AL8811

AL8811
Boost/Buck/Inverting DC-DC CONVERTER
Description
Pin Assignments
The AL8811 is a monolithic control circuit containing the primary
functions required for DC-to-DC converters. These devices consist of
an
internal
temperature
compensated
reference,
comparator,
controlled duty cycle oscillator with an active current limit circuit, driver
and high current output switch. This series is specifically designed for
incorporating in Boost, Buck and voltage-inverting applications with a
minimum number of external components.
Features

Operation from 3.0V to 20V Input

Low Standby Current

Current Limiting

Output Switch Current to 1.6A

Output Voltage Adjustable

Frequency Operation to 100 kHz

Precision 2% Reference
MSOP-8
Applications

Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)

Halogen and Antimony Free. “Green” Device (Note 3) Notes:

Low Voltage LED Lighting such as MR-16

General Purpose DC-DC Converter
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green"
and Lead-free.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
Typical Application Diagram
Electronic Transformer compatible MR16 lamp Simplified Schematic
AL8811
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AL8811
Pin Descriptions
Pin Name Pin Number
Current
Switch+
1
Current
Switch-
2
CT
GND
Feedback
VCC
Current
Sense
Current
Drive
3
4
5
6
7
8
Descriptions
Internal switch transistor collector:
Connect to Inductor for boost converter.
Connect to VCC for Buck or Inverting converter
Internal switch transistor emitter:
Connect to GND for boost converter
Connect to Inductor for buck or inverting converter
Timing Capacitor to control the switching frequency
Feedback pin for inverting input of internal comparator
Supply voltage pin
Peak Current Sense Input by monitoring the voltage drop across an external current sense
resistor to limit the peak current through the switch
Current drive collector:
Normally connected to VCC directly or via a resistor.
Functional Diagram
AL8811
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AL8811
Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
Symbol
Parameter
VCC
Power Supply Voltage
VIR
Comparator Input Voltage Range
Rating
20
Unit
V
-0.3 to +36
V
VC (SWITCH)
“Current Switch +” Collector Voltage
36
V
VE (SWITCH)
„Current Switch –„ Emitter Voltage (VPIN 1 = 36V)
36
V
VCE (SWITCH)
V
“Current Switch” Collector to Emitter Voltage
36
VC (DRIVER)
“Current Drive” Collector Voltage
36
V
IC (DRIVER)
“Current Drive” Collector Current
100
mA
“Current Switch” Current
1.6
A
PD
Power Dissipation (Note 4)
600
mW
JA
Thermal Resistance
130
C/W
+150
C
ISW
TMJ
Maximum Junction Temperature
TSTG
Storage Temperature Range
ESD HBM
ESD MM
Caution:
Human Body Model ESD Protection
Machine Model ESD Protection
-65 to +150
C
1
150
kV
V
Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only;
functional operation of the device at these or any other conditions exceeding those indicated in this specification is not implied. Device reliability may be
affected by exposure to absolute maximum rating conditions for extended periods of time.
Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling
and transporting these devices.
Recommended Operating Conditions
Parameter
Min
Max
Unit
Supply Voltage
Operating Junction Temperature Range
3
-40
20
+105
V
C
Symbol
VCC
TOP
Electrical Characteristics (@ VCC = 5V, TA = +25°C, unless otherwise specified.)
Symbol
OSCILLATOR
Parameter
Min
Typ
Max
Unit
kHz
fOSC
Frequency (VPIN 5 = 0V, CT = 1.0nF, TA = +25°C)
24
33
42
ICHG
Charge Current (VCC = 5.0V to 20V, TA = +25°C)
24
30
42
µA
Discharge Current (VCC = 5.0V to 20V, TA = +25°C)
140
200
260
µA
IDISCHG
IDISCHG/ ICHG
Discharge to Charge Current Ratio (Pin 7 to VCC, TA = +25°C)
5.2
6.5
7.5
—
VIPK (SENSE)
Current Limit Sense Voltage (ICHG = IDISCHG, TA = +25°C)
300
400
450
mV
—
1.0
1.3
V
Saturation Voltage, Darlington Connection
(ISW = 1.0A, ID = 50mA, Forced ß  20)
—
0.45
0.7
V
DC Current Gain (ISW = 1.0A, VCE = 5.0V, TA = +25°C)
50
75
—
—
Collector Off-State Current (VCE = 20V)
—
0.01
100
µA
1.225
1.25
1.275
V
Threshold Voltage Line Regulation (VCC = 3.0V to 20V)
—
1.4
6.0
mV
Supply Current (VCC = 5.0V to 20V, CT =1.0nF, Pin 7 = VCC,
VPIN 5 > Vth Pin 2 = Gnd, remaining pins open)
—
—
3.5
mA
OUTPUT SWITCH (Note 4)
