Skyworks AAT2114A 2.5a low-noise, fast transient 3mhz step-down regulator Datasheet

DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
General Description
Features
The AAT2114A SwitchReg™ step-down converter delivers up to 2.5A to support the adjustable 1.0V to VIN
output from the 2.7V to 5.5V input source. The 3MHz
switching frequency allows a high-bandwidth design that
minimizes the external LC component requirements.
• 2.5A Maximum Output Current
• 3MHz Switching Frequency
▪ Stable With 20μF Output Capacitor
• 2.7V to 5.5V Input Voltage Range
• Adjustable 1.0V to VIN Output Voltage
• Up to 95% Efficiency
• Excellent Current-Mode Transient Response
• Low-Noise Light-Load Architecture
• 70μA No Load Quiescent Current
• No External Compensation Required
• Internal Soft Start
• Over-Temperature and Current-Limit Protection
• <1μA Shutdown Current
• -40°C to +85°C Temperature Range
• 16-Pin, 3mm x 3mm QFN Package
The AAT2114A high-frequency converter consumes only
70μA no-load quiescent current. The internally compensated, high-frequency, current-mode control scheme provides excellent transient response, minimal output ripple,
and reduced spectral noise. Additionally, the AAT2114A
provides tight output accuracy across the entire load and
input voltage operating ranges.
The regulator maintains high efficiency by integrating
the high-side and low-side MOSFETs and designing the
gate drivers to minimize dead-time switching losses. The
regulator also reduces the switching frequency under
light load conditions, minimizing power loss over the
entire load range.
Applications
•
•
•
•
For system fault protection, the AAT2114A includes overtemperature and short-circuit current-limit protection to
safeguard the AAT2114A and system components from
overload conditions.
Cellular Phones
Digital Cameras
MP3/Portable Media Players
Wireless Cards
The compact 3mm x 3mm QFN package footprint, minimal LC requirements, and high efficiency make the
AAT2114A an ideal choice for low-power portable applications operating from a Li-ion/polymer battery.
Typical Application
Load Transient Response
Output Voltage (top) (V)
1.4
1.3
1.2
190mV
1.1
3
2
1
0
Output Current (bottom) (A)
(250mA to 2.5A; VIN = 3.6V; VOUT = 1.2V;
COUT = 2x10µF; CFF = 100pF)
VIN
2.7V-5.5V
9
10,11,12
CIN
10μF
6V
0603
VCC
VP
LX
13,14,15
16
N/C
RFBH
59kΩ
AAT2114A
1, 2, 3
PGND
FB
4
6
ON
N/C
7
8
RFBL
59kΩ
CFF
100pF
COUT
2x10μF
6V
0603
5
EN
OFF
VOUT
1.2V, 2.5A
L1 0.47μH
N/C
SGND
GND
EP
Time (50µs/div)
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1
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Pin Descriptions
Pin #
Name
1, 2, 3
PGND
4
FB
5
SGND
6, 8, 16
N/C
7
EN
9
VCC
10, 11, 12
VP
13, 14, 15
LX
EP
GND
Function
Power Ground. PGND is internally connected to the source of the low-side N-channel MOSFET. Connect to
the input capacitor and output capacitor return.
Feedback Input. FB senses the output voltage for regulation control. Connect a resistive divider network from the output to FB to SGND to set the output voltage accordingly. The adjustable FB regulation
threshold is 0.6V.
Signal/Analog Ground. SGND is internally connected to the analog ground of the control circuitry. Connect the return of the feedback components to this ground.
Not Internally Connected. This pin is not internally connected and may be either left open or shorted to
an adjacent pin.
Enable Input. A logic high enables the AAT2114A regulator. A logic low forces the AAT2114A into shutdown mode, placing the output into a high-impedance state and reducing the quiescent current to less
than 1μA. Do NOT leave EN floating.
Bias Input Supply. VCC supplies power to the analog and logic signal control circuitry of the AAT2114A.
Input Power Supply. Connect VP to the input power source. Bypass VP to PGND with a 10μF or greater
ceramic capacitor. VP internally connects to the source of the high-side P-channel MOSFET and MOSFET
drivers as shown in the Functional Block Diagram.
Inductor Switching Node. LX is internally connected to the source of the high-side P-Channel MOSFET
and the drain of the low-side N-channel MOSFET. Externally connected to the power inductor as shown in
the Typical Application Circuit.
Thermal/Substrate Ground. GND is internally connected to the substrate of the controller and serves as
the lowest thermal impedance path. Connect directly to the system ground plane to keep the thermal
impedance low.
