AP5100

AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Description
Pin Assignments
The AP5100 is a current mode step-down converter with a
built-in power MOSFET to enable smallest solution size
power conversion.
( Top View )
With the low series resistance power switch it enables a
constant output current of up to 1.2A over a wide input supply
range. The load and line regulation has excellent response
time over the operating input voltage and temperature range.
BST
1
6
SW
GND
2
5
IN
FB
3
74
EN
The AP5100 is self protected, through a cycle-by-cycle
current limiting algorithm and an on chip thermal protection.
SOT26
The AP5100 will provide the voltage conversion with a low
count of widely available standard external components.
The AP5100 is available in SOT26 package.
Features
•
•
•
•
•
•
•
•
•
•
•
•
Applications
VIN 4.75V to 24V
Load current of up to 1.2A
Internal Power MOSFET
Stable with Low ESR Ceramic Output Capacitors
Up to 90% Efficiency
0.1µA Shutdown Mode
Fixed 1.4MHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Resistor divider adjustable Output: 0.81V to 15V
SOT26: Available in “Green” Molding Compound
(No Br, Sb)
Lead Free Finish/RoHS Compliant (Note 1)
Notes:
•
•
•
•
Distributed Power Systems
Battery Charger
Pre-Regulator for Linear Regulators
WLED Drivers
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
VIN = 12V
L = 3.3µH
5
VIN
VOUT = 5V
90
BST 1
IN
EFFICIENCY (%)
C1
C3
VOUT = 3.3V
80
AP5100
SW
.L1
6
VOUT
D1
R1
70
ON
OFF
60
4
EN
GND
FB 3
C6
C2
R2
50
40
0
0.2
0.4
0.6
0.8
1.0
LOAD CURRENT (A)
Fig. 1 Efficiency vs. Load Current
AP5100
Document number: DS32130 Rev. 3 - 2
1.2
Figure 2. Typical Application Circuit
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Typical Application Circuit (cont.)
5
VIN
C1
10µF
25V
BST 1
IN
R3
100kohm
AP5100 SW
4
OFF ON
EN
GND FB
C3
22nF
L1
3.3µH
6
D1
B230A
R1
49.9kohm
3
VOUT
3.3V
C6
100pF
R2
16.2kohm
C2
22µF
6.3V
Figure 3. 1.4MHz, 3.3V Output at 1A Step-Down Converter
5
VIN
BST 1
IN
6V -12V
C1
10µF
25V
R3
100Kohm
AP5100 SW
6
C3
10nF
D1
L1
10µH
1N5819HW-7
- Vout
OFF ON
4
EN
- Vout
GND FB
- Vout
C2
10µF
16V
LED1
LED 2
3
R4
200Kohm
1%
R2
40 ohm
1%
LED 3
- Vout
Figure 4. White LED Driver Application
AP5100
Document number: DS32130 Rev. 3 - 2
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Pin Descriptions
Pin Name
Pin #
Description
BST
1
Bootstrap. To form a boost circuit, a capacitor is connected between SW and BST pins to form a
floating supply across the power switch driver. This capacitor is needed to drive the power switch’s
gate above the supply voltage. Typical values for CBST range from 0.1µF to 1µF.
GND
2
Ground. This pin is the voltage reference for the regulated output voltage. All control circuits are
referenced to this pin. For this reason care must be taken in its layout.
FB
3
Feedback. To set the output voltage, connect this pin to the output resistor divider or directly to
VOUT. To prevent current limit run away during a current limit condition, the frequency foldback
comparator lowers the oscillator frequency when the FB voltage is below 400mV.
EN
4
On/Off Control Input. Do not leave this pin floating. To turn the device ON, pull EN above 1.2V and
to turn it off pull below 0.4V.
If enable/disable is not used, connect a 100kΩ resistor between EN to VIN.
IN
5
Supply Voltage. The AP5100 operates from a +4.75V to +24V unregulated input. A decoupling
capacitor C1 is required to prevent large voltage spikes from appearing at the input. Place this
capacitor near the IC.
SW
6
Switch Output. This is the reference for the floating top gate driver.
