POWER LP3359-MSF High performance, current source for parallel white-led driver Datasheet

LP3359
High performance, Current Source
For Parallel White-LED Driver
General Description
Features
The LP3359 is a parallel white-LED driver with four
matched current outputs. It can supply a total output
current of 100mA over an input voltage range of 3.0V to
5.5V. The amount of constant current sourced to the
outputs is user selectable using one external sense
resistor. LP3359 typically draws 0.01µA when placed in
shutdown, and 180µA when operating in the no-load
condition. If any of the outputs are not used, leave the
pin(s) unconnected.
Brightness can be controlled by PWM techniques or by
adding a DC voltage. A PWM signal can be applied to
the EN/PWM pin to vary the perceived brightness of the
LED.
The LP3359 uses an active-high enable level. The
LP3359 is available in DFN-8 and TSSOP-8 package.
Ordering Information
LP3359 - □ □
Regulated IOUT With ± 0.3% Matching Between
Constant Current Outputs
Drives One, Two, Three or Four White LED’s with
No Ballast Resistors
3.0V to 5.5V Input Voltage
Up to 100mA Output Current
Active-High Enable
Very Small Solution Size
Very Low Shutdown Current (0.01µA typical)
Available in DFN-8 ,TSSOP-8 Package
RoHS Compliant and 100% Lead(Pb)-Free
Applications
Cellular and Smart mobile phone
PDA/DSC
LCD Display
Typical Application Circuit
□
LP3359
F: PB-Free
Package
MS: MSOP-8
QV: DFN-8
Pin Configurations
LP3359-datasheet
Ver.1.1
Nov.-2005
1 -1
LP3359
Functional Pin Description
Pin Number
Pin Name
Pin Function
1
Vin
Input Voltage
2
GND
3
EN/PWM
4
Iset
5-8
LEDx
Power Ground.
Active-High Enable Input – There is no internal pull-down resistor.
Current Set Input-The resistor value tied between this pin and ground sets the
output current.
Current Source Outputs 1- 4 - Connect directly to LED’s
Function Block Diagram
Fig1.
LP3359 Block Diagram
Absolute Maximum Ratings
VIN ------------------------------------------------------------------------------------------------------------------0.3V to 6V max
EN/PWM-----------------------------------------------------------------------------------------0.3V to (VIN+0.3V) w/ 6 max
Continuous Power Dissipation ---------------------------------------------------------------------- Internally Limited
DFN-8L , 3 ×3,θJA -------------------------------------------------------------------------------------------------------- 50°C/W
TSSOP-8L , θJA ----------------------------------------------------------------------------------------------------------- 70°C/W
Junction Temperature (TJ ) ---------------------------------------------------------------------------------------------150°C
Storage Temperature Range ------------------------------------------------------------------------------ -65°C to 150°C
Lead Temp (Soldering, 5sec) ------------------------------------------------------------------------------------------ 260°C
ESD Rating Human Body Model -----------------------------------------------------------------------------------------2kV
Operating Conditions
Input Voltage (VIN) -------------------------------------------------------------------------------------------------- 3V to 5.5V
Ambient Temperature (TA) ---------------------------------------------------------------------------------- -40°C to 85°C
LP3359-datasheet
Ver.1.1
Nov.-2005
2 -2
LP3359
Electrical Characteristics
(Limits in standard typeface and typical values apply for TA=25°C. Limits in boldface type apply over the operating junction temperature
range (-40°C~+85°C). Unless otherwise specified: VIN=5V, VLEDX=3.6V, RSET=7.5k, V(EN/PWM)=VIN.)
Symbol
ILEDx
ILEDX-MATCH
Description
Conditions
Min
3.0V ≤ VIN ≤ 5.5V 2.0V ≤ VLEDX ≤
LED Current
(VIN-0.4V) RSET=7.5k
14.3
Current Matching Between
Typ
Max
15.8
17.3
±0.3
±1
Units
mA
%
Any Two Outputs
VSET
1.06
ISET Pin Voltage
(-8%)
Output Current to Current
ILEDX/ISET
VHR
1.3
1.18
(+8%)
V
100
Set Ratio
Current Source Headroom
ILED=95% × ILED(nom), RSET= 4.7K
Voltage
(ILED(nom) approx. 25mA)
ILED=95% × ILED(nom), RSET= 12K
320
440
mV
130
220
175
285
uA
1
V
(ILED(nom) approx. 10mA)
ILED=0mA, RSET=Open
IQ
Quiescent Supply Current
325
ILED=0mA, RSET=7.5k
ISHUT-DOWN
Shutdown Supply Current
LP3359-datasheet
Ver.1.1
0.01
EN/PWM=0
Nov.-2005
3 -3
LP3359
Typical Operating Characteristics
LP3359-datasheet
Ver.1.1
Nov.-2005
4 -4
LP3359
Applications Information
should be avoided.
Enable/Shutdown
When the voltage on the active-high-logic enable pin is
low, the LP3359 will be in shutdown. While disabled, the
LP3359 typically draws 0.01µA. There is no internal
pull-up or pull-down on the PWM pin of the LP3359, Do
not let PWM pin floating.