Pin Configuration
QFN33-16
(Top View)
LX
LX
LX
N/C
13
14
15
16
PGND
PGND
PGND
FB
1
12
2
11
EP
3
10
4
9
VP
VP
VP
VCC
8
7
6
5
N/C
EN
N/C
SGND
2
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DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Absolute Maximum Ratings1
Symbol
VP
VCC
VLX
VEN
VFB
VGND
TJ
TLEAD
TA
Description
VP to PGND
VCC to SGND
LX to PGND
EN to SGND
FB to SGND
SGND to GND, PGND to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec.)
Ambient Temperature Range
Value
Units
-0.3 to +6
-0.3 to +6
-0.3 to (VP + 0.3)
-0.3 to (VCC + 0.3)
-0.3 to (VCC + 0.3)
-0.3 to +0.3
-40 to +150
300
-40 to +85
V
V
V
V
V
V
C
C
C
Value
Units
43
2.3
C/W
W
Thermal Characteristics
Symbol
Description
QFN33-16 Thermal Impedance2
θJA
Maximum Junction-to-Ambient Thermal Resistance
PD
Maximum Power Dissipation3
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on a FR4 demo board in still air. The exposed pad must be mounted to the PCB.
3. Derate 23mW/°C above 25°C.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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3
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Electrical Characteristics1
Typical Application Circuit: CIN = 10μF, COUT = 2x 10μF, L = 0.47μH. VP = 3.6V, VCC = EN = VP, SGND = PGND = GND.
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
Symbol
Description
Conditions
VIN
VOUT
Input Voltage Range
Output Voltage Range
VP, VCC
VUVLO
Input Under-Voltage Lockout
IQ
ISHDN
VFB
IFB
ΔVOUT/IOUT
ΔVOUT/VIN
ILIMPK
RDS(ON)HI
RDS(ON)LO
fOSC
tSS
TSHDN
VEN
IEN
No Load Supply Current
Shutdown Current
FB Regulation Threshold
FB Leakage Current
Load Regulation2
Line Regulation
High-Side P-Channel MOSFET Current Limit
High-Side P-Channel MOSFET On-Resistance
Low-Side N-Channel MOSFET On-Resistance
Internal Oscillator Frequency
Soft-Start Period
Over-Temperature Shutdown Threshold
EN Input Logic Threshold
EN Input Current
VCC Rising
Hysteresis
No Load Current; Not Switching
EN = GND, VP = 5.5V, LX = GND
No Load, TA = +25°C, VIN = 5V
VFB = 1.0V
0.25 to 2.5A Load
VIN = 2.7V to 5.5V
Min
Typ
2.7
1.0
0.1
70
591
600
5
1
0.5
Max
Units
5.5
VIN
2.7
V
V
V
V
μA
μA
mV
nA
%
%/V
A
mΩ
mΩ
MHz
μs
°C
V
μA
140
1
609
200
2
3
VIN = 3.3V
2.2
Hysteresis = 15°C
VIN = VEN = 0V or 5.5V
120
100
3.0
60
140
0.4
-1.0
3.8
1.4
+1.0
1. The AAT2114A is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
2. Guaranteed by design.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Typical Characteristics
Efficiency vs. Load
Load Regulation
(VOUT = 3.3V; L = 1.5µH)
(VOUT = 3.3V; L = 1.5µH)
100
Efficiency (%)
80
70
60
50
40
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
30
20
0.1
1
10
100
1000
Output Voltage Error (%)
3.0
90
2.0
1.0
0.0
-1.0
-3.0
0.1
10000
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
-2.0
1
Output Current (mA)
Load Regulation
(VOUT = 2.5V; L = 1µH)
(VOUT = 2.5V; L = 1µH)
70
60
50
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
40
1
10
100
1000
Output Voltage Error (%)
Efficiency (%)
80
30
10000
2.0
1.0
0.0
-1.0
-3.0
0.1
10000
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
-2.0
1
Output Current (mA)
10
100
1000
Efficiency vs. Load
Load Regulation
(VOUT = 1.8V; L = 0.86µH)
(VOUT = 1.8V; L = 0.86µH)
80
70
60
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
40
30
1
10
100
Output Current (mA)
1000
10000
Output Voltage Error (%)
3.0
90
50
10000
Output Current (mA)
100
Efficiency (%)
1000
3.0
90
20
0.1
100
Efficiency vs. Load
100
20
0.1
10
Output Current (mA)
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
2.0
1.0
0.0
-1.0
-2.0
-3.0
0.1
1
10
100
1000
10000
Output Current (mA)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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5
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Typical Characteristics
Efficiency vs. Load
Load Regulation
(VOUT = 1.2V; L = 0.47µH)
(VOUT = 1.2V; L = 0.47µH)
100
Output Voltage Error (%)
3.0
Efficiency (%)
90
80
70
60
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
50
40
30
20
