APS2415

 

Synchronous Step-Down Converter

 

 

 

Chipown

Chipown



APS2415 Datasheet PDF
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APS2415
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1.2MHz, 1.5A
Synchronous Step-Down Converter
General Description
The APS2415 is a high efficiency monolithic
synchronous buck regulator using a constant frequency,
current mode architecture. The device is available in an
adjustable version and fixed output voltages, such as
1.2V, 1.5V, 1.8V, etc. Supply current with no load is
300uA and drops to <1uA in shutdown. The 2.5V to
6.5V input voltage range makes the APS2415 ideally
suited for single Li-Ion, two to four AA battery-powered
applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
PWM pulse skipping mode operation provides very low
output ripple voltage for noise sensitive applications.
Switching frequency is internally set at 1.2MHz,
allowing the use of small surface mount inductors and
capacitors. The internal synchronous switch increases
efficiency and eliminates the need for an external
Schottky diode. Low output voltages are easily
supported with the 0.6V feedback reference voltage. The
APS2415 is available in a small SOT package.
Applications
z Cellular and Smart Phones
z Microprocessors and DSP Core Supplies
z Wireless and DSL Modems
z PDAs
z MP3 / MP4 /PMP Player
z Digital Still and Video Cameras
z Portable Instruments
Typical Application Circuit
Figure 1. Basic Application Circuit with
APS2415 adjustable version
Features
z High Efficiency: Up to 96%
z 1.2MHz Constant Switching Frequency
z 1.5A Output Current at VIN=3V
z Integrated Main switch and synchronous rectifier.
No Schottky Diode Required
z 2.5V to 6.5V Input Voltage Range
z Output Voltage as Low as 0.6V
z 100% Duty Cycle in Dropout
z Quiescent Current: 300µA(input < 4.2V)
z Slope Compensated Current Mode Control for
Excellent Line and Load Transient Response
z Short Circuit Protection
z <1uA Shutdown Current
z Soft start
z Space Saving 5-Pin SOT23 package
Package
SOT23-5L
100
95
90
85
80
75
70
65
60
55
50
0
η vs Io(Vo=1.8V)
Vin=2.5V
Vin=3.6V
Vin=4.2V
Vin=5V
Vin=6V
300 600 900 1200 1500
Io(mA)
Figure 2. Typical Efficiency Curve
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APS2415
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Pin Description
Pin Pin Pin Function
No. Name
Regulator Enable control input. Drive RUN above 1.5V to turn on the part. Drive RUN
1 RUN below 0.6V to turn it off. In shutdown, all functions are disabled drawing <1µA supply current.
Do not leave RUN floating.
2 GND Ground.
3
SW
Power Switch Output. It is the Switch note connection to Inductor. This pin connects to the
drains of the internal P-CH and N-CH MOSFET switches.
4
VIN
Supply Input Pin. Must be closely decoupled to GND, Pin 2, with a 22µF or greater ceramic
capacitor.
VFB (APS2415): Feedback Input Pin. Connect FB to the center point of the external resistor
5
VFB/ divider. The feedback threshold voltage is 0.6V.
VOUT VOUT (APS2415-1.2/APS2415-1.8): Output Voltage Feedback Pin. An internal resistive divider
divides the output voltage down for comparison to the internal reference voltage.
Functional Block Diagram
Figure 3. APS2415 Block Diagram
(Note 1)
Absolute Maximum Rating
Input Supply Voltage.......................................................................................................................................-0.3V to +7V
RUN, V Voltages................................................................................................................................-0.3V to V +0.3V
FB IN
SW Voltages............................................................................................................................................-0.3V to V +0.3V
IN
(Note 2)
Package Thermal Resistance
Ө ...............................................................................................................................................................220°C/W
JA
Ө ...............................................................................................................................................................110°C/W
JC
Operating Temperature Range.....................................................................................................................-40°C to +85°C
(Note 3)
Junction Temperature
.....................................................................................................................................+125°C
Storage Temperature Range.......................................................................................................................-65°C to +150°C
Lead Temperature (Soldering, 10s)..........................................................................................................................+260°C
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APS2415
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(Note 4)