Functional Block Diagram
Σ
Figure 5. Functional Block Diagram
AP5100
Document number: DS32130 Rev. 3 - 2
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Absolute Maximum Ratings (Note 2)
Symbol
Description
ESD HBM
Human Body Model ESD Protection
ESD MM
Unit
3
KV
Machine Model ESD Protection
300
V
VIN
Supply Voltage
26
V
VSW
Switch Voltage
-0.3 to VIN +0.3
V
VBST
Boost Voltage
VSW +6
V
All Other Pins
Notes:
Rating
–0.3 to +6
V
TST
Storage Temperature
-65 to +150
°C
TJ
Junction Temperature
+150
°C
TL
Lead Temperature
+260
°C
θJA
Junction to Ambient Thermal Resistance (Note 3)
140
°C/W
θJC
Junction to Case Thermal Resistance (Note 3)
35
°C/W
2. Exceeding these ratings may damage the device.
3. Test condition for SOT26: Measured on approximately 1” square of 1 oz copper.
Recommended Operating Conditions (Note 4)
Symbol
Rating
Unit
VIN
Supply Voltage
4.75 to 24
°C
TA
Operating Ambient Temperature Range
-25 to +85
°C
Output Voltage
0.81 to 15
V
VOUT
Note:
Description
4. The device function is not guaranteed outside of the recommended operating conditions.
AP5100
Document number: DS32130 Rev. 3 - 2
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Electrical Characteristics (VIN = 12V, TA = +25°C, unless otherwise noted)
Symbol
Parameter
Test Conditions
VFB
Feedback Voltage
4.75V ≤ VIN ≤ 24V
IFB
Feedback Current
VFB = 0.8V
RDS(ON)
Min
Typ.
Max
Unit
0.790
0.810
0.830
V
Switch-On Resistance (Note 5)
Switch Leakage
tON
µA
0.35
Ω
VEN = 0V, VSW = 0V
10
Current Limit (Note 5)
fSW
0.1
2.4
A
Oscillator Frequency
VFB = 0.6V
Fold-back Frequency
VFB = 0V
480
kHz
Maximum Duty Cycle
VFB = 0.6V
87
%
100
ns
1.1
Minimum On-Time (Note 5)
Under Voltage Lockout Threshold
Rising
3.8
Under Voltage Lockout Threshold
Hysteresis
1.4
4.0
4.2
MHz
V
mV
0.4
EN Input High Voltage
EN Input Current
1.7
150
EN Input Low Voltage
1.2
V
V
VEN = 2V
0.3
VEN = 0V
0.1
µA
IS
Supply Current (Shutdown)
VEN = 0V
0.1
1.0
µA
IQ
Supply Current (Quiescent)
VEN = 2V, VFB = 1V
0.4
1.0
mA
Thermal Shutdown (Note 5)
Note:
µA
140
°C
5. Guaranteed by design.
AP5100
Document number: DS32130 Rev. 3 - 2
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AP
P5100
1.2A STE
EP-DOWN CONVERT
C
TER with 1.4MHz SWITCHING
FREQ
QUENCY
Typical Pe
erformance
e Characte
eristics
VIN = 12V, VOU
3
C1 = 10
0µF, C2 = 22µF
F, TA = +25°C, unless otherw
wise noted.
UT = 3.3V, L = 3.3µH,
Stead
dy State Test
(IOUT = 0.5A)
Lo
oad Transientt Test
(IOUT = 0.2
2A to 0.8A. Ste
ep at 0.8A/µs)
Tim
me- 1µs/div
Time- 100µs/d
div
Start-up Through
T
Enab
ble
(N
No Load)
Starrt-up through Enable
(IOUTT = 1A, resistiv
ve load)
Time- 50µs/div
Time- 50µs/d
div
Shutdown
n Through Ena
able
(N
No Load)
Shutd
down Through
h Enable
(IOUTT = 1A, resistiv
ve load)
Time- 50µs/div
Time- 50µs/d
div
AP5100
Document numberr: DS32130 Rev. 3 - 2
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m
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odes Incorporated
AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Typical Performance Characteristics (cont.)
Short Circuit Entry
Short Circuit Recovery
Time- 50µs/div
Time- 100µs/div
Applications Information
OPERATION
Setting the Output Voltage
The AP5100 is a current mode control, asynchronous buck
regulator. Current mode control assures excellent line and
load regulation and a wide loop bandwidth for fast
response to load transients. Figure. 4 depicts the
functional block diagram of AP5100.
The output voltage can be adjusted from 0.81V to 15V
using an external resistor divider. Table 1 shows a list of
resistor selection for common output voltages. Resistor
R1 is selected based on a design tradeoff between
efficiency and output voltage accuracy. For high values of
R1 there is less current consumption in the feedback
network. However the trade off is output voltage accuracy
due to the bias current in the error amplifier. R2 can be
determined by the following equation:
The operation of one switching cycle can be explained as
follows. At the beginning of each cycle, HS (high-side)
MOSFET is off. The EA output voltage is higher than the
current sense amplifier output, and the current
comparator’s output is low. The rising edge of the 1.4MHz
oscillator clock signal sets the RS Flip-Flop. Its output
turns on HS MOSFET.