0.1
1
10
100
1000
10000
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
2.0
1.0
0.0
-1.0
-2.0
0.1
1
Output Current (mA)
Line Regulation
(VOUT = 1.2V; L = 0.47µH)
1.0
0.5
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
0.0
-0.5
-1.0
-1.5
-2.0
3.0
3.5
4.0
4.5
5.0
Output Voltage Error (%)
2.0
2.5
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
1.5
1.0
0.0
-1.0
-1.5
-2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Output Voltage Error vs. Temperature
(VIN = 4.2V; VOUT = 3.3V)
(VIN = 3.6V; VOUT = 2.5V)
3.0
3.0
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
Output Voltage Error (%)
Output Voltage Error (%)
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
-0.5
5.5
Output Voltage Error vs. Temperature
1.0
0.0
-1.0
-2.0
-25
0
25
50
Temperature (°C)
6
10000
0.5
Input Voltage (V)
-3.0
-50
1000
Line Regulation
1.5
2.0
100
(VOUT = 1.8V; L = 0.86µH)
2.0
Output Voltage Error (%)
10
Output Current (mA)
75
100
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
2.0
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
1.0
0.0
-1.0
-2.0
-3.0
-50
-25
0
25
50
Temperature (°C)
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75
100
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Typical Characteristics
Output Voltage Error vs. Temperature
Output Voltage Error vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
(VIN = 3.6V; VOUT = 1.2V)
3.0
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
2.0
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
Output Voltage Error (%)
Output Voltage Error (%)
3.0
1.0
0.0
-1.0
-2.0
-3.0
-50
-25
0
25
50
75
100
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
2.0
1.0
0.0
-1.0
-2.0
-3.0
-50
Temperature (°C)
-25
0
25
50
75
100
Temperature (°C)
Load Transient Response
Load Transient Response
(250mA to 2.5A; VIN = 5.0V; VOUT = 3.3V;
COUT = 2x10µF; C5 = 100pF)
(250mA to 2.5A; VIN = 3.6V; VOUT = 2.5V;
COUT = 2x10µF; C5 = 100pF)
2.9
3.5
2.7
3.1
3
2
2.5
2.3
3
2
1
1
Output Current
(bottom) (A)
3.3
Output Voltage
(top) (V)
3.7
Output Current
(bottom) (A)
Output Voltage
(top) (V)
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
0
0
Time (50µs/div)
Load Transient Response
Load Transient Response
(250mA to 2.5A; VIN = 3.6V; VOUT = 1.8V;
COUT = 2x10µF; C5 = 100pF)
(250mA to 2.5A; VIN = 3.6V; VOUT = 1.2V;
COUT = 2x10µF; C5 = 100pF)
1.4
1.9
1.3
1.7
3
2
1
1.2
1.1
3
2
1
0
0
Time (50µs/div)
Output Current
(bottom) (A)
1.8
Output Voltage
(top) (V)
2.0
Output Current
(bottom) (A)
Output Voltage
(top) (V)
Time (50µs/div)
Time (50µs/div)
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DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Line Transient Response
Line Transient Response
(VIN = 3.6V to 4.2V; VOUT = 2.5V; IOUT = 2.5A;
COUT = 2x10µF; C5 = 100pF)
(VIN = 3.6V to 4.2V; VOUT = 1.8V; IOUT = 2.5A;
COUT = 2x10µF; C5 = 100pF)
4.8
4.2
4.2
3.0
2.52
2.50
3.6
3.0
1.82
1.80
2.48
1.78
2.46
1.76
Time (20µs/div)
Time (20µs/div)
Output Ripple
Output Ripple
(VIN = 3.6V; VOUT = 1.2V; IOUT = 10mA)
(VIN = 3.6V; VOUT = 1.2V; IOUT = 2.5A)
1.24
1.24
0.6
0.4
0.2
1.20
1.18
3.0
2.5
2.0
0.0
1.5
Time (10µs/div)
Time (200ns/div)
Enable Soft Start
4
3
2
1
3
0
2
1
Inductor Current
(bottom) (A)
Enable Voltage (top) (V)
Output Voltage (middle) (V)
(VIN = 3.6V; VOUT = 1.2V; IOUT = 2.5A)
0
Time (20µs/div)
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Inductor Current
(bottom) (A)
1.18
Output Voltage
(top) (V)
1.22
1.20
Inductor Current
(bottom) (A)
Output Voltage
(top) (V)
1.22
8
Output Voltage
(bottom) (V)
3.6
Input Voltage
(top) (V)
4.8
Output Voltage
(bottom) (V)
Input Voltage
(top) (V)
Typical Characteristics
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Typical Characteristics
Switching Frequency vs. Input Voltage
Switching Frequency vs. Temperature
(VOUT = 1.2V; IOUT = 2.5A)
(VIN = 3.6V; IOUT = 2.5A; VOUT = 1.2A)
Switching Frequency (MHz)
Frequency Variation (%)
10
8
6
4
2
0
-2
-4
-6
-8
-10
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
3.30
3.20
3.10
3.00
2.90
2.80
2.70
-40
