ACE ACE70320AN+

 Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Description
The ACE703 is a PFM step-up DC-DC converter specifically designed to drive white LEDs with a
constant current. It can deliver stable constant output current from 0mA to 500mA by adjusting the
external resistor.
The ACE703 can drive one or more LEDs in parallel connection, also it can drive two in series, several
in parallel connection from one or two battery cells. With overvoltage limit protection circuit interiorly, the
chip and the external circuits will be safe even if the load is not connected. The device also can deliver
steady constant output voltage from 2.5V to 6.0V by adjusting the external resistor.
The ACE703 integrates stable reference circuits and it uses trimming technology in the process, so it can
afford high precision and low temperature-drift coefficient output current or output voltage.
The ACE703 devices are available in SOT-89-5 package.
Features
•
•
•
•
•
•
Low start-up voltage (when the output current is 1mA)--------------------------0.8V
The converter can output constant voltage from 2.5V to 6.0V or it can output constant current from
0 to 500mA by adjusting the external resistor.
Output current accuracy -----------±10%
Low temperature-drift coefficient of the output current------------------±100ppm/℃
Only four external components are necessary: an inductor, a Schottky diode, an output filter capacitor
and a resistor.
High conversion efficiency (When Vin=2.5V, for 1W LED)----------80%
Application
•
•
•
Power source for white LED
Supply constant current
Power source for a single or dual-cell battery-powered equipments
Absolute Maximum Ratings
Parameter
Symbol
Max
Unit
Input supply voltage
LX pin voltage
-0.3~10
V
-0.3 ~ Vout+0.3 V
CE pin voltage
IFB pin voltage
Lx pin output current
-0.3 ~ Vout+0.3 V
-0.3 ~ Vout+0.3 V
1.5
A
Power Dissipation [email protected]=25 OC
SOT-89-5
0.5
Junction temperature
Storage temperature
Operating free-air temperature
150
- 40 to 125
-20 ~ 85
W
O
C
C
O
C
O
VER 1.2
1 Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Packaging Type
SOT-89-5
5
1
4
2
3
Pin SOT-89-5
Function
IFB
1
Current feedback pin
VOUT
2
Output pin, power supply for internal circuits
CE
3
Chip enable pin (active high)
LX
4
Switching pin (Nch open drain)
GND
5
Ground pin
Ordering information
Selection Guide
ACE703 XX
XX +
H
Halogen - free
Pb - free
AN : SOT-89-5
Feedback Voltage
10…100mV / 20…200mV / 25…250 mV /
30…300 mV / 35…350 mV / 40…400 mV
VER 1.2
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Block Diagram
ACE703
Recommended Work Conditions
Item
Min Nom Max Unit
Input Voltage Range
0.8
Vout
V
Inductor
10
22
100 μH
Input capacitor
0
≧22
μF
Output capacitor
47
100 220
μF
Compensation capacitor
10
22
47
μF
Operating junction temperature -20
85
℃
*Suggestion: Tantalum capacitor is recommended to reduce the ripple of the output voltage
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Electrical Characteristics
(Vin=2.5V, VCE=Vout=3.3V,R=33Ω,TA=25°C, unless otherwise noted.)
