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PDF AP65450 Data sheet ( Hoja de datos )
| Número de pieza | AP65450 | |
| Descripción | 650kHz ADAPTIVE COT STEP-DOWN CONVERTER | |
| Fabricantes | Diodes | |
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AP65450
4A, 18V, 650kHz ADAPTIVE COT STEP-DOWN CONVERTER
Description
The AP65450 is an adaptive constant on-time mode synchronous
buck converter providing high efficiency, excellent transient response
and high DC output accuracy for low-voltage regulation in digital TV
and monitor.
The constant-on-time control scheme handles wide input/output
voltage ratios and provides low external component count. The
internal proprietary circuit enables the device to adopt both low
equivalent series resistance (ESR) output capacitors, such as
SP-CAP or POSCAP and ultra-low ESR ceramic capacitors.
The adaptive on-time control supports seamless transition between
continuous conduction mode (CCM) at higher load conditions and
discontinuous conduction mode (DCM) at lighter load conditions.
DCM allows AP65450 to maintain high efficiency at light load
conditions. The AP65450 also features programmable soft-start,
UVLO, OTP and OCP to protect the circuit.
This IC is available in SO-8EP package.
Features
Fixed Frequency Emulated Constant On-time Control
Good Stability Independent of the Output Capacitor ESR
Fast Load Transient Response
Synchronous Rectification: 65mΩ Internal High-side Switch and
36mΩ Internal Low-side Switch
Wide Input Voltage Range: 4.5V to 18V
Output Voltage Range: 0.76V to 6V
4A Continuous Output Current
650kHz Switching Frequency
Built-in Over Current Limit
Built-in Thermal Shutdown Protection
Programmable Soft-start
Pre-biased Start-up
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Pin Assignments
( Top View )
EN 1
FB 2
VREG5 3
SS 4
8
7
6
5
SO-8EP
Applications
Gaming Consoles
Flat Screen TV Sets and Monitors
Set-Top Boxes
Distributed power systems
Home Audio
Consumer Electronics
Network Systems
FPGA, DSP and ASIC Supplies
Green Electronics
VIN
BS
SW
GND
Notes:
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 Applications Circuit
INPUT
VIN
12V
C1
20μF
87
IN BST
OFF
C4
8.2nF
ON 1
EN
4
SS
6
SW
AP65450
2
FB
3
5 VREG5
GND
C5 L1
0.1µF 1.5μH
R1
8.25kΩ
R2
22.1kΩ
C3
1µF
OUTPUT
VOUT
1.05V
C2
44μF
Figure 1 Typical Application Circuit
AP65450
Document number: DS37135 Rev. 2-2
1 of 14
www.diodes.com
November 2014
© Diodes Incorporated
1 page  
AP65450
Typical Performance Characteristics (@TA = +25°C, VIN = 12V, VOUT = 3.3V, unless otherwise specified.)
85˚C
25˚C
-40˚C
-40˚C
25˚C
85˚C
VIN=18V
VIN=12V
VIN=4.5V
IO=10mA
IO=1A
AP65450
Document number: DS37135 Rev. 2-2
5 of 14
www.diodes.com
November 2014
© Diodes Incorporated
5 Page 
AP65450
Application Information (cont.)
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 have a low ESR to minimize the losses.
The RMS current rating of the input capacitor is a critical parameter that must be higher than the RMS input current. As a rule of thumb, select an
input capacitor which has an RMs rating that is greater than half of the maximum load current.
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, greater than 10µF ceramic capacitor is sufficient.
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:
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 to 68µF ceramic capacitor will be
sufficient.
Co
L(Iout
ΔIin d u cto r ) 2
2
(Δ
V
Vo u t ) 2
Vo
u
2
t
Where ΔV is the maximum output voltage overshoot.
Bootstrap Capacitor
To ensure the proper operation, a ceramic capacitor must be connected between the VBST and SW pin. A 0.1µF ceramic capacitor is sufficient.
VREG5 Capacitor
To ensure the proper operation, a ceramic capacitor must be connected between the VREG5 and GND pin. A 1µF ceramic capacitor is sufficient.
.
PC Board Layout
1. The AP65450 works at 4A load current, heat dissipation is a major concern in layout the PCB. A 2oz Copper in both top and bottom
layer is recommended.
2. Provide sufficient vias in the thermal exposed pad for heat dissipate to the bottom layer.
3. Provide sufficient vias in the Output capacitor GND side to dissipate heat to the bottom layer.
4. Make the bottom layer under the device as GND layer for heat dissipation. The GND layer should be as large as possible to provide
better thermal effect.
5. Make the Vin capacitors as close to the device as possible.
6. Make the VREG5 capacitor as close to the device as possible.
7. The thermal pad of the device should be soldered directly to the PCB exposed copper plane to work as a heatsink. The thermal vias in
the exposed copper plane increase the heat transfer to the bottom layer.
AP65450
Document number: DS37135 Rev. 2-2
11 of 14
www.diodes.com
November 2014
© Diodes Incorporated
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet AP65450.PDF ] | |
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