
linear current regulator. In addition, a voltage regulator
controls the output voltage when the battery voltage is
within a range where linear regulation can provide maxi-
mum possible efficiency. If the battery voltage is too low
to sustain the diode current in linear mode, a fractional
3:2 charge pump is enabled. When the battery voltage
drops and the mode is no longer sufficient to sustain
proper operation, the pump is automatically reconfigured
to operate in 2:1 mode. As the battery discharges and
the voltage decays, the FAN5616 switches between
modes to maintain a constant current through the LEDs
throughout the battery life. This transition has hysteresis
to prevent toggling.
The internal supply voltage of the device is automatically
selected from the V_IN or V_OUT pins, whichever has a
higher voltage.
The FAN5616 enters shutdown mode to reduce overall
current consumption when both DAC inputs (EN1 and
EN2) are low.
Short Circuit and Thermal Protection
In the event of an output voltage short circuit, the output
current will be limited to a typical value of 65mA.
In addition, when the die temperature exceeds 150°C, a
reset occurs and remains in effect until the die cools to
135°C. At which time the circuit will restart and resume
normal operation.
8
FAN5616 Rev. 1.0.0
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