-20
0
Input Voltage (V)
20
40
60
80
100
Temperature (°C)
Input Current vs. Input Voltage
Enable Threshold vs. Input Voltage
100
1.2
90
1.1
VIH and VIL (V)
Input Current (µA)
(VEN = VIN; VOUT = 1.2V; Closed Loop Switching)
80
70
60
50
85°C
25°C
-40°C
40
30
2.5
3
3.5
4
4.5
Input Voltage (V)
5
5.5
1.0
0.9
0.8
EN Rising
EN Falling
0.7
0.6
6
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
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9
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Functional Block Diagram
VCC
VP
Slope
Compensation
FB
SGND
VP
0.6V
REF
OSC
PGND
Temperature
Sensing
EN
Functional Description
The AAT2114A is a high performance 2.5A monolithic
step-down converter operating at a 3MHz switching frequency. It minimizes external component size, optimizes
efficiency over the complete load range, and produces
reduced ripple and spectral noise. Apart from the small
bypass input capacitor, only a small L-C filter is required
at the output. Typically, a 0.47μH inductor and a 22μF
ceramic capacitor are recommended for a 1.2V output
(see table of recommended values).
Light load operation maintains high efficiency, low ripple
and low spectral noise even at lower currents (typically
<150mA).
The current limit of 4A (typical) protects the IC and system components from short-circuit damage. Typical no
load quiescent current is 70μA.
Thermal protection completely disables switching when
the maximum junction temperature is detected. The
junction over-temperature threshold is 140°C with 15°C
of hysteresis. Once an over-temperature or over-current
fault condition is removed, the output voltage automatically recovers.
Peak current mode control and optimized internal compensation provide high loop bandwidth and excellent
response to input voltage and fast load transient events.
Soft start eliminates output voltage overshoot when the
10
Control
Logic
LX
enable or the input voltage is applied. Under-voltage
lockout prevents spurious start-up events.
Control Loop
The AAT2114A is a peak current mode step-down converter. The current through the P-channel MOSFET (high
side) is sensed for current loop control, as well as short
circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage-programmed current source in parallel with the output capacitor.
The output of the voltage error amplifier programs the
current mode loop for the necessary peak switch current
to force a constant output voltage for all load and line
conditions. Internal loop compensation determines the
transconductance voltage error amplifier output. The
0.6V reference voltage is internally set to program the
converter output voltage greater than or equal to 1.0V.
Soft Start/Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT2114A into a low-power,
non-switching state. The total input current during shutdown is less than 1μA.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Current Limit and
Over-Temperature Protection
appreciable saturation under normal load conditions.
For overload conditions, the peak input current is limited. The on-time is terminated after a current limit has
been sensed.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Under-Voltage Lockout
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor.
Input Capacitor
Select a 10μF to 22μF X7R or X5R ceramic capacitor for
the input. To estimate the required input capacitor size,
determine the acceptable input ripple level (VPP) and solve
for CIN. The calculated value varies with input voltage and
is a maximum when VIN is double the output voltage.
Internal bias of all circuits is controlled via the VCC
input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation.
CIN(MIN) =
Component Selection
VPP
- ESR · FSW
IO
D=
Inductor Selection
The step-down converter uses peak current mode control with slope compensation to maintain stability for
duty cycles greater than 50%. The output inductor value
must be selected so the inductor current down slope
meets the internal slope compensation requirements.