⎛V
⎞
R1 = R 2 × ⎜⎜ OUT − 1⎟⎟
0.81
⎝
⎠
Equation 1
When the HS MOSFET is on, inductor current starts to
increase. The Current Sense Amplifier senses and
amplifies the inductor current. Since the current mode
control is subject to sub-harmonic oscillations that peak at
half the switching frequency, Ramp slope compensation is
utilized. This will help to stabilize the power supply. This
Ramp compensation is summed to the Current Sense
Amplifier output and compared to the Error Amplifier
output by the PWM Comparator. When the sum of the
Current Sense Amplifier output and the Slope
Compensation signal exceeds the EA output voltage, the
RS Flip-Flop is reset and HS MOSFET is turned off. The
external Schottky rectifier diode (D1) conducts the inductor
current.
For one whole cycle, if the sum of the Current Sense
Amplifier output and the Slope Compensation signal does
not exceed the EA output, then the falling edge of the
oscillator clock resets the Flip-Flop. The output of the
Error Amplifier increases when feedback voltage (VFB) is
lower than the reference voltage of 0.81V. This also
increases the inductor current as it is proportional to the
EA voltage.
AP5100
Document number: DS32130 Rev. 3 - 2
VOUT (V)
1.8
2.5
3.3
5
R1 (kΩ)
80.6 (1%)
49.9 (1%)
49.9 (1%)
49.9 (1%)
R2 (kΩ)
64.9 (1%)
23.7 (1%)
16.2 (1%)
9.53 (1%)
Table 1. Resistor Selection for Common
Output Voltages
L=
VOUT × (VIN − VOUT )
VIN × ΔIL × fSW
Equation 2
Where ΔIL is the inductor ripple current.
And fSW is the buck converter switching frequency.
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Applications Information (cont.)
Setting the Output Voltage (cont.)
Choose the inductor ripple current to be 30% of the
maximum load current. The maximum inductor peak
current is calculated from:
ΔI
IL(MAX) = ILOAD + L
2
Equation 3
Peak current determines the required saturation current
rating, which influences the size of the inductor. Saturating
the inductor decreases the converter efficiency while
increasing the temperatures of the inductor, the MOSFET
and the diode. Hence choosing an inductor with
appropriate saturation current rating is important.
A 1µH to 10µH inductor with a DC current rating of at least
25% percent higher than the maximum load current is
recommended for most applications.
For highest efficiency, the inductor’s DC resistance should
be less than 200mΩ.
Use a larger inductance for
improved efficiency under light load conditions.
Input Capacitor
The input capacitor reduces the surge current drawn from
the input supply and the switching noise from the device.
The input capacitor has to sustain the ripple current
produced during the on time on the upper MOSFET. It
must hence have a low ESR to minimize the losses.
Due to large dI/dt through the input capacitors, electrolytic
or ceramics should be used. If a tantalum must be used, it
must be surge protected. Otherwise, capacitor failure
could occur. For most applications, a 4.7µF ceramic
capacitor is sufficient.
ESR of the output capacitor dominates the output voltage
ripple. The amount of ripple can be calculated from the
equation below:
Vout capacitor = ΔIinductor × ESR
An output capacitor with ample capacitance and low ESR
is the best option. For most applications, a 22µF ceramic
capacitor will be sufficient.
External Diode
The external diode’s forward current must not exceed the
maximum output current. Since power dissipation is a
critical factor when choosing a diode, it can be calculated
from the equation below:
V
Pdiode = (1 − OUT ) × Iout × 0.3V
VIN
Equation 5
Note: 0.3V is the voltage drop across the schottky diode. A
diode that can withstand this power dissipation must be
chosen.
External Bootstrap Diode
It is recommended that an external bootstrap diode be
added when the input voltage is no greater than 5V or the
5V rail is available in the system. This helps improve the
efficiency of the regulator. The bootstrap diode can be a
low cost one such as IN4148 or BAT54.
5V
Output Capacitor
The output capacitor keeps the output voltage ripple small,
ensures feedback loop stability and reduces the overshoot
of the output voltage. The output capacitor is a basic
component for the fast response of the power supply. In
fact, during load transient, for the first few microseconds it
supplies the current to the load. The converter recognizes
the load transient and sets the duty cycle to maximum, but
the current slope is limited by the inductor value.
Maximum capacitance required can be calculated from the
following equation:
ΔI
L(IOUT + inductor ) 2
2
Co =
(Δ V + VOUT ) 2 − VOUT 2
Equation 4
Where ΔV is the maximum output voltage overshoot.
Where ΔIinductor is the inductor ripple current.
AP5100
Document number: DS32130 Rev. 3 - 2
BST
1
AP5100
BOOST
DIODE
10nF
SW
6
Figure 6. External Bootstrap Diode
Under Voltage Lockout (UVLO)
Under Voltage Lockout is implemented to prevent the IC
malfunction from insufficient input voltages. For power-up,
the AP5100 must be enabled and the input voltage must
be higher than the UVLO rising threshold (4.0 V typ).
