ACE ACE721C

ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Description
The ACE721C is a high-efficiency, DC-to-DC step-down switching regulators, capable of delivering up to
1.2A of output current. The device operates from an input voltage range of 2.6V to 7.0V and provides an
output voltage from 0.6V to VIN, making the ACE721C ideal for low voltage power conversions. Running
at a fixed frequency of 1.5MHz allows the use of small external components, such as ceramic input and
output caps, as well as small inductors, while still providing low output ripples. This low noise output along
with its excellent efficiency achieved by the internal synchronous rectifier, making ACE721C an ideal
green replacement for large power consuming linear regulators. Internal soft-start control circuitry reduces
inrush current. Short-circuit and thermal-overload protection improves design reliability.
Features
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High Efficiency: up to 95%
Capable of Delivering 1.2A
1.5MHz Switching Frequency
No External Schottky Diode Needed
Low dropout 100% Duty operation
Internal Compensation and Soft-Start
Current Mode control
0.6V Reference for Low Output Voltages
Logic Control Shutdown (IQ<1uA)
Thermal shutdown and UVLO
Application
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Cellular phones
Digital Cameras
MP3 and MP4 players
Set top boxes
Wireless and DSL Modems
USB supplied Devices in Notebooks
Portable Devices
VER 1.3
1
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Absolute Maximum Ratings
Parameter
Symbol
Value
Unit
Max Input Voltage
VIN
7
V
Storage Temperature
TS
-40~150
℃
Max Power Dissipation
SOT-23-5
400
mW
Ambient Temperature
TA
-40~85
℃
Max Operating Junction Temperature
TJ
125
℃
>2000
V
-65 to 150
℃
ESD (HBM)
Storage Temperature
TSTG
Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect device reliability.
Packaging Type
5
4
1
2
3
SOT-23-5
Description
1
EN
2
GND
3
SW
4
VIN
5
FB
Function
Enable pin for the IC. Drive the pin to high to enable the part,
and low to disable
Ground
Inductor connection. Connect an inductor between SW and
The regulator output
Supply voltage
Feedback input. Connect and external resistor divider from the
output to FB and GND to set the output to a voltage between
0.6V and Vin
VER 1.3
2
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Ordering information
ACE721C XX XX + H
Halogen - free
Pb - free
BN : SOT-23-5
ADJ: Adjustable Voltage
Functional Block Diagram
Recommended Work Conditions
Item
Max
Unit
Input Voltage Range
5.5
V
Operating Junction Temperature (TJ) -20~125
℃
VER 1.3
3
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Electrical Characteristics
VIN=VEN=3.6V, TA=25℃
Symbol
Parameter
VDD
Input Voltage Range
2.6
Vref
Feedback Voltage
Feedback Leakage
current
0.585
Ifb
Conditions
Min
Active, Vfb=0.65, No Switching
Typ
Max
Unit
7.0
V
0.6
0.612
V
0.1
0.4
uA
35
80
uA
1
uA
Iq
Quiescent Current
LnReg
Line Regulation
Vin=2.7V to 5.5V
0.04
0.2
%/V
LdReg
Load Regulation
Iout=0.01 to 1A
0.1
0.2
Fsoc
Switching Frequency
1.5
%/A
MHz
RdsonP
PMOS Rdson
300
400
mohm
RdsonN
NMOS Rdson
220
300
mohm
Ilimit
Peak Current Limit
1.5
2
A
Iswlk
SW Leakage Current
10
Ienlk
EN Leakage Current
uA
uA
Vh_en
EN Input High Voltage
Vl_en
EN Input Low Voltage
Shutdown
1.2
Vout=5.5V, VSW=0 or 5.5V,
EN=0V
1
1.5
V
0.4
V
Typical Application Circuit
Vin 2.6V to 7.0V
IN
Vout 1.8V/1A
10uF
ACE721C
SW
2.2uH
240K
FB
GND
10uF
120K
1.8V/1A Step-down converter
VER 1.3
4
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Electrical Performance
Tested under TA=25℃, unless otherwise specified
Efficiency VS Load Current
Vout=1.8V
Load Current (mA)
Efficiency VS Load Current
Vout=1.2V
Load Current (mA)
Output Ripple and SW at no load
Vin=5V/Vout=2.5V
Efficiency VS Load Current
Vout=2.5V
Load Current (mA)
Vfb VS Temperature
Temperature (℃)
Output Ripple and SW at 1A load
Vin=5V/Vout=2.5V
VER 1.3
5
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Detailed Description
The ACE721C high-efficiency switching regulator is a small, simple, DC-to-DC step-down converter
capable of delivering up to 1A of output current. The device operates in pulse-width modulation (PWM) at
1.5MHz from a 2.6V to 5.5V input voltage and provides an output voltage from 0.6V to VIN, making the
ACE721C ideal for on-board post-regulation applications. An internal synchronous rectifier improves
efficiency and eliminates the typical Schottky free-wheeling diode. Using the on resistance of the internal
high-side MOSFET to sense switching currents eliminates current-sense resistors, further improving
efficiency and cost.
