Skyworks AAT2612IDG-1-T1 Step-down dc/dc converter with three high psrr ldo Datasheet

DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
General Description
Features
The AAT2612 is a multiple rail power management IC. It
integrates a 600mA high-frequency switching-converter
and three 300mA linear regulators. The switching power
supply is a highly-integrated monolithic step-down converter operating at 1.5MHz, achieving high efficiency with
small external components. The three linear regulators
are high PSRR low dropout regulators (LDOs) providing
accurate regulation and excellent transient response.
• Current Mode Control DC/DC Converter:
▪ Programmable Output Up to 600mA
▪ 1.5MHz Switching Frequency
▪ Up to 90% Efficiency
▪ Integrated Switching Power FETS
▪ Integrated Compensation Network
▪ Internal Current Limit
•3 Low Dropout Regulators with Separate Enable Pins:
▪ 300mA per Channel
▪ High PSRR
▪ Factory Programmable Output
•Integrated Soft-Start
•Over-Current Protection
•Over-Thermal Protection
•TQFN33-20 Package
The step down converter is programmable with external
feedback resistors, and the three LDOs are fixed voltage
outputs of six combinations for 1.8V, 2.8V, 3.0V and 3.3V.
Integrated over-current or over-temperature protection
circuitry becomes active as appropriate, when either fault
occurs, and the AAT2612 recovers automatically when
the fault is removed.
The AAT2612 is available in a Pb-free, thermally enhanced
20-pin TQFN33 package.
Applications
•
•
•
•
•
Cellular Phones
I/O Power
Memory Power
Processor Core Power
Smart Handheld Devices
Typical Application
2.5V to 5.5V
INL1
OUTL1
2.2μF
2.5V to 5.5V
1μF
INL2
OUTL2
1μF
2.2μF
ENL1
ENL2
ENL3
2.8 V
300mA
2.8V
300mA
1.8V
300mA
OUTL3
1μF
AAT2612
2.2μH
ENBK
2.5V to 5.5V
4.7μF
INBK
LX
1.2V , 600mA
10μF
FB
AGND PGND
R1
59k
R2
59k
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1
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Pin Descriptions
Pin #
Symbol
Function
1
2, 8, 10, 18,
19
INL1
I
3
ENL1
I
4
INBK
I
5
6
7
LX
PGND
ENBK
I/O
9
FB
I
11
ENL2
I
12
ENL3
I
13,17
14
15
16
20
EP
AGND
OUTL3
OUTL2
INL2
OUTL1
GND
O
O
I
O
N/C
Description
Power input for LDO1. Connect a 2.2μF capacitor between this pin and ground.
Not Connected
I
Active high enable pin. When pulled high, LDO1 regulates its output to the programmed
voltage value.
Power input pin for the switching converter. Connect a 4.7μF capacitor between ground and
INBK.
DC/DC step-down converter switching node. Connect LX to the terminal of the inductor.
DC/DC converter power ground.
Active high step-down DC/DC converter enable pin.
DC/DC converter output feedback pin. Connect to a resistor divider for an adjustable output voltage.
Active high enable pin. When pulled high, LDO2 regulates its output to the programmed
voltage value.
Active high enable pin. When pulled high, LDO3 regulates its output to the programmed
voltage value.
Analog ground.
LDO3 output. Connect a 1μF capacitor between the pin and ground.
LDO2 output. Connect a 1μF capacitor between the pin and ground.
Power input for LDO2/3. Connect a 2.2μF capacitor between the pin and ground.
LDO1 output. Connect a 1μF capacitor between the pin and ground.
Exposed pad.
Pin Configuration
2
OUTL1
N/C
N/C
AGND
INL2
TQFN33-20
(Top View)
20
19
18
17
16
2
14
OUTL3
ENL1
3
13
AGND
INBK
4
12
ENL3
LX
5
11
ENL2
6
7
8
9
10
N/C
N/C
FB
OUTL2
N/C
15
ENBK
1
PGND
INL1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Absolute Maximum Ratings1
Symbol
Description
Value
INL1, INL2, INBK, OUTL1, OUTL2, OUTL3
ENL1, ENL2, ENL3
ENBK, FB
LX to PGND
PGND to AGND, AGND to AGND
Operating Ambient Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at leads, 10 sec.)
