Diodes AP6508 User Manual
F
FIC
C
Y
500kHz 21V 3A SYNCHRONOUS DC/DC BUCK CONVERTER
Description
The AP6508 is a 500kHz switching frequency internal
compensated synchronous DCDC buck converter. It has
integrated compensation, and low R
MOSFETs.
The AP6508 enables continues load current of up t o 3A with
efficiency as high as 93%.
The AP6508 features current mode control operation, which
enables fast transient response times and easy loop
stabilization.
The AP6508 has external programmable softstart and a
Power Good indicator enabling sequencing and ramp control.
The AP6508 simplifies board layout and reduces space
requirements with its high level of integration and minimal
need for external components, making it ideal for distributed
power architectures.
The AP6508 is available in a standard Green DFN4030-14
package with exposed PAD for improved thermal
NEW PRODUCT
performance and is RoHS compliant.
high and low side
DSON
Pin Assignments
1
IN
2
SW
3
SW
4
SW
5
SW
BST
7
EN
(Top View)
Exposed Pad
DFN4030-14
AP6508
14
AGND
13
GND
12
GND
11
VCC
10
SS
96
PG
8
FB
Features
• VIN 4.5V to 21V
• V
• 500kHz switching frequency
• Enable pin
• External Softstart
• Power Good
• Protection
adjustable to 0.8V
OUT
o OCP
Applications
• Gaming Consoles
• TV sets and Monitors
• Set Top Boxes
• Distributed power systems
• Home Audio
• Consumer electronics
o Thermal Shutdown
• Lead Free Finish/ RoHS Compliant (Note 1)
Note: 1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at
http://www.diodes.com/products/lead_free.html.
Typical Application Circuit
100
90
80
(%)
70
IEN
V = 12V
IN
V = 5V
OUT
L = 3.3µH
60
E
50
40
0
1
LOAD CURRENT (A)
Efficiency vs. Load Current
AP6508
Document number: DS33437 Rev. 5 - 2
2
3
Typical Application Circuit
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October 2011
© Diodes Incorporated
Pin Descriptions
Pin # Name Description
1 IN
2,3,4,5 SW Switch Output. Use wide PCB trace to make the connection.
6 BST
7 EN
8 FB
9 PG Power Good
10 SS External Softstart
11
NEW PRODUCT
12, 13 GND
14 AGND Analog Ground
Exposed PAD
Functional Block Diagram
V
CC
AP6508
500kHz 21V 3A SYNCHRONOUS DC/DC BUCK CONVERTER
Supply Voltage. The AP6508 operates from a 4.5V to 21V input rail. C1 is needed to
decouple the input rail. Use wide PCB trace to make the connection.
Bootstrap. A capacitor connected between SW and BS pins is required to form a floating
supply across the high-side switch driver.
EN=1 to enable the chip. For automatic start-up, connect EN pin to VIN by proper EN resistor
divider as Figure 1 shows.
Feedback. An external resistor divider from the output to GND, tapped to the FB pin, sets the
output voltage. To prevent current limit run away during a short circuit fault condition the
frequency fold-back comparator lowers the oscillator frequency when the FB voltage is below
500mV.
BIAS Supply. Decouple with 0.μ1F – 0.22μF cap. And the capacitance should be no mor e
than 0.22μF
System Ground. This pin is the reference ground for the regulated output voltage. For this
reason care must be taken in its PCB layout. Suggested to be connected to GND with copper
and vias.
No internal connection. It is recommended to connect exposed pad to GND plane for optimal
thermal performance
1
IN
VCC
PG
EN
SS
FB
11
9
7
10
8
VCC
REGULATOR
REFERENCE
AP6508
Document number: DS33437 Rev. 5 - 2
Power Good Comparator
OSCILLATOR
ERROR AMPLIFIER
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50pF
CURRENT
LIMIT
COMPARATOR
1pF
200k
+
EA
+
-
BOOST
REGULATOR
+
LOGIC
-
+
-
PWM
COMPARATOR
CURRENT SENSING
AMPLIFIER
-
+
14
AGND
HS
DRIVER
VCC
LS
DRIVER
-
+
BST
6
SW
2
3
4
5
GND
12
13
October 2011
© Diodes Incorporated
AP6508
Absolute Maximum Ratings (Note 2)
Symbol Parameter Rating Unit
VIN
VSW
VBS
VFB
VEN
V
COMP
TST
TJ
TL
ESD Susceptibility (Note 3)
HBM Human Body Model 3 kV
NEW PRODUCT
Thermal Resistance (Note 4)
MM Machine Model 300 V
Symbol Parameter Rating Unit
θ
JA
θ
JC
Recommended Operating Conditions (Note 5)
Symbol Parameter Min Max Unit
VIN
TA
Notes: 2. 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.
3. 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 device.
4. Test condition for SO-8EP: Device mounted on 2"*2" FR-4 substrate PC board, 2oz copper, with minimum recommended pad on top layer and
thermal vias to bottom layer ground plane.