Load Operation
ACE721C uses a PWM current-mode control scheme. An open-loop comparator compares the
integrated voltage-feedback signal against the sum of the amplified current-sense signal and the slope
compensation ramp. At each rising edge of the internal clock, the internal high-side MOSFET turns on
until the PWM comparator terminates the on cycle. During this on-time, current ramps up through the
inductor, sourcing current to the output and storing energy in the inductor. The current mode feedback
system regulates the peak inductor current as a function of the output voltage error signal. During the off
cycle, the internal high-side P-channel MOSFET turns off, and the internal low-side N-channel MOSFET
turns on. The inductor releases the stored energy as its current ramps down while still providing current to
the output.
Current Sense
An internal current-sense amplifier senses the current through the high-side MOSFET during on time
and produces a proportional current signal, which is used to sum with the slope compensation signal. The
summed signal then is compared with the error amplifier output by the PWM comparator to terminate the
on cycle.
Current Limit
There is a cycle-by-cycle current limit on the high-side MOSFET of 1.5A(typ). When the current flowing
out of SW exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on.
ACE721C utilizes a frequency fold-back mode to prevent overheating during short-circuit output
conditions. The device enters frequency fold-back mode when the FB voltage drops below 200mV,
limiting the current to 1.5A (typ) and reducing power dissipation. Normal operation resumes upon
removal of the short-circuit condition.
Soft-start
ACE721C has a internal soft-start circuitry to reduce supply inrush current during startup conditions.
When the device exits under-voltage lockout (UVLO), shutdown mode, or restarts following a
thermal-overload event, the l soft-start circuitry slowly ramps up current available at SW.
VER 1.3
6
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
UVLO and Thermal Shutdown
If IN drops below 2.5V, the UVLO circuit inhibits switching. Once IN rises above 2.6V, the UVLO clears,
and the soft-start sequence activates. Thermal-overload protection limits total power dissipation in the
device. When the junction temperature exceeds TJ= +160°C, a thermal sensor forces the device into
shutdown, allowing the die to cool. The thermal sensor turns the device on again after the junction
temperature cools by 15°C, resulting in a pulsed output during continuous overload conditions. Following
a thermal-shutdown condition, the soft-start sequence begins.
Design Procedure
Setting Output Voltages
Output voltages are set by external resistors. The FB_ threshold is 0.6V.
RTOP = RBOTTOM[(VOUT / 0.6) - 1]
Input Capacitor Selection
The input capacitor in a DC-to-DC converter reduces current peaks drawn from the battery or other input
power source and reduces switching noise in the controller. The impedance of the input capacitor at the
switching frequency should be less than that of the input source so high-frequency switching currents do
not pass through the input source. The output capacitor keeps output ripple small and ensures
control-loop stability. The output capacitor must also have low impedance at the switching frequency.
Ceramic, polymer, and tantalum capacitors are suitable, with ceramic exhibiting the lowest ESR and
high-frequency impedance. Output ripple with a ceramic output capacitor is approximately as follows:
VRIPPLE = IL(PEAK)[1 / (2π x fOSC x COUT)] If the capacitor has significant ESR, the output ripple
component due to capacitor ESR is as follows: VRIPPLE(ESR) = IL(PEAK) x ESR
Application Information
Layout is critical to achieve clean and stable operation. The switching power stage requires particular
attention. Follow these guidelines for good PC board layout:
1) Place decoupling capacitors as close to the IC as possible
2) Connect input and output capacitors to the same power ground node with a star ground configuration
then to IC ground.
3) Keep the high-current paths as short and wide as possible. Keep the path of switching current (C1 to
IN and C1 to GND) short. Avoid vias in the switching paths.
4) If possible, connect IN, SW, and GND separately to a large copper area to help cool the IC to further
improve efficiency and long-term reliability.
5) Ensure all feedback connections are short and direct. Place the feedback resistors as close to the IC
as possible.
6) Route high-speed switching nodes away from sensitive analog areas
VER 1.3
7
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Packing Information
SOT-23-5
VER 1.3
8
ACE721C
1.2A 1.5MHz 7V Synchronous Buck Converter
Notes
ACE does not assume any responsibility for use as critical components in life support devices or systems
without the express written approval of the president and general counsel of ACE Electronics Co., LTD.
As sued herein:
1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and shoes failure to perform when properly used in
accordance with instructions for use provided in the labeling, can be reasonably expected to result in
a significant injury to the user.
2. A critical component is any component of a life support device or system whose failure to perform can
be reasonably expected to cause the failure of the life support device or system, or to affect its safety
or effectiveness.
ACE Technology Co., LTD.
http://www.ace-ele.com/
VER 1.3
9