TA
TS
TLEAD
-0.3 to 6.0
-0.3 to 6.0
-0.3 to VINBK
-0.3 to VINBK
-0.3 to +0.3
-40 to 85
-65 to 150
300
Units
V
°C
Thermal Information2
Symbol
θJA
PD
Description
Thermal Resistance
Maximum Power Dissipation
3
Value
Units
50
2
°C/W
W
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.
2. Mounted on an FR4 board.
3. Thermal Resistance measured with the device on multi-layer evaluation board in a thermal oven. The amount of power dissipation which will cause the thermal shutdown to
activate will depend on the ambient temperature and the PC board layout ability to dissipate the heat. De-rate 30mW/°C above 70°C.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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3
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Electrical Characteristics1
VINBK = VINL1 = VINL2 = 3.6V, L = 2.2μH, CINL1, 2 = 2.2μF, CINBK = 4.7μF, COUTBK = 10μF, COUTL1, 2, 3 = 1μF, TA= 25°C unless
otherwise noted.
Symbol
Description
PMU Operation
VIN
Input Voltage
Under-Voltage
UVLO
Lockout
TSD
Thermal Shutdown
Quiescent Current
IQ
Logic Control
Input Logic High
VIH
Threshold
Input Logic Low
VIL
Threshold
DC-DC Step-Down Converter
Shutdown Current
ISHDN
from INBK Pin
IQ
Quiescent Current
P-Channel Current
ILIM
Limit
Output Voltage
VOUT
Range
Feedback Voltage
VFB_ACC
Accuracy
Operating SwitchfSW
ing Frequency
High-Side Switch
RDS(ON)H
On Resistance
RDS(ON)L
LDO
ISHDN
ILIM
VDROP
VOUTL_ACC
ΔVOUTL/
IOUTL
VOUTL/
VINL
Low-Side Switch
On Resistance
Shutdown Current
Output Current
Limit
Dropout Voltage
Output Voltage
Accuracy
Conditions
Min
2.5
Rising
Hysteresis
Threshold
Hysteresis
VENBK > 1.5V, VENL1,2,3 >1.5V, no load
1.5
ENL1, ENL2, ENL3, ENBK
4
5.5
420
V
V
mV
°C
°C
μA
VINBK
V
0.4
V
1
μA
VENL 1, 2, 3 < 0.4V , VENBK >1.5V , IOUTB = 0mA
120
280
μA
VINBK = 2.7V to 5.5V
800
mA
0.9
TA = -40°C to 85°C
0.585
0.600
85%∙VINBK
V
0.615
V
1.5
IOUTB
IOUTB
IOUTB
IOUTB
=
=
=
=
200mA
200mA, VINBK = 2.5V
200mA
200mA, VINBK = 2.5V
RLOAD = 1Ω
450
IOUTL = 300mA
TA = -40°C to 85°C, 1mA load
Line Regulation
VINL1 = VINL2 = 2.7V to 5.5V
COUT1,2,3 = 1μF,
VINL = VOUTL1,2,3 + 1V
-3
0.3
f = 1kHz
MHz
230
280
180
220
VENBK = VENL < 0.4V
1mA < IOUTL < 300mA
Output Voltage
Temperature Coefficient
Units
0.1
f = 10kHz
VOUTL_TC
Max
VENBK < 0.4V, VENL 1, 2, 3 < 0.4V
Load Regulation
Power Supply
Rejection Ratio
1.9
150
140
15
220
ENL1, ENL2, ENL3, ENBK
f = 100Hz
PSRR
Typ