5. The device function is not guaranteed outside of the recommended operating conditions.
AP6508
Document number: DS33437 Rev. 5 - 2
Supply Voltage
Switch Node Voltage -0.3 to 23 V
Bootstrap Voltage VSW + 6 V
Feedback Voltage –0.3V to +6 V
Enable/UVLO Voltage –0.3V to +6 V
Comp Voltage –0.3V to +6 V
Storage Temperature -65 to +150 °C
Junction Temperature +150 °C
Lead Temperature +260 °C
Junction to Ambient 52 °C/W
Junction to Case 11 °C/W
Supply Voltage
Operating Ambient Temperature Range
500kHz 21V 3A SYNCHRONOUS DC/DC BUCK CONVERTER
22
4.5
-40
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21 V
+85 °C
© Diodes Incorporated
V
October 2011
Electrical Characteristics (V
Symbol Parameter Test Conditions Min Typ. Max Unit
IIN
IIN
R
DS(ON)1
R
DS(ON)2
SW
LKG
I
Limit
FSW
FFB
D
MAX
VFB
IFB
V
NEW PRODUCT
EN_Rising
V
EN_HYS
IEN
EN
TD-Off
PG
Vth-Hi
PG
Vth-Lo
PGTD
VPG
I
PG_LEAK
ISS
INUV
INUV
HYS
VCC VCC Regulator
TSD
Note: 6. Guaranteed by design
Shutdown Supply Current
Supply Current (Quiescent)
High-Side Switch On-Resistance
(Note 6) 120 mΩ
Low-Side Switch On-Resistance
(Note 6) 20 mΩ
Switch Leakage Current
Current Limit 5.8 A
Oscillator Frequency
Fold-back Frequency
Maximum Duty Cycle
Feedback Voltage
Feedback Current
EN Rising Threshold 1.1 1.3 1.5 V
EN Threshold Hysteresis 0.4 V
EN Input Current
EN Turn Off Delay
(Note 6) 5
Power Good Rising Threshold 0.9
Power Good Falling Threshold 0.7
Power Good Delay 20
Power Good Sink Current Capability 0.4
Power Good Leakage Current 50
Soft-Start Current 10.5
V
Vth
Under Voltage Threshold Rising
IN
V
Under Voltage Threshold
IN
Hysteresis
V
Load Regulation
CC
Thermal Shutdown 140 °C
AP6508
500kHz 21V 3A SYNCHRONOUS DC/DC BUCK CONVERTER
= 12V, TA = +25°C, unless otherwise noted)
IN
VEN = 0V
VEN = 2.0V, VFB = 1.0V
V
= 0V, VSW = 0V
EN
V
= 0.75V
FB
V
= 300mV
FB
VFB = 700mV
TA = -40°C to +85°C
V
= 800mV
FB
= 2V
V
EN
VEN = 0V
4.0 4.2 4.4
200 mV
5 V
Icc=5mA 5 %
0 µA
1.2 mA
0 10 µA
350 500 650 kHz
0.3
fSW
80 85 %
791 807 823 mV
10 50 nA
2
0
μA
μs
VFB
VFB
μs
V
nA
μA
V
AP6508
Document number: DS33437 Rev. 5 - 2
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October 2011
© Diodes Incorporated
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Typical Performance Characteristics
1.3
1.25
1.2
1.15
1.1
1.05
QUIESCENT SUPPLY CURRENT (mA)
NEW PRODUCT
1
5.05
5.045
0
5
Quiescent Supply Current vs. Input Voltage
10 15 20 25
INPUT VOLTAGE
AP6508
500kHz 21V 3A SYNCHRONOUS DC/DC BUCK CONVERTER
20
18
16
ENT (µA)
14
12
10
8
6
WN SUPPL
4
2
SHUTD
0
0 5 10 15 25
Shutdown Supply Current vs. Input Voltage
INPUT VOLTAGE ( V)
7
6.8
6.6
20
V = 12V
IN
V = 1.2V
OUT
6.4
1.208
1.206
(V)
1.204
G
1.202
VOL
1.198
O
1.196
1.194
1.192
(A)
6.2
LI
5.8
5.6
5.4
5.2
1.21
1.2
6
5
-10-20 0 2010 30 5040 60 8070 90
-40
TEMPERATURE (°C)
Current Li m it vs. Temperature
V = 12V
IN
V = 5V
IN
11.500.5 2.532
OUTPUT CURRENT (A)
Load Regulation vs. Output Current
October 2011
© Diodes Incorporated
5.04
5.035
CC
V (V)
5.03
5.025
5.02
0 5 10 15 20 25
1.225
1.2245
1.224
(V)
1.2235
1.223
LT
1.2225
T V
1.222
1.2215
1.221
1.2205
1.22
0 5 10 15 20 25
AP6508
Document number: DS33437 Rev. 5 - 2
INPUT VOLTAGE (V)
V Regulator Li ne Re gu l a t ion
C
INPUT VOLTAGE (V)
Line Regulation vs. Output Current
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