Symbol
Item
Test conditions
VIFB
Feedback voltage
Iout=100mA
Vstart
Start-up voltage
Vhold
Hold-on voltage
IDD2*5
Quiescent current drawn from
power source
Inoload*6
Current with no load
ILX
ILXleak
LX switching current
LX leakage current
Ileak
Fosc
Maxdty
η
VCEH
VCEL
IOM
Stand-by current
Oscillator frequency
Oscillator duty cycle
Efficiency
CE “H” threshold voltage
CE “L” threshold voltage
Maximum output current
Iout=1mA,
Vin:0→2V
Iout=1mA,
Vin:2→0V
LX hung in air, VCE=VIFB=
Vout=3.3V, Vin=2.5V
OUT pin and IFB pin without any
load, VIFB=0
Vlx=0.4V,VIFB=0
Vout=Vlx=VIFB=6V,
Reference data
Min Typ. Max
80 100 120
180 200 220
230 250 270
280 300 320
330 350 370
380 400 420
0.8
0.6
0.7
0.6
V
20
30
uA
100
150
uA
1
mA
uA
0.5
uA
400
80
kHZ
%
%
V
V
mA
<
0.1
300
70
mV
V
700
Vout=3.3V, VCE=0, LX、IFB hung in
air
VIFB=0,
On(Vlx “L”)side
Iout=300mA
VCE:0→2V
VCE:2→0V
VIFB=0,Vout≡3.3V
0.9
Unit
350
75
80
0.9
0.3
500
0.6
Note:
1.Diode:schottky type, such as:1N5817,1N5819,1N5822
2.Inductor:22uH(R<0.5Ω)
3.Capacitor:100uF (Tantalum type)
4.Compensation capacitor:22uF (Tantalum type)
5.IDD2
is quiescent current drawn from power source, It is the minimum current of the chip without any dynamic current
6.Ino load is the current with no load in constant current application, it’s also the current consumed by the converter itself, including
the chip and external circuits, when Vin=2.5V,Vout=VOM
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Typical Application
(1) Constant output current application
Vin
D 1N5819
L
White LED
27uH
LX
OUT
ACE703
Power
Iout
Cin
47uF
CE
C1
22uF Tan
GND IFB
Cout
100uF Tan
Rc
(A) Drive only one white LED
ACE703
(B) Drive two white-LED in series and several in parallel connection
(2) Constant output voltage application
ACE703
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Detailed description
The ACE703 series are boost structure, voltage-type pulse-frequency modulation (PFM) step-up DC-DC
converter. It can deliver constant current or constant voltage. In constant current application, only five
external components are necessary to supply output current from 0 to 500mA:an inductor, an output filter
capacitor, a shottky diode, a compensation capacitor and a resistor which adjusts the output current. In
constant voltage application, to deliver adjustable and low noise output voltage from 2.5V to 6.0V, only six
external components are necessary as well: an inductor, a output filter capacitor, a shottky diode, a
compensation capacitor and two resistors for output voltage detect. The ACE703 device consists of
resistors for output voltage detection and trimming, a start-up voltage circuit, an oscillator, a reference
circuit, a PFM control circuit, a switch protection circuit, a voltage limit protection circuit and a driver
transistor.
● How to determine Rc in constant current application condition
We define output current is IOUT ,then Rc can be determined by Rc=VIFB/IOUT
For example, if we need Iout=100mA,and we choose the chip of VIFB=200mV,thus
Rc=200mV/100mA=2Ω
● How to determine R1,R2 in constant voltage application
We define output voltage is Vout, then R1/R2=VOUT/VIFB-1,R2 is in the range of 1KΩ~100KΩ.If we
need Vout =3.3V,and we choose the ACE703 of VIFB=400mV and select R2=4KΩ,thus R1=29KΩ.
In constant voltage application, we suggest using the high VIFB type ACE703,because there is voltage
ripple in existence on feedback voltage. When VIFB is high, the infection of the ripple is less than that of
low VIFB type, so the output is more stable.
The PFM control circuit is the core of the ACE703 IC. This block controls power switch on/off duty cycle
to stabilize output voltage by calculating results of other blocks which sense input voltage, output voltage,
output current and load conditions. In PFM modulation system, the frequency and pulse width is fixed.
The duty cycle is adjusted by skipping pulses, so that switch on-time is changed based on the conditions
such as input voltage, output current and load. The oscillate block inside ACE703 provides fixed
frequency and pulse width wave.
High-gain differential error amplifier guarantees stable output voltage at difference input voltage and load.
In order to reduce ripple and noise, the error amplifier is designed with high bandwidth.
Though at very low load condition, the quiescent current of chip do affect efficiency certainly. The four
main energy loss of Boost structure DC-DC converter in full load are the ESR of inductor, the voltage of
Schottky diode, on resistor of internal N-channel MOSFET and its driver. In order to improve the efficiency,
ACE703 integrates low on-resistor N-channel MOSFET and well designed driver circuits. The switch
energy loss is limited at very low level.