The inductor value can be calculated by:
L1 =
D · (1 - D)
0.47 · VOUT
1.2
For low cost application and a sufficiently small footprint,
the TDK VLS252012T-R47N2R1 shielded chip inductor,
which has 47mΩ DCR, is selected for 1.2V output (see
Table 1).
VO
VIN
The peak ripple voltage occurs when VIN = 2x VO (50%
duty cycle), resulting in a minimum output capacitance
recommendation:
CIN(MIN) =
1
VPP
- ESR · 4 · FS
IO
Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value.
For example, the capacitance of a 10μF, 6.3V, X5R
ceramic capacitor with 5.0V DC applied is actually about
6μF. The maximum input capacitor RMS current is:
IRMS = IO ·
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and the
peak current rating, which is determined by the saturation characteristics. The inductor should not show any
IRMS = IO ·
D · (1 - D)
VO
V
· 1- O
VIN
VIN
VOUT (V)
Inductor Selection
1.2
1.8
2.5
3.3
TDK, VLS252012T-R47N2R1, 0.47μH, ISAT = 3.7A, DCR = 47mΩ
Sumida, CDRH38D16R/HP, 0.9μH, ISAT = 2.66A, DCR = 20mΩ
TDK, VLS252012T-1R0N1R7, 1.0μH, ISAT = 2.7A, DCR = 88mΩ
TDK, VLF5014AT-1R5M1R7, 1.5μH, ISAT = 2.9, DCR = 51mΩ
Table 1: Inductor Selection.
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11
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
The input capacitor RMS ripple current varies with the
input and output voltage and will always be less than or
equal to half of the total DC load current.
IRMS(MAX) =
IO
2
occurs when VIN = 2 · VO.
The calculated value varies with the input voltage and is
at a maximum when VIN is twice the output voltage VOUT.
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT2114A.
Low ESR/ESL X7R and X5R ceramic capacitors are ideal
for this function. To minimize stray inductance, the
capacitor should be placed as closely as possible to the
IC. This keeps the high frequency content of the input
current localized, minimizing EMI and input voltage ripple.
The proper placement of the input capacitor can be seen
in the evaluation board layout shown in Figure 2.
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain
measurements can also result.
Since the inductance of a short PCB trace feeding the
input voltage is significantly lower than the power leads
from the bench power supply, most applications do not
exhibit this problem.
In applications where the input power source lead inductance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the
low ESR/ESL bypass ceramic capacitor. This dampens
the high Q network and stabilizes the system.
Output Capacitor
The output capacitor limits the output ripple and maintains the output voltage during large load transitions. A
22μF X5R or X7R ceramic capacitor typically provides
sufficient bulk capacitance to stabilize the output during
large load transitions and has the ESR and ESL characteristics necessary for low output ripple.
12
The output voltage droop due to a load transient is
dominated by the capacitance of the ceramic output
capacitor. During a step increase in load current, the
ceramic output capacitor alone supplies the load current
until the loop responds. Within two or three switching
cycles, the loop responds and the inductor current
increases to match the load current demand. The relationship of the output voltage droop during the three
switching cycles to the output capacitance can be estimated by:
COUT =
3 · ΔIO
VDROOP · FSW
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equation establishes a limit on the minimum value for the
output capacitor with respect to load transients.
The internal voltage loop compensation also limits the
minimum output capacitor value to 20μF. This is due to
its effect on the loop crossover frequency (bandwidth),
phase margin, and gain margin. Increased output capacitance will reduce the crossover frequency with greater
phase margin.
Adjustable Feedback Network
The output voltage on the AAT2114A is programmed
with external resistors R3 and R4. To limit the bias current required for the external feedback resistor string
while maintaining good noise immunity. Although a
larger value will further reduce quiescent current, it will
also increase the impedance of the feedback node, making it more sensitive to external noise and interference.
Therefore, the recommended value range for R4 is 59kΩ
for good noise immunity or 221kΩ for reduced no load
input current.
The external resistor R3, combined with an external
100pF feed forward capacitor (C5 in Figure 1), delivers
enhanced transient response for extreme pulsed load
applications and reduces ripple in light load conditions.
The external resistors set the output voltage according
to the following equation:
VO = 0.6V · 1 +
R3
R4
or solving for R3:
R3 =
VO
- 1 · R4
0.6V
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
The typical circuit shown in the AAT2114A evaluation
schematic is intended to be general purpose and suitable
for most applications. In applications where transient
load steps are more severe and the restriction on output
voltage deviation is more stringent, some simple adjustments can be made. The schematic in Figure 1 shows
the configuration for improved transient response in an
application where the output is stepped down to 1.2V.
