1
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
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General Description
The AAT2114A SwitchReg™ step-down converter deliv-
ers 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.
The AAT2114A high-frequency converter consumes only
70A no-load quiescent current. The internally compen-
sated, high-frequency, current-mode control scheme pro-
vides 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.
For system fault protection, the AAT2114A includes over-
temperature and short-circuit current-limit protection to
safeguard the AAT2114A and system components from
overload conditions.
The compact 3mm x 3mm QFN package footprint, mini-
mal LC requirements, and high efficiency make the
AAT2114A an ideal choice for low-power portable applica-
tions operating from a Li-ion/polymer battery.
Features
• 2.5A Maximum Output Current
• 3MHz Switching Frequency
Stable With 20F 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
• 70A No Load Quiescent Current
• No External Compensation Required
• Internal Soft Start
• Over-Temperature and Current-Limit Protection
• <1A Shutdown Current
• -40°C to +85°C Temperature Range
• 16-Pin, 3mm x 3mm QFN Package
Applications
• Cellular Phones
• Digital Cameras
• MP3/Portable Media Players
• Wireless Cards
Typical Application
Load Transient Response
(250mA to 2.5A; VIN = 3.6V; VOUT = 1.2V;
COUT = 2x10µF; CFF = 100pF)
Time (50µs/div)
Output Voltage (top) (V)
Output Current (bottom) (A)
1.1
1.2
1.3
1.4
0
1
2
3
190mV
5
10,11,12
13,14,15
7
9
4
1, 2, 3
ON
OFF
CIN
10µF
6V
0603 RFBL
59kΩ
CFF
100pF
COUT
2x10µF
6V
0603
VOUT
1.2V, 2.5A
RFBH
59kΩ
VIN
2.7V-5.5V
L1 0.47µH
EP
6
8
16
VP
EN
VCC
SGND
LX
FB
PGND
AAT2114A
GND
N/C
N/C
N/C
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2
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Pin Descriptions
Pin # Name Function
1, 2, 3 PGND 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.
4FB
Feedback Input. FB senses the output voltage for regulation control. Connect a resistive divider net-
work from the output to FB to SGND to set the output voltage accordingly. The adjustable FB regulation
threshold is 0.6V.
5 SGND Signal/Analog Ground. SGND is internally connected to the analog ground of the control circuitry. Con-
nect the return of the feedback components to this ground.
6, 8, 16 N/C Not Internally Connected. This pin is not internally connected and may be either left open or shorted to
an adjacent pin.
7EN
Enable Input. A logic high enables the AAT2114A regulator. A logic low forces the AAT2114A into shut-
down mode, placing the output into a high-impedance state and reducing the quiescent current to less
than 1A. Do NOT leave EN fl oating.
9 VCC Bias Input Supply. VCC supplies power to the analog and logic signal control circuitry of the AAT2114A.
10, 11, 12 VP
Input Power Supply. Connect VP to the input power source. Bypass VP to PGND with a 10F 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.
13, 14, 15 LX
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.
EP GND
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)
VP
VP
VP
N/C
PGND
PGND
PGND
1
2
3
4
N/C
SGND
EN
16
15
14
13
5
6
7
8
12
11
EP
10
9
N/C
VCC
LX
LX
LX
FB
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
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.
Absolute Maximum Ratings1
Symbol Description Value Units
VPVP to PGND -0.3 to +6 V
VCC VCC to SGND -0.3 to +6 V
VLX LX to PGND -0.3 to (VP + 0.3) V
VEN EN to SGND -0.3 to (VCC + 0.3) V
VFB FB to SGND -0.3 to (VCC + 0.3) V
VGND SGND to GND, PGND to GND -0.3 to +0.3 V
TJOperating Junction Temperature Range -40 to +150 C
TLEAD Maximum Soldering Temperature (at leads, 10 sec.) 300 C
TAAmbient Temperature Range -40 to +85 C
Thermal Characteristics
Symbol Description Value Units
QFN33-16 Thermal Impedance2
JA Maximum Junction-to-Ambient Thermal Resistance 43 C/W
PDMaximum Power Dissipation32.3 W
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4
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
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 cor-
relation with statistical process controls.