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Selection of the external components
Thus it can be seen, the inductor and shottky diode affect the conversion efficiency greatly. The inductor
and the capacitor also have great influence on the output voltage ripple of the converter. So it is
necessary to choose a suitable inductor, a capacitor and a right shottky diode, to obtain high efficiency,
low ripple and low noise.
Before discussion, we define: D≣VOUT-VIN/VOUT
(1) Inductor Selection
Above all, we should define the minimum value of the inductor that can ensure the boost DC-DC to
operate in the continuous current-mode condition.
L min ≥
D (1 − D ) 2 RL
2f
The above expression is got under conditions of continuous current mode, neglect Schottky diode’s
voltage, ESR of both inductor and capacitor. The actual value is greater that it. If inductor’s value is less
than Lmin,the efficiency of DC-DC converter will drop greatly, and the DC-DC circuit will not be stable.
Secondly, consider the ripple of the output voltage,
ΔI =
D • Vin
Lf
Im ax =
Vin
DVin
+
2
(1 − D ) RL
2 Lf
If inductor value is too small, the current ripple through it will be great. Then the current through diode
and power switch will be great. Because the power switch on chip is not ideal switch, the energy of switch
will improve. he efficiency will fall.
Thirdly, in general, smaller inductor values supply more output current while larger values start up with
lower input voltage and acquire high efficiency.
An inductor value of 3uH to 1mH works well in most applications. If DC-DC converter delivers large
output current (for example: output current is great than 50mA),large inductor value is recommended in
order to improve efficiency. If DC-DC must output very large current at low input supply voltage, small
inductor value is recommended.
The ESR of inductor will affect efficiency greatly. Suppose ESR value of inductor is Rl, Rload is load
resistor, then the energy can be calculated by following expression:
Δη ≈
rL
Rload (1 − D) 2
For example: input 1.5V,output is 3.0V,Rload=20Ω,rL=0.5Ω,The energy loss is 10%.
Consider all above, inductor value of 47uH.ESR<0.5Ω is recommended in most applications. Large
value is recommended in high efficiency applications and smaller value is recommended.
VER 1.2
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
(2) Capacitor Selection
Ignore ESR of capacitor, the ripple of output voltage is:
r=
ΔVout
D
=
Vout
Rload Cf
So large value capacitor is needed to reduce ripple. But too large capacitor value will slow down system
reaction and cost will improve. So 100uF capacitor is recommended. Larger capacitor value will be used
in large output current system. If output current is small (<10mA), small value is needed.
Consider ESR of capacitor, ripple will increase:
r' = r +
Im ax • RESR
Vout
When current is large, ripple caused by ESR will be main factor. It may be greater than 100mV.The ESR
will affects efficiency and increase energy loss. So low-ESR capacitor (for example: tantalum capacitor) is
recommend or connect two or more filter capacitors in parallel.
(3) Diode Selection
Rectifier diode will affects efficiency greatly,Though a common diode (such as 1N4148) will work well for
light load, it will reduce about 5%~10% efficiency for heavy load, For optimum performance, a Schottky
diode (such as 1N5817.1N5819.1N5822) is recommended.
(4) Input Capacitor
If supply voltage is stable, the DC-DC circuit can output low ripple, low noise and stable voltage without
input capacitor. If voltage source is far away from DC-DC circuit, input capacitor value greater than 10uF
is recommended.
(5) Resistor R1.R2 for output voltage detect
In constant current application,R1 and R2 can be selected by following expression:
Vout R1
=
+1
VIFB
R2
For example, when VIFB=400mV,Vout=3.3V.
If R2=4KΩ,then R1= Vout
=29KΩ;if R2=40KΩ,then R1=290 KΩ.