Saturation Voltage, Darlington Connection
VCE(sat)
(ISW = 1.0A, Pins 1, 8 connected)
VCE(sat)
hFE
IC(off)
COMPARATOR
Vth
Reg(LINE)
Threshold Voltage TA = +25°C
TOTAL DEVICE
ICC
AL8811
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AL8811
Typical Performance Characteristics
Figure 1. Vce(sat) versus le
Figure 2. Reference Voltage versus Temp.
1.26
Reference Voltage (V)
Vce(sat), Saturation Voltage (V)
1.4
1.2
1
0.8
0.6
1.255
1.25
1.245
1.24
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0
10
20
30
Ie, Emitter Current (A)
Figure 3. Current Limit Sense Voltage
versus Temperature
Icc, Supply Current (mA)
Current Sense Voltage (mV)
400
380
360
340
20
30
40
50
60
70
80
90
100
3.0
2.5
2.0
1.5
1.0
100
0
5
10
15
20
25
30
35
40
Vcc, Supply Voltage (V)
Figure 6.Output Switch On-Off Time versus
Oscillator Timing Capacitor
1000
ton-off, Output Switch On-Off Time(us)
VCE ( sat), (V)
90
3.5
(oC)
1.8
Vcc=2~10V
Pin1,7,8=Vcc
Pin3,5=GND
TA=25oC
Pin2=5 10W
1.6
1.55
1.5
1.45
1.4
100
80
0.0
10
Figure 5. Emitter Follower Configuration
Output Saturation Voltage vs. Emitter Current
1.65
70
0.5
Temperature
1.7
60
4.0
420
1.75
50
Figure 4. Standby Supply Current
versus Supply Voltage
440
320
0
40
Temperature (oC)
300
500
AL8811
Document number: DS36090 Rev. 2 - 2
700
900
IE(mA)
1100
1300
1500
100
VCC = 5.0V
Pin 7 = VCC
Pin 5 = GND
TA = 25oC
ton
10
t off
1
0.1
0.01
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0.1
1
CT, Oscillator Timing Capacitor ( nF)
10
June 2013
© Diodes Incorporated
AL8811
Application Circuit
(1)
Boost Converter
Test
Conditions
Results
Line Regulation
VIN = 9V to 12V, IO = 200mA
20mV = ±0.035%
Load Regulation
VIN = 12V, IO = 50mA to 200mA
15mV = ±0.035%
Output Ripple
VIN = 12V, IO = 200mA
500mVPP
Efficiency
VIN = 12V, IO = 200mA
80%
AL8811
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AL8811
Application Circuit (cont.)
(2)
Electronic Transformer compatible triac dimmable MR16/GU5.3 lamp for 120Vac
Circuit Description
This design consists of three sections:
1) The input PFC circuit converts the 12VAC input voltage to a DC voltage around 30V (AL8811).
2) The output Buck LED Driver drives the three LEDs in series at a fixed current (AL8807A).
3) Finally, the phase-detect circuit generates a voltage proportional to the phase of the incoming AC voltage (when triac dimming is used).
PFC Circuit
The AL8811 Boost converter is a simple “Constant ON time controller”. By keeping the same ON time throughout the AC cycle, the circuit will
draw a current that will closely match the voltage and result in a constant input current. This eliminates the classic peak current problem with a
bridge rectifier and a large input filter capacitor.
The PFC circuit includes the input bridge rectifier, EMI filter (if needed) and the AL8811 Boost converter. The AC input voltage is rectified by the
bridge circuit and filtered by C1, R1, C4, and C5. This first filter removes the high frequency that is generated by the Electronic Transformer in the
range of 20-30 KHz. An additional diode rectifier circuit (D5, C2) is used to generate a voltage that is used to power the circuit that will turn on/off
the external MOSFET of the Boost converter. This circuit is very important as the gate drive of the MOSFET has to be greater than 3-4 volts
throughout the AC cycle. The external MOSFET is used to reduce the heat dissipation in the AL8811.
The AL8811 has a current limit resistor R3 which sets the maximum current allowed through the inductor L1. The output voltage is set by the
divider R6, R5 to an output of around 35 volts. The output voltage is filtered by the two capacitors C8 and C9. These two capacitors store energy
that will be used when the input voltage is low during the AC cycle.
AL8811
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AL8811
Application Circuit (cont.)
Buck LED Driver
The AL8807A is a step-down DC-DC converter designed to drive LEDs with a constant current. The current through the LED is controlled by R11.
In the present Evaluation board, the current is set to around 660mA based on a resistor value of 0.15Ω. The current is set using the “CTRL” input
pin which in this new version of the IC can vary from 0 to 2.5V, controlling the current from 0mA to the maximum current at 2.5V. This control input
