NOT RECOMMENDED FOR NEW DESIGN
USE
AL8860
and
AL8861
AP8800
350mA LED STEP-DOWN CONVERTER
Description
The AP8800 is a step-down DC/DC converter designed to drive LEDs
with a constant current. The device can drive up to seven LEDs,
depending on the forward voltage of the LEDs, in series from a
voltage source of 8V to 28V. Series connection of the LEDs provides
identical LED currents resulting in uniform brightness and eliminates
the need for ballast resistors. The AP8800 switches at frequency up
to 0.6MHz. This allows the use of small size external components,
hence minimizing the PCB area needed.
Maximum output current of AP8800 is set via an external resistor
connected between the V
IN
and SET input pins. Dimming is achieved
by applying either a DC voltage or a PWM signal at the CTRL input
pin. An input voltage of 0.2V or lower at CTRL shuts down the output
at SW and puts the device into a low-current standby state.
Pin Assignments
SO-8
( Top View )
CTRL 1
RSVD
SW
2
3
AP8800
8
7
6
5
SET
NC
NC
V
IN
GND 4
MSOP-8
( Top View )
CTRL 1
RSVD
SW
2
3
AP8800
Features
LED Driving Current up to 350mA
Compatible with 12V & 24V Standard Systems
High Efficiency up to 92%
High Switching Frequency up to 0.6MHz
PWM/DC Input for Dimming Control
Built-in Soft-Start Function
Built-in Output Open-Circuit Protection
SO-8, MSOP-8 and U-DFN3030-10: Available in ―Green‖
Molding Compound (No Br, Sb) with lead Free Finish/ RoHS
Compliant
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
8
7
6
5
SET
NC
NC
V
IN
GND 4
U-DFN3030-10
( Top View )
CTRL
RSVD
NC
SW
1
2
3
4
5
10
9
SET
NC
NC
NC
V
IN
AP8800
8
7
6
Applications
Commercial & Industrial Lighting
Small LCD Panel Backlight
Architecture Detail Lighting
Appliances Interior Lighting
GND
Notes:
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS), 2011/65/EU (RoHS 2) & 2015/863/EU (RoHS 3) compliant.
2. See https://www.diodes.com/quality/lead-free/ 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 Applications Circuit
8V ~ 28V_DC
V
IN
CTRL
SET
R
SET
= 0.33Ω
D
1
AP8800
C
1
= 1
μ
F
GND
SW
L
1
= 100
μ
H
AP8800
Document number: DS31764 Rev. 8 - 3
1 of 13
www.diodes.com
1
April 2018
© Diodes Incorporated
NOT RECOMMENDED FOR NEW DESIGN
USE
AL8860
and
AL8861
AP8800
Pin Descriptions
Pin Name
SW
GND
SET
SO-8
3
4
8
Pin Number
MSOP-8 U-DFN3030-10
3
4
8
4
5
10
Function
Switch Pin. Connect inductor/freewheeling diode here. Minimize trace area at this pin to
reduce EMI.
GND Pin
Set Nominal Output Current Pin. To configure the output current of the device.
Dual function dimming control pin.
Input voltage of 0.2V or lower forces the device into low current standby mode and
shuts off the output.
A PWM signal (driven by an open-drain/collector source) allows the output current
to be adjusted over a wide range up to 100%.
CTRL
1
1
1
An analog voltage between 0.3V and 2.5V adjusts the output current between 25%
and 200% of the current set by 0.2V/R
S
.
The input impedance is about 200kΩ, and if the pin is left open V
CTRL
= V
REF
V
IN
RSVD
NC
5
2
6, 7
5
2
6, 7
6
2
2, 7, 8, 9
Input Supply Pin. Must be locally bypassed.
Reserved. Normally connected to Ground
No Connection.
Functional Block Diagram
Absolute Maximum Ratings
(@T
A
= +25° unless otherwise specified.)
C,
Symbol
V
IN
V
SET
VSW
V
CTRL
T
J
T
LEAD
T
ST
Caution:
Parameter
VIN Pin Voltage
Set Voltage Relative to V
IN
SW Voltage
CTRL Pin Input Voltage
Maximum Junction Temperature
Maximum Lead Temperature
Storage Temperature Range
Rating
-0.3 to +30
V
IN
-5 to V
IN
+0.3
-0.3 to +30
-0.3 to +5
+125
+300
-55 to +125
Unit
V
V
V
V
°
C
°
C
°
C
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.
AP8800
Document number: DS31764 Rev. 8 - 3
2 of 13
www.diodes.com
April 2018
© Diodes Incorporated
NOT RECOMMENDED FOR NEW DESIGN
USE
AL8860
and
AL8861
AP8800
Recommended Operating Conditions
(@T
A
= +25° unless otherwise specified.)
C,
Symbol
V
IN
V
CTRLDC
V
CTRLL
f
OSC
T
A
Duty Cycle
V
ENH
V
ENL
Notes:
4.
5.
Parameter
Operating Input Voltage relative to GND
Voltage Range for 24% to 200% DC Dimming Relative to GND (Note 4)
Voltage Low for PWM Dimming Relative to GND
Maximum Switching Frequency
Ambient Temperature Range
Using Inductor ≥ 100µH (Note 5)
CTRL Input Voltage to Attain 100% LED Current
CTRL Input Voltage Below Which Device Turns Off
Min
8.0
0.3
0
—
-40
0.1
1.25
—
Max
28
2.5
0.2
500
+85
0.95
—
0.2
Unit
V
V
V
kHz
°
C
—
V
For 100% brightness either leave floating or connect to 1.25V relative to GND.
