YB1315 Datasheet, PDF (8/10 Pages) YOBON TECHNOLOGIES,INC. – High Efficiency Charge Pump White LED Driver

Preliminary YB1315
High Efficiency Charge Pump White LED Driver
greater than the current through that of
R_SET.
The white LED can be estimated by
following equation:
I _LED
=
250
×
⎛
⎜
⎝
V_ISET
R_SET
⎞
⎟
⎠
To set the LED current, the device uses a
R_SET resistor connected the pin I_SET to
ground to generate a reference current
V_ISET/R_SET , where V_ISET is the voltage from
I_SET pin to ground.
This reference current is amplified by K
(250 typical) to generate the LED current.
Following table shows the relation between
R_SET and LED current.
Rset (KΩ) 6 7.5 10 15 150
Iled (mA) 25 20 15 10 1
Thermal Protection
The regulator has thermal shutdown
circuitry that protects it from damage
caused by high temperature conditions.
The thermal protection circuitry shut down
the device when the junction temperature
reached approximately 160℃, allowing the
device to cool. When the junction
temperature cools to approximately 140℃,
the device is automatically re-enabled.
Continuously running the regulator into
thermal shutdown can degrade reliability.
Under-voltage Lockout
The under-voltage lockout circuit shuts
down the device when the voltage at V_IN
drops below a typical threshold of 2.2V.
This prevents damage to the devices.
Power Efficiency
The battery current and efficiency of the
YB1315 are mostly dependent on the
charge pump mode of operation. To get the
best performance from the YB1315 it is
better to use LEDs with consistently lower
V_F voltage.
Lower V_F will keep the charge pump in 1x
mode longer and will uses less battery
current, extending the run time of the
battery. The power conversion efficiency of
the YB1315 can be calculated by adding
up the products of each LED current and
voltage and dividing it by the product of the
input voltage and current. With a fully
charged battery where the input voltage is
typically above the LED forward voltage,
the charge pump operates in the 1x mode
and efficiency is high. As the battery
discharges, there is a point where the
current sources no longer have enough
voltage overhead to maintain a constant
current regulation. At that point, the charge
pump switches into the 1.5x mode. The
conversion efficiency is lowest at the
crossover. When in 1x mode the voltage
conversion efficiency is defined as output
power divided by input power:
η = ^POUT = ^{VOUT × IOUT} ×100%
P_IN
V_IN × I _IN
I _IN = I_OUT + I_Q
η = ^POUT = ^{VOUT × IOUT} ×100%
P_IN V_IN × (I_OUT + I_Q )
When in 1.5x mode the voltage conversion
efficiency is as output power divided by
input power:
YB1315 Rev.0.1
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