2. Guaranteed by design.
Electrical Characteristics1
Typical Application Circuit: CIN = 10F, C OUT = 2x 10F, L = 0.47H. 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 Min Typ Max Units
VIN Input Voltage Range VP, VCC 2.7 5.5 V
VOUT Output Voltage Range 1.0 VIN V
VUVLO Input Under-Voltage Lockout VCC Rising 2.7 V
Hysteresis 0.1 V
IQNo Load Supply Current No Load Current; Not Switching 70 140 A
ISHDN Shutdown Current EN = GND, VP = 5.5V, LX = GND 1 A
VFB FB Regulation Threshold No Load, TA = +25°C, VIN = 5V 591 600 609 mV
IFB FB Leakage Current VFB = 1.0V 5 200 nA
VOUT/IOUT Load Regulation20.25 to 2.5A Load 1 2 %
VOUT/VIN Line Regulation VIN = 2.7V to 5.5V 0.5 %/V
ILIMPK High-Side P-Channel MOSFET Current Limit 3 A
RDS(ON)HI High-Side P-Channel MOSFET On-Resistance 120 m
RDS(ON)LO Low-Side N-Channel MOSFET On-Resistance 100 m
fOSC Internal Oscillator Frequency VIN = 3.3V 2.2 3.0 3.8 MHz
tSS Soft-Start Period 60 s
TSHDN Over-Temperature Shutdown Threshold Hysteresis = 15°C 140 °C
VEN EN Input Logic Threshold 0.4 1.4 V
IEN EN Input Current VIN = VEN = 0V or 5.5V -1.0 +1.0 A
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Typical Characteristics
Efficiency vs. Load
(V
OUT
= 3.3V; L = 1.5µH)
Output Current (mA)
Efficiency (%)
0.1 1 10 100 1000 10000
20
30
40
50
60
70
80
90
100
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
Load Regulation
(V
OUT
= 3.3V; L = 1.5µH)
Output Current (mA)
Output Voltage Error (%)
0.1 1 10 100 1000 10000
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
Efficiency vs. Load
(V
OUT
= 2.5V; L = 1µH)
Output Current (mA)
Efficiency (%)
0.1 1 10 100 1000 10000
20
30
40
50
60
70
80
90
100
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
Load Regulation
(V
OUT
= 2.5V; L = 1µH)
Output Current (mA)
Output Voltage Error (%)
0.1 1 10 100 1000 10000
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
Efficiency vs. Load
(V
OUT
= 1.8V; L = 0.86µH)
Output Current (mA)
Efficiency (%)
0.1 1 10 100 1000 10000
20
30
40
50
60
70
80
90
100
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
Load Regulation
(V
OUT
= 1.8V; L = 0.86µH)
Output Current (mA)
Output Voltage Error (%)
0.1 1 10 100 1000 10000
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0 VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
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6
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Typical Characteristics
Efficiency vs. Load
(V
OUT
= 1.2V; L = 0.47µH)
Output Current (mA)
Efficiency (%)
0.1 1 10 100 1000 10000
20
30
40
50
60
70
80
90
100
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
Load Regulation
(V
OUT
= 1.2V; L = 0.47µH)
Output Current (mA)
Output Voltage Error (%)
0.1 1 10 100 1000 10000
-2.0
-1.0
0.0
1.0
2.0
3.0
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
VIN = 5.0V
VIN = 5.5V
Line Regulation
(VOUT = 1.8V; L = 0.86µH)
Input Voltage (V)
Output Voltage Error (%)
2.5 3.0 3.5 4.0 4.5 5.0 5.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
Line Regulation
(VOUT = 1.2V; L = 0.47µH)
Input Voltage (V)
Output Voltage Error (%)
2.5 3.0 3.5 4.0 4.5 5.0 5.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0 IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
Output Voltage Error vs. Temperature