For most applications the LED current will be within 8% over the duty cycle range specified. Duty cycle accuracy is also dependent on propagation
delay. Smaller size inductors can be used but LED current accuracy may be greater than 8% at extremes of duty cycle. This is most noticeable at low
duty cycles (less than 0.1) or when the input voltage is high and only one LED is being driven.
Electrical Characteristics
(@T
A
= +25° unless otherwise specified.)
C,
Symbol
I
OUT
I
Q
V
THD
V
REF
SET
R
DS(ON)
I
SW_Leakage
JA
Parameter
Continuous Switch Current
Quiescient Current
Internal Current Sense Threshold Voltage
Internal Reference Voltage
SET Pin Input Current
On-Resistance of Internal Switch
Switch Pin Leakage Current
Thermal Resistance Junction-to-Ambient
(Note 6)
—
V
IN
– V
SET
—
V
SET
= V
IN
-0.1
—
—
SO-8 (Note 7)
MSOP-8 (Note 7)
U-DFN3030-10 (Note 7)
SO-8 (Note 7)
JC
Notes:
Conditions
Min
—
—
92
—
—
—
—
—
—
—
—
—
—
Typ
—
20
100
1.25
1.3
1.7
—
92
120
46
60
98
32
Max
350
30
108
—
—
2.2
5
—
—
—
—
—
—
Unit
mA
μA
mV
V
μA
Ω
μA
C/W
C/W
C/W
C/W
C/W
C/W
Thermal Resistance Junction-to-Case
MSOP-8 (Note 7)
U-DFN3030-10 (Note 7)
6. Refer to figure 8 for the device derating curve.
7. Test condition for SO-8, MSOP-8 and U-DFN3030-10: Device mounted on FR-4 PCB, 2‖x 2‖, 2oz copper, minimum recommended pad layout on
top layer and thermal vias to bottom layer ground plane. For better thermal performance, larger copper pad for heat-sink is needed.
AP8800
Document number: DS31764 Rev. 8 - 3
3 of 13
www.diodes.com
April 2018
© Diodes Incorporated
NOT RECOMMENDED FOR NEW DESIGN
USE
AL8860
and
AL8861
AP8800
Application Information
AP8800 Operation
The AP8800 is a hysteretic LED current switching regulator sometimes known as an equal ripple switching regulator. In normal operation, when
voltage is applied at +V
IN
(See Figure 1), the AP8800 internal switch is turned on. Current starts to flow through sense resistor R
1
, inductor L1,
and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input voltage +V
IN
, and the inductor L1 (See Figure 2).
8V ~ 28V_DC
V
IN
CTRL
SET
R
SET
= 0.33Ω
D
1
AP8800
C
1
= 1
μ
F
GND
SW
L
1
= 100
μ
H
Figure 1 Typical Configuration
This rising current produces a voltage ramp across R
SET
. The internal circuit of the AP8800 senses the voltage across R
SET
and applies a
proportional voltage to the input of the internal comparator.
When this voltage reaches an internally set upper threshold, the internal switch is turned off. The inductor current continues to flow through R
SET
,
L1, the LEDs and the schottky diode D1, and back to the supply rail, but it decays, with the rate of decay determined by the forward voltage drop
of the LEDs and the schottky diode.
This decaying current produces a falling voltage at R
SET
, which is sensed by the AP8800. A voltage proportional to the sense voltage across
R
SET
is applied at the input of the internal comparator. When this voltage falls to the internally set lower threshold, the internal switch is turned on
again. This switch-on-and-off cycle continues to provide the average LED current set by the sense resistor R
SET,
with a switching current
determined by the input voltage and LED chain voltage.
In normal operation the off time is relatively constant (determined mainly by the LED chain voltage) with only the on-time varying as the input
voltage changes. At duty cycles up to around 80% the ramp of the LED/switch current is very linear; however, as the duty cycle approaches 95%
the LED current ramp starts to become more exponential. This has two effects:
1.
2.
The overall on time starts to increase lowering the overall switching frequency.
The average LED current starts to increase – which may impact accuracy.
AP8800
Document number: DS31764 Rev. 8 - 3
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1
Figure 2 Typical Switching Waveform
April 2018
© Diodes Incorporated
NOT RECOMMENDED FOR NEW DESIGN
USE
AL8860
and
AL8861
AP8800
Application Information
(Cont.)
Inductor Selection
A 100μH inductor is recommended for most AP8800 applications with input voltage at 24V.
Figure 3 displays the resulting switching frequency varying the main circuit parameters: Supply voltage, Inductor value and number of LEDs to be
driven.
Switching Frequency
700
600
500
Frequency [kHz]
400
68
300
100
200
100
470
0
0
50
100
150
200
250
300
350
400
450
500
Inductor Value [H]
150
220
470
220
47
150
12V - 1LED
24V - 3 LEDs
28V - 4LEDs
100
Figure 3 Switching Frequency vs. Supply Voltage, Inductor, and Number of LEDs
Capacitor Selection
The small size of ceramic capacitors makes them ideal for AP8800 applications. X5R and X7R types are recommended because they retain their
capacitance over wider voltage and temperature ranges than other types such as Z5U. A 1μF input capacitor is sufficient for most intended
applications of AP8800.
Diode Selection
Schottky diode, e.g. B140, with their low forward voltage drop and fast reverse recovery, is the ideal choice for AP8800 applications.
Miscellaneous
To ensure optimal performance, RSVD pin should be connected to the GND pin with the shortest trace length.
AP8800
Document number: DS31764 Rev. 8 - 3
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April 2018
© Diodes Incorporated
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