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PDF EUP3618 Data sheet ( Hoja de datos )
| Número de pieza | EUP3618 | |
| Descripción | Charge Pump Flash LED Driver | |
| Fabricantes | Eutech | |
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Preliminary
EUP3618
Charge Pump Flash LED Driver
with Safety Timer
DESCRIPTION
The EUP3618 is a large-current charge pump designed
specifically for white LEDs used in camera flash
applications. Only one small bucket capacitor is
required to develop the output drive, providing a low
EMI solution compared with inductive boost
regulators.
The EUP3618 has two operation modes: Flash mode
and Movie mode. In Flash mode, the EUP3618 is
capable of delivering 500mA of regulated current for a
duration of 500ms or up to 700mA for a reduced
duration. A safety timer is also included to ensure the
LED can not be on indefinitely and overheat.
The EUP3618 is available in a 10-pin TDFN package.
FEATURES
Input Voltage Range — 2.7V to 5.5V
Flash and Movie — Two Selectable Modes
Up to 700mA Output Current — Flash Mode
Flash Mode Safety Timer Shut-Off
1X and 2X Automatic Mode for High
Efficiency
External Flash Control Pin for Synchronization
to a Camera Module or Graphics Controller
Short-Circuit, Over-Voltage, Over-Current and
Over-Temperature Protection
Soft-Start Functionality
3mm× 3mm TDFN-10 Package
RoHS Compliant and 100% Lead (Pb)-Free
Halogen-Free
APPLICATIONS
Mobile Camera Phones
Digital Cameras
PDAs with Built-In Cameras
Typical Application Circuit
DS3618 Ver0.1 Jul. 2012
Figure 1.
1
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1 page  
Preliminary
EUP3618
Applications Information
General Operation
The EUP3618 is a large-current charge pump
designed specifically for white LEDs used in camera
flash applications. 2.4MHZ fixed-frequency switching
allows for tiny extermal components and low output
ripple. The EUP3618 has two operation modes which
are pin selectable for either Flash or Movie mode.
Operation begins after the enbale pin CTRL receive a
logic high, the device goes through a soft-start mode
to reduce inrush current. The EUP3618 starts in the
1X mode, which acts like a linear regulator to control
the output current by sensing the feedback pin FB.
The load and supply conditions determine whether
the charge pump operates in 1X or 2X mode.
LED Current
The LED current is set by RFB and VFB,
ILED=VFB/RFB
(1)
When the time of the high held less than tHI(min.) or
the low held less than tLO(min.), this pulse is invalid.
Figure 3.
Over-Temperature Protection
The OTP circuit prevents the device from overheating
and experiencing a catastrophic failure. When the
junction temperature exceeds 150°C the device is
disable. It remains disabled until the junction
temperature drops below this threshold. Hysteresis is
included to prevent toggling between modes.
The feedback voltage VFB is difference between Flash
and Movie mode. When in Flash mode (FLASH is
high), the VFB is set by the resistor RSET connected
between the RSET pin and SGND. The voltage of FB
is
VFB=(1.2/RSET)*12.5KΩ
(2)
Where 1.2V is the internal bandgap reference voltage
and 12.5KΩ is an internal resistance used to scale the
RSET current. Typical values of RSET are 42KΩ to
170KΩ for a range of VFB=300mV to 75mV in Flash
mode.
In Movie mode (FLASH is low), the VFB is
programed by the pulse number of the CTRL input.
Table 1. Voltage of FB（RFB＝0.33Ω）
Pulse
VFB (typ)
ILED (typ)
1 50mV 151mA
2 60mV 182mA
3 70mV 212mA
4 85mV 256mA
5 100mV 303mA
6 120mV 364mA
7 140mV 424mA
≥8 170mV
515mA
Timing Control
The CTRL pin timing control required to meet as
shown in Figure 3. tHI and tLO is the duration of high
and low of input pulse signal. tLAT is the data latch
time, when CTRL has been held in the high state for
time greater than tLAT, the pulse signal is valid latched.
tOFF is the shutdown time, when CTRL has been held
in the low state for time greater than tOFF, the
EUP3618 enters into shutdown mode.
Over-Voltage Protection
Output OVP prevents the EUP3618 from generating
an output voltage that could damage other devices
connected to it such as load LEDs and bypass
capacitors. When the output voltage exceeds 5.8V, the
OVP circuit disables the charge pump until the
voltage decreases to a level within the acceptable
range. This circuit allows the device to drive LEDs
with high forward voltage at a reduced level without
exceding the output voltage limits specified for the
device.
Over-Current Protection
When the EUP3618 is in 2X mode, the input current
will be approximately double the required output.
When the steady-state load requires the maximum
current available in 2X mode, The OCP circuit
prevents the device from overheating from excessive
power dissipation. This feature protects the device
when in 1X mode.
Capacitor Selection
The EUP3618 charge pump circuit requires 3
capacitors：input，output and fly capacitors. A 1µF
capacitor is typically recommended. For the input
capacitor, a larger value of 2.2µF or 4.7µF will help
reduce input voltage ripple. All the capacitors should
be ceramic to obtain low ESR for high performance.
The input and output capacitors should be located as
close as possible to the VIN and VOUT pins to obtain
best bypassing, and the returns should be connected
directly to the PGND pin. And the fly capacitor will be
close to CP and CN pin.
DS3618 Ver0.1 Jul. 2012
5
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