Electrical Characteristics
(V =V = 3.6V, TA = 25°C, unless otherwise noted.)
IN RUN
Parameter
Input Voltage Range
Conditions
Min Typ Max unit
2.5 6.5 V
Input DC Supply Current
Active Mode
Shutdown Mode
Regulated Feedback Voltage
V Input Bias Current
FB
Reference Voltage Line
Regulation
Regulated Output Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
Peak Inductor Current
V =0.5V or V =90%
FB OUT
V =0V, V =4.2V
FB IN
T = +25°C
A
T = 0°C T 85°C
AA
T = -40°C T 85°C
AA
V = 0.65V
FB
V = 2.5V to 5.5V,
IN
Iout=10mA
APS2415-1.2, -40°C T 85°C
A
APS2415-1.8, -40°C T 85°C
A
V = 2.5V to 5.5V
IN
Iout=10mA
Iout=10 to 1500mA
V =3V, V =0.5V or V =90%
IN FB
OUT
Duty Cycle <35%
0.5880
0.5865
0.5820
1.164
1.746
2.5
300
0.1
0.6000
0.6000
0.6000
400
1.0
0.6120
0.6135
0.6180
±30
0.5 0.60
1.200
1.800
1.236
1.854
0.5 0.60
0.5
3.5
µA
µA
V
V
V
nA
%/V
V
V
%/V
%
A
Oscillator Frequency
R of P-CH MOSFET
DS(ON)
R of N-CH MOSFET
DS(ON)
SW Leakage
Soft start
RUN Threshold Low
RUN Threshold High
RUN Leakage Current
V =0.6V or V =100%
FB OUT
I = 300mA
SW
I = -300mA
SW
V = 0V, V = 0V or 5V, V =
RUN
SW
IN
5V
0.96
-40°C T 85°C
A
1.5
1.2 1.44 MHz
135 200 m
95 150 m
±0.01 ±1
µA
1.3
±0.01
0.6
±1
mS
V
µA
Thermal Shutdown
165 °C
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
Note 2: Thermal Resistance is specified with approximately 1 square of 1 oz copper.
Note 3: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following
formula: APS2415: TJ = TA + (PD)x(220°C/W)
Note 4:100% production test at +25°C. Specifications over the temperature range are guaranteed by design and
characterization.
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Typical Performance Characteristics (Test Figure 1 above unless otherwise specified)
100
95
90
85
80
75
70
65
60
55
50
0
η vs Io(Vo=1.2V)
Vin=2.5V
Vin=3.6V
Vin=4.2V
Vin=5V
Vin=6V
300 600 900 1200 1500
Io(mA)
100
95
90
85
80
75
70
65
60
0
η vs Io(Vo=3.3V)
Vin=4.2V
Vin=5V
Vin=6V
300 600 900 1200 1500
Io(mA)
Ripple(CH1:VIN, CH2:VO, CH3:VSW)
VIN=3.6V,VO=1.8V,IO=0
VIN=3.6V,VO=1.8V,IO=1.5A
Soft Start(CH1:VIN, CH2:VO, CH3:VSW,CH4:ISW)
VIN=3.6V,VO=1.8V,IO=0
VIN=3.6V,VO=1.8V,RL=1.5
Order Information
Part number
APS2415TBER-ADJ
1.XY=date code
P=Package factory
Mark
S1XYP1
P
Package
SOT-23-5L
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APS2415
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Operation
APS2415 is a monolithic switching mode Step-Down
DC-DC converter. It utilizes internal MOSFETs to
achieve high efficiency and can generate very low
output voltage by using internal reference at 0.6V. It
operates at a fixed switching frequency, and uses the
slope compensated current mode architecture. This
Step-Down DC-DC Converter supplies 1500mA output
current at Vout = 1.8V with input voltage range from
2.5V to 6.5V.
Current Mode PWM Control
Slope compensated current mode PWM control provides
stable switching and cycle-by-cycle current limit for
excellent load and line responses and protection of the
internal main switch (P-Ch MOSFET) and synchronous
rectifier (N-CH MOSFET). During normal operation,
the internal P-Ch MOSFET is turned on for a certain
time to ramp the inductor current at each rising edge of
the internal oscillator, and switched off when the peak
inductor current is above the error voltage. The current
comparator, ICOMP, limits the peak inductor current.
When the main switch is off, the synchronous rectifier
will be turned on immediately and stay on until either
the inductor current starts to reverse, as indicated by the
current reversal comparator, IZERO, or the beginning of
the next clock cycle. The OVDET comparator controls
output transient overshoots by turning the main switch
off and keeping it off until the fault is no longer present.
converter decreases. Caution must be exercised to
ensure the heat dissipated not to exceed the maximum
junction temperature of the IC.
Note 5: The duty cycle D of a step-down converter is
defined as:
D
= TON
×
f OSC
×100%
V OUT
VIN
×100%
Where TON is the main switch on time and fOSC is the
oscillator frequency (1.2MHz).
Maximum Load Current
The APS2415 will operate with input supply voltage as
low as 2.5V, however, the maximum load current
decreases at lower input due to large IR drop on the
main switch and synchronous rectifier. The slope
compensation signal reduces the peak inductor current
as a function of the duty cycle to prevent sub-harmonic
oscillations at duty cycles greater than 50%.
Conversely the current limit increases as the duty cycle
decreases.
Layout Guidance
When laying out the PCB board, the following
suggestions should be taken to ensure proper operation
of the APS2415. These items are also illustrated
graphically in Figure 4 & Figure 5.
Idle Mode Operation
At very light loads, the APS2415 automatically enters
pulse skipping Mode. In the pulse skipping Mode, the
inductor current may reach zero or reverse on each pulse.
The PWM control loop will automatically skip pulses to
