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AP5101SG-13

P1-P3P4-P6P7-P9P10-P12P13-P15
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
AP5101
Document number: DS32258 Rev. 1 - 2
7 of 15
www.diodes.com
July 2010
© Diodes Incorporated
NEW PRODUCT
Typical Performance Characteristics (continued)
V
IN
=12V, V
OUT
=3.3V, L =4.7uH, C1=10uF, C2=22uF, Ta=+25
•
C, unless otherwise noted.
Short Circuit Entry
Time- 50us/div
Short Circuit Recovery
Time- 100us/div
Current Sense Transconductance (Gcs)
Gcs= 1.5A/(comp2-comp1)=1.5A/(1.8-0.65) =1.3A/V
Time- 2us/div
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
AP5101
Document number: DS32258 Rev. 1 - 2
8 of 15
www.diodes.com
July 2010
© Diodes Incorporated
NEW PRODUCT
Applications Information
Operation
The AP5101 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. 3 depicts the functional block diagram of
AP5101.
The operation of one switching 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.
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 switching 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 (V
FB
) is lower than the reference voltage of 0.81V. This also increases the inductor current
as it is proportional to the EA voltage.
REGULATOR
REFERENCE
RAMP
GENERATOR
OSCILLATOR
1.4MHz/500KHz
RSEN
25mO
+
-
CURRENT SENSE AMPLIFIER
R
S
Q
R
DRIVER
REGULATOR
7
1
5
4
3
2
IN
EN
FB
GND
+
-
EA
ERROR AMPLIFIER
+
-
+
-
BST
SW
PWM
COMPARATOR
CURRENT LIMIT
COMPARATOR
6
COMP
8
GND
Figure 3. Functional Block Diagram
AP5101
1.5A Step-Down Converter with 1.4MHz Switching
Frequency
AP5101
Document number: DS32258 Rev. 1 - 2
9 of 15
www.diodes.com
July 2010
© Diodes Incorporated
NEW PRODUCT
Applications Information (Continued)
Component Selection
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:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−×= 1
0.81
OUT
V
2
R
1
R
V
OUT
(V) R
1
(kΩ) R
2
(kΩ)
1.8 80.6 (1%) 64.9 (1%)
2.5 49.9 (1%) 23.7 (1%)
3.3 49.9 (1%) 16.2 (1%)
5.0 49.9 (1%) 9.53 (1%)
Table 1. Resistor Selection for Common Output Voltage
Compensation Components
The AP5101 has an external COMP pin through which system stability and transient response can be controlled. COMP pin is
the output of the internal trans-conductance error amplifier. A series capacitor-resistor combination sets a pole-zero
combination to control the characteristics of the control system. The DC gain of the voltage feedback loop is given by:
OUT
V
FB
V
VEA
A
CS
G
LOAD
R
VDC
A ×××=
Where V
FB
is the feedback voltage (0.810V), R
LOAD
is the load resistor value, G
CS
is the current sense trans-conductance and
A
VEA
is the error amplifier voltage gain.
The control loop transfer function incorporates two poles. One is due to the compensation capacitor (C3) and the output
resistor of error amplifier, and the other is due to the output capacitor and the load resistor. These poles are located at:
VEA
A3C2
EA
G
P1
f
××π
=
LOAD
R2C2
1
P2
f
××π
=
Where G
EA
is the error amplifier trans-conductance.
One zero is present due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at:
3R3C2
1
Z1
f
××π
=
P1-P3P4-P6P7-P9P10-P12P13-P15

AP5101SG-13

Mfr. #:
Buy AP5101SG-13
Manufacturer:
Diodes Incorporated
Description:
Switching Voltage Regulators 1.5A Step-Down CONV 1.4MHz 4.75 to 22V
Lifecycle:
New from this manufacturer.
Delivery:
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