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PDF AP65454 Data sheet ( Hoja de datos )
| Número de pieza | AP65454 | |
| Descripción | 650kHz ADAPTIVE COT STEP-DOWN CONVERTER | |
| Fabricantes | Diodes | |
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AP65454
4A, 18V, 650kHz ADAPTIVE COT STEP-DOWN CONVERTER
Description
The AP65454 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 TVs
and monitors.
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 as well as ultra-low ESR ceramic capacitors.
The AP65454 also features programmable soft-start, UVLO, OTP and
OCP to protect the circuit. This IC is available in SO-8EP package.
Pin Assignments
( Top View )
EN 1
FB 2
VREG5 3
SS 4
8
7
6
5
SO-8EP
VIN
BS
SW
GND
AP65454 operates in continuous conduction mode (CCM) in light-load
conditions for better EMI performance. AP65453 and AP65455 are
the options for light-load efficiency enhancement.
Features
Fixed Frequency Emulated Constant On-Time Control
Good Stability Independent of the Output Capacitor ESR
Fast Load Transient Response
Synchronous Rectification: 90mΩ Internal High-Side Switch and
57mΩ 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 Overcurrent 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)
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
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.
AP65454
Document number: DS38483 Rev. 1 - 2
1 of 13
www.diodes.com
December 2015
© Diodes Incorporated
1 page  
AP65454
Typical Performance Characteristics (@TA = +25°C, VIN = 12V, VOUT = 1.05V, unless otherwise specified.)
85˚C
25˚C
-40˚C
-40˚C
85˚C
25˚C
VIN=18V
VIN=12V
VIN=4.5V
IO=0mA
IO=1A
AP65454
Document number: DS38483 Rev. 1 - 2
5 of 13
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December 2015
© Diodes Incorporated
5 Page 
AP65454
Application Information (cont.)
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 Vout)2 Vout2
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.
External Bootstrap Diode
It is recommended to add an external bootstrap diode between an external 5V and the BS pin for efficiency improvement when input voltage is
lower than 5.5V. The bootstrap diode can be a low cost one such as 1N4148 or BAT54. The external 5V can be a 5V fixed input from system or a
5V output of the AP65454. Note that the external bootstrap voltage must be lower than 5.5V.
Figure 6 External Bootstrap Diode
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 AP65454 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.
AP65454
Document number: DS38483 Rev. 1 - 2
Figure 7 PC Board Layout
11 of 13
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December 2015
© Diodes Incorporated
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| PDF Descargar | [ Datasheet AP65454.PDF ] | |
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