pin is used to lower the LED current as the TRIAC dims the LED. In this way, the energy stored in the two output capacitors of the PFC circuit will
be able to provide current throughout the AC cycle.
TRIAC Phase Detection Circuit
The phase of the TRIAC is detected by using an additional rectifier circuit that generates a voltage in proportional to the phase of the TRIAC Driver.
This is done by rectifying the input AC voltage and averaging the energy using a resistor to charge a capacitor. Two additional resistors in series,
R12 and R8, slowly discharge this circuit so it will follow the input phase change. The two resistors, R12 and R8, are used to scale the voltage so
the range is from 0 to 2.6V to the Buck LED driver control pin.
A simple transistor emitter follower circuit is used to drive a 1KΩ resistor in the emitter circuit. This low resistance is needed to drive the input
control pin of the AL8807A LED driver because the pin outputs a small current of 50uA, which limits the lowest control voltage to around 50 mV.
Setting the LED output current (AL8807A):
The LED output current is set using resister R11 and the formula:
ILED = VTH / R11
where VTH is equal to 0.1V
For a current of 660mA, R11 is about 0.15Ω.
Setting the PFC Variables (AL8811)
The choice for the size of the boost converter inductor selected in this design is based on a compromise which it is able to support a peak current to
around 1.5A since the average input voltage will be around 12-14V.
The boost converter (AL8811) includes a current limit resistor R3 which will limit the current through the inductor and thus the power delivered to the
output load. The formula for the resistor is:
IPK(switch) = 0.33V / R3
For a current limit of 1A, R3 is 0.33Ω.
In this evaluation design, this value was selected based on having three LEDs in series drawing about 660mA. It was found that two 68µF
capacitors mounted in parallel would just fit into the cavity of the MR16 bulb. The important design goal is to have the PFC circuit, which is used to
always draw current from the Electronic Transformer.
AL8811
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AL8811
Application Circuit (cont.)
(3)
Buck Converter
Test
Line Regulation
VIN = 12V to 20V, IO = 500mA
Conditions
Results
20mV = ±0.2%
Load Regulation
VIN = 20V, IO = 50mA to 500mA
5mV = ±0.05%
Output Ripple
VIN = 20V, IO = 500mA
160mVPP
Efficiency
VIN = 20V, IO = 500mA
82%
1
8
Q2
Q1
Q S
R
7
2
I pk
CT
B240
Rsc
0.11
Osc
3
100uH
L
VCC
TC
470
pF
1.25V
Ref
Reg
1.0uH
100
+
Vin
20
+
Comp.
+
_
4
V out
6
470
uF
5
Vout
5.0V/500mA
R2
+
CO
36k
470uF
25k
R1
Optional Filter
AL8811
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AL8811
Application Circuit (cont.)
(4)
Voltage Inverting Converter
Test
Conditions
Results
Line Regulation
Vin = 4.5V to 6.0V, IO = 100mA
20mV = ±0.08%
Load Regulation
Vin = 5.0V, IO = 20mA to 100mA
30mV = ±0.12%
Output Ripple
Vin = 5.0V, IO = 100mA
500mVPP
Efficiency
Vin = 5.0V, IO = 100mA
60%
AL8811
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AL8811
Ordering Information
Part Number
Package Code
Packaging
AL8811M8-13
M8
MSOP-8
Quantity
NA
Tube
Part Number Suffix
NA
13” Tape and Reel
Quantity
Part Number Suffix
2500/Tape & Reel
-13
Marking Information
(1)
MSOP-8
( Top View )
8
7
6
Logo
5
YWX
AL8811
Part Number
2
1
3
Internal Code
Y : Year : 0~9
W : Week : A~Z : 1~26 week;
a~z : 27~52 week; z represents
52 and 53 week
4
Package Outline Dimensions (All dimensions in mm.)
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.
D
4x
10
°
0.25
E Gauge Plane
x
Seating Plane
a
y
4x10°
L
Detail C
1
b
E3
A3
A2
A
e
A1
AL8811
Document number: DS36090 Rev. 2 - 2
E1
c
See Detail C
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MSOP-8
Dim Min Max Typ
A
1.10
A1 0.05 0.15 0.10
A2 0.75 0.95 0.86
A3 0.29 0.49 0.39
b 0.22 0.38 0.30
c 0.08 0.23 0.15
D 2.90 3.10 3.00
E 4.70 5.10 4.90
E1 2.90 3.10 3.00
E3 2.85 3.05 2.95
e
0.65
L 0.40 0.80 0.60
a
0°
8°
4°
x
0.750
y
0.750
All Dimensions in mm
June 2013
© Diodes Incorporated
AL8811
Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.
X
C
Y
Dimensions Value (in mm)
C
0.650
X
0.450
Y
1.350
Y1
5.300
Y1
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AL8811
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