maintain output regulation. The bottom MOSFET is
turned off by the current reversal comparator, IZERO, and
the switch voltage will ring. This is discontinuous
mode operation, and is normal behavior for the
switching regulator.
Dropout Operation
When the input voltage decreases toward the value of
the output voltage, the APS2415 allows the main switch
to remain on for more than one switching cycle and
increases the duty cycle (Note 5) until it reaches 100%.
The output voltage then is the input voltage minus the
voltage drop across the main switch and the inductor.
At low input supply voltage, the RDS(ON) of the
P-Channel MOSFET increases, and the efficiency of the
1. The power traces, including the GND trace, the SW
trace and the VIN trace should be kept short, direct
and wide.
2. The VFB pin should be connected directly to the
feedback resistor. The resistive divider R1/R2 must
be connected between the (+) plate of Cout and
ground.
3. Connect the (+) plate of C1 to the VIN pin as
closely as possible. This capacitor provides the AC
current to internal power MOSFET.
4. Keep the switching node, SW, away from the
sensitive VFB node.
5. Keep the (-) plates of C1 and C3 as close as
possible.
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Figure4. APS2415 ADJ output Suggested Layout
Figure5. APS2415 Fixed output Suggested Layout
Application Information
Setting the Output Voltage
Figure 1 above shows the basic application circuit with
APS2415 adjustable output version. The external
resistor sets the output voltage according to the
following equation:
VOUT
= 0.6V
× ⎜⎛1 +
R2
R1
⎟⎞
R1=200Kfor all outputs; R2= 200kfor VOUT=1.2V,
R2=300kfor VOUT =1.5V, R2=400kfor VOUT
=1.8V, and R2=633.3kfor VOUT =2.5V.
Inductor Selection
For most designs, the APS2415 operates with inductors
of 1µH to 4.7µH. Low inductance values are physically
smaller but require faster switching, which results in
some efficiency loss. The inductor value can be
derived from the following equation:
( )L = VOUT × VIN VOUT
VIN × ΔI L × fOSC
Where ΔI L is inductor Ripple Current. Large value
inductors lower ripple current and small value inductors
result in high ripple currents. Choose inductor ripple
current approximately 35% of the maximum load
current 1500mA, or ΔI L =525mA.
For output voltages above 2.0V, when light-load
efficiency is important, the minimum recommended
inductor is 2.2µH. For optimum voltage-positioning
load transients, choose an inductor with DC series
resistance in the 50mto 150mrange. For higher
efficiency at heavy loads (above 500mA), or minimal
load regulation (but some transient overshoot), the
resistance should be kept below 100m. The DC
current rating of the inductor should be at least equal to
the maximum load current plus half the ripple current to
prevent core saturation. Table 1 lists some typical
surface mount inductors that meet target applications for
the APS2415.
Table 1. Typical Surface Mount Inductors
Part Number L
MaxDC DCR
(μH) Current (m)
(A)
Sumida
2.2 3.0
28.7
CDRH5D16 3.3 2.6
35.6
Sumida
CDRH8D28
4.7
3.4
19
Coiltronics 2.0 3.3
23
SD53
3.3 2.6
29
4.7 2.1
39
Size
LxWxH
(mm)
5.8x5.8
x1.8
8.3x8.3
x3.0
5.2x5.2
x3.0
Input Capacitor Selection
The input capacitor reduces the surge current drawn
from the input and switching noise from the device.
The input capacitor impedance at the switching
frequency shall be less than input source impedance to
prevent high frequency switching current passing to the
input. A low ESR input capacitor sized for maximum
RMS current must be used. Ceramic capacitors with
X5R or X7R dielectrics are highly recommended
because of their low ESR and small temperature
coefficients. A 22µF ceramic capacitor for most
applications is sufficient.
Output Capacitor Selection
The output capacitor is required to keep the output
voltage ripple small and to ensure regulation loop
stability. The output capacitor must have low
impedance at the switching frequency. Ceramic
capacitors with X5R or X7R dielectrics are
recommended due to their low ESR and high ripple
current. The output ripple VOUT is determined by:
ΔVOUT
VOUT × (VIN VOUT
VIN × f OSC × L
)
×
⎜⎜⎝⎛
ESR
+
8
×
1
f osc
×
C3
⎟⎟⎠⎞
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APS2415
Package Information
Chipown
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Important Notice
Chipown Microelectronics Co. Ltd. reserves the right to make changes without further notice to any products or
specifications herein. Chipown Microelectronics Co. Ltd. does not assume any responsibility for use of any its
products for any particular purpose, nor does Chipown Microelectronics Co. Ltd assume any liability arising out of the
application or use of any its products or circuits. Chipown Microelectronics Co. Ltd does not convey any license under
its patent rights or other rights nor the rights of others.
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