The adjustments consist of increasing the value of the
feed forward capacitor C5 to 100pF.
VOUT (V)
R4 = 59.0kΩ
R3 (kΩ)
R4 = 221kΩ
R3 (kΩ)
1.0
1.2
1.5
1.8
2.5
3.3
39.2
59
88.7
118
187
267
147
221
332
442
698
1M
Table 2: Feedback Resistors for
Various Output Voltages.
Thermal Calculations
There are three types of losses associated with the
AAT2114A step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction
losses are associated with the RDS(ON) characteristics of the
power output switching devices. Switching losses are
dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction
mode (CCM), a simplified form of the losses is given by:
PLOSS(RES) = IO2 · RDS(ON)H ·
VO
VIN
+ RDS(ON)L ·
VIN - VO
VIN
+ (tSW · FSW · IOUT + IQ) · VIN
IQ is the step-down converter quiescent current. The
term tSW is the time to charge up the gate capacitor of
the high-side P-channel MOSFET, and used to estimate
the full load step-down converter switching losses.
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be investigated over the complete input voltage range.
Given the total losses, the maximum junction temperature can be derived from the θJA for the QFN33-16 package, which is 43°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
Layout Considerations
The suggested PCB layout for the AAT2114A is shown in
Figures 2 and 3. The following guidelines should be used
to help ensure a proper layout.
1.
The input capacitor (C1) should connect as close as
possible to VP and PGND.
2. C2, C3 and L1 should be connected as close as possible. The connection of L1 to the LX pin should be as
short as possible.
3. The feedback trace or FB pin should be separate
from any power trace and connect as close as possible to the load point. Sensing along a high-current
load trace will degrade DC load regulation.
4. The resistance of the trace from the load return to
PGND should be kept to a minimum. This will help to
minimize any error in DC regulation due to differences in the potential of the internal signal ground
and the power ground.
5. Connect unused signal pins to ground to avoid
unwanted noise coupling.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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13
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
U1
VIN
10
11
12
C1
10μF
C6
Open
R1
10Ω
9
VP
LX
VP
LX
VP
LX
AAT2114A
N/C
VCC
FB
C4
0.1μF
N/C
SGND
EN
7
EN
PGND
1
U1
C1, C2, C3
C4
C5
L1
R1
R3, R4
2
13
VOUT
L1 0.47μH
14
R3
59kΩ
15
C5
100pF
1.2V/2.5A
16
C2
10μF
4
C3
10μF
C7
Open
8
R4
59kΩ
5
N/C
3
6
QFN 33 -16
AAT2114AIVN, Skyworks, 3MHz Fast Transient, 2.5A Step-Down Converter, QFN33-16, 3x3mm
GRM188R60J106ME47D, Murata, Cap, MLC, 10μF/6.3V, 0603
0.1μF/6.3V, 0402
UMK105CG101JV-F10nF, Taiyo Yuden, 100pF/50V, 0402
252012T-R47N2R1, TDK, 0.47μH, ISAT = 3.7A, DCR = 0.047Ω, 2.5x2x1.2mm, shielded chip inductor
Carbon film resistor, 10Ω, 1%, 0201
Carbon film resistor, 59kΩ, 1%, 0402
Figure 1: AAT2114AIVN Evaluation Board Schematic and Bill of Materials.
Figure 2: AAT2114AIVN Evaluation Board
Top Side Layout.
14
Figure 3: AAT2114AIVN Evaluation Board
Bottom Side Layout.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202004C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Ordering Information
Package
Output
Marking1
Part Number (Tape and Reel)2
QFN33-16
Adjustable (VFB = 0.6V)
M7XYY
AAT2114AIVN-0.6-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information
QFN33-163
Pin 1 Dot By Marking
0.230 ± 0.050
Pin 1 Identification
0.500 ± 0.050
1.250 ± 0.050
5
C0.3
13
9
1.250 ± 0.050
Top View
0.025 ± 0.025
Bottom View
0.214 ± 0.036
0.900 ± 0.100
3.000 ± 0.050
0.400 ± 0.100
3.000 ± 0.050
1
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN, and STDFN, has exposed copper (unplated) at the end of the lead terminals due to manufacturing process.
A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202004C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
15
DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Copyright © 2012, 2013 Skyworks Solutions, Inc. All Rights Reserved.
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202004C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013