Output Current Capability
The LP3359 is capable of providing up to 25mA of
current to each of the four outputs given an input voltage
of 3.0V to 5.5V. The outputs have a typical current
matching of ± 0.3% between adjacent sources. An
external resistor can be used to set the output current, as
approximated with the following the equation:
In order for the output currents to be regulated properly,
sufficient headroom voltage (VHR) must be present. The
headroom voltage refers to the minimum amount of
voltage that must be present across the current source in
order to ensure the desired current is realizable. To
ensure the desired current is obtained, apply the
following equations to find the minimum input voltage
required:
VLEDX is the diode forward voltage, and VHR is
defined by the following equation:
ILEDX is the desired diode current, and kHR, typically
15mV/mA in the LP3359, is a proportionality constant
that represents the ON-resistance of the internal current
mirror transistors. For worst-case design calculations,
using a kHR of 20mV/mA is recommended. (Worst-case
recommendation accounts for parameter shifts from
part-to-part variation and applies over the full operating
temperature range). Changes in headroom voltage from
one output to the next, possible with LED forward voltage
mismatch, will result in different output currents and LED
brightness mismatch. Thus, operating the LP3359 with
insufficient headroom voltage across all current sources
LP3359-datasheet
Ver.1.1
Nov.-2005
Brightness Control
(1)Using a PWM Signal to EN/PWM Pin
Brightness control can be implemented by pulsing a
signal at the PWM pin. The RSET value should be
selected using the RSET equation. LED brightness is
proportional to the duty cycle (D) of the PWM signal.
For linear brightness control over the full duty cycle
adjustment range, the PWM frequency (f) should be
limited to accommodate the turn-on time (TON = 20µs)
of the de- vice.
If the PWM frequency is much less than 100Hz, flicker
may be seen in the LEDs. For the LP3359, zero duty
cycle will turn off the LEDs and a 50% duty cycle will
result in an average ILED being half of the
programmed LED current. For example, if RSET is set
to program 15mA, a 50% duty cycle will result in an
average ILED of 7.5mA, LED being half the
programmed LED current. RSET should be chosen not
to exceed the maximum current delivery capability of
the device.
(2)Using a DC Voltage Added to RSET
Using an analog input voltage VADJ via a resister
RADJ connects to the RSET pin can also be used to
achieve setting LED current. Figure 3 shows this
application circuit. For this application the LED's
current can be derived from the following Equation.
Figure 4 and table 2 shows the relation between VADJ
and ILED of a typical application example, where the
VADJ from 0 to 2.5V, RSET equals 11.5kΩ and RADJ
5 -5
LP3359
equals 12.5kΩ.
the LED process variations due to the constant current outputs
of the LP3359.
Parallel LEDx Outputs for Increased Current Driver
Outputs LED1 through LED4 may be connected together in
any combination to drive higher currents through fewer
LEDs. For example in Figure 5, outputs LED1 and LED2 are
connected together to drive one LED while LED3 and LED4
are connected together to drive a second LED.
Figure 5. Two Parallel Connected LEDs
With this configuration, two parallel current sources of equal
value provide current to each LED. RSET should therefore be
chosen so that the current through each output is programmed
to 50% of the desired current through the parallel connected
LEDs. For example, if 30mA is the desired drive current for 2
parallel connected LEDs, RSET should be selected so that the
current through each of the outputs is 15mA. Other
combinations of parallel outputs may be implemented in
similar fashions, such as in Figure 6.
Figure4. LED current setting example
which using a DC voltage to Rset
VADJ(V)
0
0.2
0.4
0.6
0.8
1
1.2
ILED(mA)
19.7
18.1
16.5
14.9
13.3
11.7
10.1
VADJ(V)
1.4
1.6
1.8
2
2.2
2.4
2.5
ILED(mA)
8.5
6.9
5.3
3.7
2.1
0.5
0
LED Selection
The LP3359 is designed to drive white-LEDs with a typical
forward voltage of 3.0V to 4.0V. The maximum LED forward
voltage that the LP3359 can accommo -date is highly
dependant upon VIN and ILEDX (See the section on Output
Current Capability for more information on finding maximum
VLEDX.) For applications that demand color and brightness
matching, care must be taken to select LEDs from the same
chromaticity group. Forward current matching is assured over
LP3359-datasheet
Ver.1.1
Nov.-2005
Figure 6. One Parallel Connected LED
6 -6
LP3359
Connecting outputs in parallel does not affect internal
operation of the LP3359 and has no impact on the Electrical
Characteristics and limits previously presented. The available
diode output current, maximum diode voltage, and all other
specifications provided in the Electrical Characteristics table
apply to parallel output configurations, just as they do to the
standard 4-LED application circuit.
Where T is the maximum junction temperature, T is the
ambient temperature, and θ JA is the junction -to-ambient
thermal resistance of the specified package. The LP3359 come
in the DFN-8 package that has a junction-to-ambient thermal
resistance (θJA)equal to 50℃/W.This value of θJA is highly
dependant upon the layout of the PC board. The actual power
dissipated by the LP3359 follows the equation:
Power Consumption
It is recommended that power consumed by the circuit (VIN ×
IIN) be evaluated rather than power efficiency. Figure 7 shows
the power consumption of the LP3359 Typical Application
Circuit.
Where N equals the number of active outputs, VLEDX is the
LEDX LED forward voltage, and ILEDX is the current supplied
to the LEDX diode by the LP3359. Power dissipation must be
less than that allowed by the package. Please refer to the
Absolute Maximum Rating of the LP3359.
Input Capacitor Selection
The LP3359 is designed to run off of a fixed input voltage.
Depending on the stability and condition of this voltage rail, it
may be necessary to add a small input capacitor to help filter
out any noise that may be present on the line. In the event that
filtering is needed, surface mount multi-layer ceramic
capacitors are recommended. These capacitors are small and
inexpensive. A capacitance of 0.1µF is typically sufficient.
Figure 7. 4LEDs, LED VF=2.7V, ILED=15mA Power Dissipation
The maximum allowable power dissipation that this
package is capable of handling can be determined as
follows:
LP3359-datasheet
Ver.1.1
Nov.-2005
7 -7
LP3359
Applications Information
LP3359-datasheet
Ver.1.1
Nov.-2005
8 -8
LP3359
LP3359-datasheet
Ver.1.1
Nov.-2005
9 -9
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