(V
IN
= 4.2V; V
OUT
= 3.3V)
Temperature (°C)
Output Voltage Error (%)
-50 -25 0 50 7525 100
-3.0
-2.0
-1.0
0.0
1.0
2.0
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 vs. Temperature
(V
IN
= 3.6V; V
OUT
= 2.5V)
Temperature (°C)
Output Voltage Error (%)
-50 -25 0 50 7525 100
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Typical Characteristics
Output Voltage Error vs. Temperature
(V
IN
= 3.6V; V
OUT
= 1.8V)
Temperature (°C)
Output Voltage Error (%)
-50 -25 0 50 7525 100
-3.0
-2.0
-1.0
0.0
1.0
2.0
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 vs. Temperature
(V
IN
= 3.6V; V
OUT
= 1.2V)
Temperature (°C)
Output Voltage Error (%)
-50 -25 0 50 7525 100
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
IOUT = 0.10mA
IOUT = 1mA
IOUT = 10mA
IOUT = 0.1A
IOUT = 0.5A
IOUT = 1.25A
IOUT = 2A
IOUT = 2.5A
Load Transient Response
(250mA to 2.5A; VIN = 5.0V; VOUT = 3.3V;
COUT = 2x10µF; C5 = 100pF)
Time (50µs/div)
Output Voltage
(top) (V)
Output Current
(bottom) (A)
3.1
3.3
3.5
3.7
0
1
2
3
Load Transient Response
(250mA to 2.5A; VIN = 3.6V; VOUT = 2.5V;
COUT = 2x10µF; C5 = 100pF)
Time (50µs/div)
Output Voltage
(top) (V)
Output Current
(bottom) (A)
2.3
2.5
2.7
2.9
0
1
2
3
Load Transient Response
(250mA to 2.5A; VIN = 3.6V; VOUT = 1.8V;
COUT = 2x10µF; C5 = 100pF)
Time (50µs/div)
Output Voltage
(top) (V)
Output Current
(bottom) (A)
1.7
1.8
1.9
2.0
0
1
2
3
Load Transient Response
(250mA to 2.5A; VIN = 3.6V; VOUT = 1.2V;
COUT = 2x10µF; C5 = 100pF)
Time (50µs/div)
Output Voltage
(top) (V)
Output Current
(bottom) (A)
1.1
1.2
1.3
1.4
0
1
2
3
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8
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Typical Characteristics
Line Transient Response
(VIN = 3.6V to 4.2V; VOUT = 2.5V; IOUT = 2.5A;
COUT = 2x10µF; C5 = 100pF)
Time (20µs/div)
Input Voltage
(top) (V)
Output Voltage
(bottom) (V)
3.0
3.6
4.2
4.8
2.46
2.48
2.50
2.52
Line Transient Response
(VIN = 3.6V to 4.2V; VOUT = 1.8V; IOUT = 2.5A;
COUT = 2x10µF; C5 = 100pF)
Time (20µs/div)
Input Voltage
(top) (V)
Output Voltage
(bottom) (V)
3.0
3.6
4.2
4.8
1.76
1.78
1.80
1.82
Output Ripple
(VIN = 3.6V; VOUT = 1.2V; IOUT = 10mA)
Time (10µs/div)
Output Voltage
(top) (V)
Inductor Current
(bottom) (A)
1.18
1.20
1.22
1.24
0.0
0.2
0.4
0.6
Output Ripple
(VIN = 3.6V; VOUT = 1.2V; IOUT = 2.5A)
Time (200ns/div)
Output Voltage
(top) (V)
Inductor Current
(bottom) (A)
1.18
1.20
1.22
1.24
1.5
2.0
2.5
3.0
Enable Soft Start
(VIN = 3.6V; VOUT = 1.2V; IOUT = 2.5A)
Time (20µs/div)
Enable Voltage (top) (V)
Output Voltage (middle) (V)
Inductor Current
(bottom) (A)
0
1
2
3
4
0
1
2
3
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Typical Characteristics
Switching Frequency vs. Input Voltage
(VOUT = 1.2V; IOUT = 2.5A)
Input Voltage (V)
Frequency Variation (%)
2.7 3.5 4.3 5.13.1 3.9 4.7 5.5
-10
-8
-6
-4
-2
0
2
4
6
8
10
Switching Frequency vs. Temperature
(VIN = 3.6V; IOUT = 2.5A; VOUT = 1.2A)
Temperature (°C)
Switching Frequency (MHz)
-40 -20 0 20 40 60 80 100
2.70
2.80
2.90
3.00
3.10
3.20
3.30
Input Current vs. Input Voltage
(V
EN
= V
IN
; V
OUT
= 1.2V; Closed Loop Switching)
Input Voltage (V)
Input Current (µA)
2.5 3 3.5 4 4.5 5 65.5
30
40
50
60
70
80
90
100
85°C
25°C
-40°C
Enable Threshold vs. Input Voltage