(
VIFB
− 1) × R 2
(6) Selection of L.C and compensation capacitor C1
When the load current is large(eg: Iout=100mA),the output voltage ripple will increase:
ΔVout ≈
L 2
I L + Vout 2 − Vout
C
As we can see, When output current is large, the maximum current of the inductor IL will increase, thus
the ripple of the output voltage will increase. To decrease the ripple, there are two ways:
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Firstly, select the appropriate value of L.C. It require the value of L*C be not too large, and the value of
L/C be small. For example, select L=22uH,C=100uF;or L=10uH,C=47uF;etc.
If select L/C>1(such as L=100uH,C=47uF),it is improper in large current(larger than 100mA)
application.
Secondly, add a compensation capacitor C1 to reduce the ripple. However, the value of the
compensation capacitor is different between constant current application and constant voltage mode.C1
and the resistor parallel connected with it will generate a pole, thus, it can compensate the syntonic
frequency made by L.C.
In constant voltage mode, if the resistor parallel connected with C1 is large,(eg: R1=290KΩ) then τ=R1‧
C1 is large, therefore, when C1≥0.1uF,the ripple can be decreased greatly.
But in constant current mode, the resistor parallel connected with C1 is just the equivalent resistor of the
white-LED, about 1Ω.Then,to maintain larger τ require larger compensation capacitor, normally between
10uF to 47uF.Many experiments have proved, when L=22uH,Cout=100uF,C1=22uF,the ripple of the
output voltage, the output current, and the feedback voltage is smallest, and the characteristic of the
constant current is excellent, even the efficiency is highest.
Test circuits
(1) Feedback voltage test circuit
ACE703
(2) Start-up voltage test circuit(Iload=1mA)
ACE703
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
(3) Hold-on voltage test circuit(Iload=1mA)
ACE703
(4) Quiescent current test circuit
ACE703
(5) Oscillator frequency and duty cycle test circuit
ACE703
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
(6) LX switching current test circuit
ACE703
(7) LX leakage current test circuit
ACE703
(8) CE“H"voltage test circuit
ACE703
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
(9) CE“L"voltage test circuit
ACE703
(10) Maximum output voltage (with no load) test circuit
ACE703
VER 1.2
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Typical Characteristic
(Recommended operating conditions: Cin=47uF, Cout=22uF, Cout=100uF,L=22uH Topt=25℃,unless otherwise
noted)
1. Output Voltage VS. Input Voltage
ACE70320AN+ Output Current VS. Input Voltage
Input Voltage (V)
3. Efficiency VS. Input Voltage
ACE70320AN+ Efficiency VS. Input Voltage (Iout=200mA)
Input Voltage (V)
5. Ripple Voltage VS. Input Voltage
ACE70320AN+ Ripple Voltage VS. input Voltage(Iout=100mA)
Input Voltage (V)
2. Efficiency VS. Input Voltage
ACE70320AN+ Efficiency VS. Input Voltage (Iout=100mA)
Input Voltage (V)
4. Efficiency VS. Input Voltage
ACE70320AN+ Efficiency VS. Input Voltage (Iout=300mA)
Input Voltage (V)
6. Ripple Voltage VS. Input Voltage
ACE70320AN+ Ripple Voltage VS. input Voltage(Iout=200mA)
Input Voltage (V)
VER 1.2
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
7. Ripple Voltage VS. Input Voltage
ACE70320AN+ Ripple Voltage VS. input Voltage(Iout=300mA)
Input Voltage (V)
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Packing Information
SOT-89-5
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Technology
ACE703
White LED PFM Step-Up DC-DC Converter
Notes
ACE does not assume any responsibility for use as critical components in life support devices or systems
without the express written approval of the president and general counsel of ACE Electronics Co., LTD.
As sued herein:
1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and shoes failure to perform when properly used in
accordance with instructions for use provided in the labeling, can be reasonably expected to result in
a significant injury to the user.
2. A critical component is any component of a life support device or system whose failure to perform can
be reasonably expected to cause the failure of the life support device or system, or to affect its safety
or effectiveness.
ACE Technology Co., LTD.
http://www.ace-ele.com/
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