When the input voltage falls below the UVLO falling
threshold (UVLO rising threshold – UVLO hysteresis), the
AP5100 will latch an under voltage fault. In this event, the
output will fall low. To resume normal operation, the
AP5100 must be pulled above the UVLO rising threshold.
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Applications Information (cont.)
Internal Soft Start
Thermal Shutdown
Soft start is traditionally implemented to prevent the
excess inrush current. This in turn prevents the converter
output voltage from overshooting when it reaches
regulation. The AP5100 has an internal current source
with a soft start capacitor to ramp the reference voltage
from 0V to 0.810V. The soft start time is internally fixed at
200us (TYP). The soft start sequence is reset when there
is a Thermal Shutdown, Under Voltage Lockout (UVLO) or
when the part is disabled using the EN pin.
The AP5100 has on-chip thermal protection that prevents
damage to the IC when the die temperature exceeds safe
margins. It implements a thermal sensing to monitor the
operating junction temperature of the IC. Once the die
temperature rises to approximately 140°C, the thermal
protection feature gets activated .The internal thermal
sense circuitry turns the IC off thus preventing the power
switch from damage.
A hysteresis in the thermal sense circuit allows the device
to cool down to approximately 120°C before the IC is
enabled again. This thermal hysteresis feature prevents
undesirable oscillations of the thermal protection circuit.
Current Limit
The AP5100 has cycle-by-cycle current limiting
implementation. The voltage drop across the internal highside mosfet is sensed and compared with the internally set
current limit threshold. This voltage drop is sensed at
about 30ns after the HS turns on. When the peak inductor
current exceeds the set current limit threshold, current limit
protection is activated. During this time the feedback
voltage (VFB) drops down. When the voltage at the FB pin
reaches 0.4V, the internal oscillator shifts the frequency
from the normal operating frequency of 1.4MHz to a foldback frequency of 480kHz. The current limit is reduced to
70% of nominal current limit when the part is operating at
480kHz. This low Fold-back frequency prevents runaway
current.
AP5100
Document number: DS32130 Rev. 3 - 2
PC Board Layout
This is a high switching frequency converter. Hence
attention must be paid to the switching currents
interference in the layout. Switching current from one
power device to another can generate voltage transients
across the impedances of the interconnecting bond wires
and circuit traces. These interconnecting impedances
should be minimized by using wide, short printed circuit
traces. The input capacitor needs to be as close as
possible to the IN and GND pins. The external feedback
resistors should be placed next to the FB pin.
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Ordering Information
AP5100 W G - 7
Package
Green
Packing
W : SOT26
G : Green
7 : Tape & Reel
13” Tape and Reel
Device
Package
Code
Packaging
(Note 6)
Quantity
Part Number Suffix
AP5100WG-7
W
SOT26
3000/Tape & Reel
-7
Note:
6. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at
http://www.diodes.com/datasheets/ap02001.pdf.
Marking Information
SOT26
( Top View )
5
4
7
6
XX Y W X
1
AP5100
Document number: DS32130 Rev. 3 - 2
2
3
XX : Identification Code
Y : Year 0~9
W : Week : A~Z : 1~26 week;
a~z : 27~52 week; z represents
52 and 53 week
X : A~Z : Green
Part Number
Package
Identification Code
AP5100W
SOT26
AJ
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
Package Outline Dimensions (All Dimensions in mm)
SOT26
A
SOT26
Dim Min Max Typ
A
0.35 0.50 0.38
B
1.50 1.70 1.60
C
2.70 3.00 2.80
D
⎯
⎯ 0.95
H
2.90 3.10 3.00
J
0.013 0.10 0.05
K
1.00 1.30 1.10
L
0.35 0.55 0.40
M
0.10 0.20 0.15
0°
8°
α
⎯
All Dimensions in mm
B C
H
K
M
J
L
D
Suggested Pad Layout
SOT26
C2
Z
C2
Dimensions Value (in mm)
Z
3.20
G
1.60
X
0.55
Y
0.80
C1
G
C1
C2
Y
2.40
0.95
X
AP5100
Document number: DS32130 Rev. 3 - 2
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AP5100
1.2A STEP-DOWN CONVERTER with 1.4MHz SWITCHING
FREQUENCY
IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS
DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
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LIFE SUPPORT
Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without
the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided
in the labeling can be reasonably expected to result in significant injury to the user.
B.
A critical component is any component in a life support device or system whose failure to perform can be reasonably expected
to cause the failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or
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concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems,
notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further,
Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes
Incorporated products in such safety-critical, life support devices or systems.
Copyright © 2012, Diodes Incorporated
www.diodes.com
AP5100
Document number: DS32130 Rev. 3 - 2
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