Input Voltage (V)
VIH and VIL (V)
2.5 3.5 4.5 5.53.0 4.0 5.0 6.0
0.6
0.7
0.8
0.9
1.0
1.1
1.2
EN Rising
EN Falling
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10
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Functional Description
The AAT2114A is a high performance 2.5A monolithic
step-down converter operating at a 3MHz switching fre-
quency. 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 0.47H inductor and a 22F
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 sys-
tem components from short-circuit damage. Typical no
load quiescent current is 70A.
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 automati-
cally recovers.
Peak current mode control and optimized internal com-
pensation provide high loop bandwidth and excellent
response to input voltage and fast load transient events.
Soft start eliminates output voltage overshoot when the
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 con-
verter. 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 compensa-
tion signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak cur-
rent mode loop appears as a voltage-programmed cur-
rent 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 shut-
down is less than 1A.
Functional Block Diagram
PGND
FB LX
0.6V
REF
VP
Control
Logic
VCC
SGND
VP
Slope
Compensation
Temperature
Sensing
OSC
EN
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Current Limit and
Over-Temperature Protection
For overload conditions, the peak input current is limit-
ed. 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 hys-
teresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VCC
input. Under-voltage lockout (UVLO) guarantees suffi-
cient VIN bias and proper operation of all internal cir-
cuitry prior to activation.
Component Selection
Inductor Selection
The step-down converter uses peak current mode con-
trol 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:
0.47 · VOUT
1.2
L1 =
For low cost application and a sufficiently small footprint,
the TDK VLS252012T-R47N2R1 shielded chip inductor,
which has 47m DCR, is selected for 1.2V output (see
Table 1).
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 satura-
tion characteristics. The inductor should not show any
appreciable saturation under normal load conditions.
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 10F to 22F 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.
D · (1 - D)
CIN(MIN) =
- ESR · FSW
VPP
IO
VO
VIN
D =
The peak ripple voltage occurs when VIN = 2x VO (50%
duty cycle), resulting in a minimum output capacitance
recommendation:
1
CIN(MIN) =
- ESR · 4 · FS
VPP
IO
Always examine the ceramic capacitor DC voltage coef-
ficient characteristics when selecting the proper value.
For example, the capacitance of a 10F, 6.3V, X5R
ceramic capacitor with 5.0V DC applied is actually about
6F. The maximum input capacitor RMS current is:
I
RMS
= I
O
·
D · (1 - D)
IRMS = IO · · 1 -
VO
VIN
VO
VIN
VOUT (V) Inductor Selection
1.2 TDK, VLS252012T-R47N2R1, 0.47H, ISAT = 3.7A, DCR = 47m
1.8 Sumida, CDRH38D16R/HP, 0.9H, ISAT = 2.66A, DCR = 20m
2.5 TDK, VLS252012T-1R0N1R7, 1.0H, ISAT = 2.7A, DCR = 88m
3.3 TDK, VLF5014AT-1R5M1R7, 1.5H, ISAT = 2.9, DCR = 51m
Table 1: Inductor Selection.
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
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.
IO
2
IRMS(MAX) =
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 rip-
ple.
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 eval-
uation 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 dur-
ing 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 induc-
tance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or alu-
minum 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 main-
tains the output voltage during large load transitions. A
22F X5R or X7R ceramic capacitor typically provides
sufficient bulk capacitance to stabilize the output during
large load transitions and has the ESR and ESL charac-
teristics necessary for low output ripple.
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 rela-
tionship of the output voltage droop during the three
switching cycles to the output capacitance can be esti-
mated by:
COUT =
3 · ΔIO
VDROOP · FSW
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equa-
tion 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 20F. This is due to
its effect on the loop crossover frequency (bandwidth),
phase margin, and gain margin. Increased output capac-
itance 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 cur-
rent 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, mak-
ing it more sensitive to external noise and interference.
Therefore, the recommended value range for R4 is 59k
for good noise immunity or 221k 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 = - 1 · R4
VO
0.6V
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
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 adjust-
ments 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 39.2 147
1.2 59 221
1.5 88.7 332
1.8 118 442
2.5 187 698
3.3 267 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, con-
duction 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 switch-
ing devices. At full load, assuming continuous conduction
mode (CCM), a simplified form of the losses is given by:
P
LOSS(RES)
= I
O2
· R
DS(ON)H
· + R
DS(ON)L
· + (t
SW
· F
SW
· I
OUT
+ I
Q
) · V
IN
V
O
V
IN
V
IN
- V
O
V
IN
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 inves-
tigated over the complete input voltage range.
Given the total losses, the maximum junction tempera-
ture can be derived from the JA for the QFN33-16 pack-
age, 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 pos-
sible. 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 pos-
sible 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 differ-
ences in the potential of the internal signal ground
and the power ground.
5. Connect unused signal pins to ground to avoid
unwanted noise coupling.
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14
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
C1
10µF
C6
Open
C4
0.1µF
C7
Open
C2
10µF
C5
100pF
R3
59kΩ
R1
10Ω
R4
59kΩ
L1 0.47µH
C3
10µF
EN
VP
10
VP
11
N/C 8
LX 13
2
VCC
9
SGND 5
EN
7
1
VP
12
PGND N/C
6
3
FB 4
LX 14
LX 15
N/C 16
QFN 33 -16
U1
VIN VOUT
AAT2114A
U1 AAT2114AIVN, Skyworks, 3MHz Fast Transient, 2.5A Step-Down Converter, QFN33-16, 3x3mm
C1, C2, C3 GRM188R60J106ME47D, Murata, Cap, MLC, 10µF/6.3V, 0603
C4 0.1µF/6.3V, 0402
C5 UMK105CG101JV-F10nF, Taiyo Yuden, 100pF/50V, 0402
L1 252012T-R47N2R1, TDK, 0.47μH, ISAT = 3.7A, DCR = 0.047Ω, 2.5x2x1.2mm, shielded chip inductor
R1 Carbon film resistor, 10Ω, 1%, 0201
R3, R4 Carbon film resistor, 59kΩ, 1%, 0402
1.2V/2.5A
Figure 1: AAT2114AIVN Evaluation Board Schematic and Bill of Materials.
Figure 2: AAT2114AIVN Evaluation Board Figure 3: AAT2114AIVN Evaluation Board
Top Side Layout. Bottom Side Layout.
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AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
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.
Ordering Information
Package Output Marking1Part 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
3.000
±
0.050
Pin 1 Dot By Marking
1.250
±
0.050
0.400
±
0.100
1.250
±
0.050
3.000
±
0.050
0.500
±
0.050
0.900
±
0.100
Pin 1 Identification
C0.3
0.025
±
0.025
0.214
±
0.036
0.230
±
0.050
Top View Bottom View
Side View
1
13
5
9
All dimensions in millimeters.
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16
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
DATA SHEET
Copyright © 2012, 2013 Skyworks Solutions, Inc. All Rights Reserved.
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