IOUT = 10mA
IOUT = 150mA
IOUT = 10mA
IOUT = 150mA
IOUT = 10mA
IOUT = 150mA
mΩ
mΩ
1
μA
600
mA
500
mV
3
%
0.6
%
0.2
%/V
75
75
70
70
50
50
dB
100
ppm/°C
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
DATA
SHEET
PRODUCT
DATASHEET
AAT2612
AAT2612
SwitchRegTM
Step-Down DC/DC
DC/DC Converter
Converter With
WithThree
Three High
High PSRR
PSRR LDOs
LDOs
Step-Down
Supply Current vs Supply Voltage
Buck Quiescent Current vs Supply Voltage
(VOUT= 1.2V, VENB> 1.5V,VENL< 0.4V)
250
140.00
230
130.00
IQ (μA)
Supply Current (μA)
(VENB, VENL> 1.5V)
120.00
210
110.00
190
85°C
170
100.00
85°C
25°C
-40°C
25°C
-40°C
150
2.5
3.0
3.5
4.0
4.5
5.0
90.00
2.5
5.5
3.0
3.5
Switching Frequency vs Temperature
Switching Frequency (MHz)
Switching Frequency (MHz)
5.5
(VOUTB = 1.2V, IOUTB = 600mA)
1.60
1.55
1.50
1.45
1.40
1.35
10
5.0
Switching Frequency vs Input Voltage
(VINB = 3.6V, IOUT = 600mA)
-15
4.5
Supply Voltage (V)
Supply Voltage (V)
-40
4.0
35
60
1.54
1.52
1.50
1.48
1.46
1.44
85
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
Temperature (°C)
Buck Efficiency vs Output Current
UVLO Volatge vs Temperature
(VOUT = 1.2V; L = 2.2μH)
1.950
100
90
1.910
VEOC (V)
Efficiency (%)
80
70
60
50
1.870
1.830
40
VIN = 2.5V
30
VIN = 3.6V
1.790
VIN = 4.2V
20
VIN = 5.0V
10
UVLO_H
VIN = 5.5V
UVLO_L
0
0.1
1
10
Output Current (mA)
100
1000
1.750
-40
-15
10
35
60
85
Temperature (°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
5
DATA
SHEET
PRODUCT
DATASHEET
AAT2612
AAT2612
SwitchRegTM
Step-Down DC/DC
DC/DC Converter
Converter With
WithThree
Three High
High PSRR
PSRR LDOs
LDOs
Step-Down
Buck Output Voltage vs Temperature
Buck Line Regulation
(VINB= 3.6V; VOUTB = 1.2V; L = 2.2μH)
(VOUT = 1.2V; L = 2.2μH)
1
1.000
0.8
VOUT Error (%)
Output Error (%)
0.600
0.200
-0.200
-0.600
0.6
0.4
0.2
0
-0.2
-0.4
IOUT = 10mA
-0.6
IOUT = 100mA
IOUT = 300mA
-0.8
IOUT = 600mA
-1
-1.000
-40
-15
10
35
60
2.5
85
3
Temperature (°C)
3.5
4
4.5
5
5.5
Input Voltage (V)
Buck Load Regulation
EN VIH vs Supply Voltage
(VOUT = 1.2V; L = 2.2μH)
1.20
1
EN VIH (V)
Output Error (%)
0.8
0.6
0.4
0.2
0
1.10
1.00
0.90
-0.2
-0.4
VIN = 2.5V
VIN = 3.6V
-0.6
0.80
VIN = 4.2V
-40°C
VIN = 5.0V
-0.8
25°C
VIN = 5.5V
85°C
0.70
-1
10
70
130
190
250
310
370
430
490
550
610
2.5
Output Current (mA)
3.0
3.5
4.0
4.5
Supply Voltage (V)
EN VIL vs Supply Voltage
Softstart
(VIN = 3.6V; VOUTB = 1.2V; IOUTB = 600mA)
1.20
EN VIL (V)
1.10
VIN
2V/div
1.00
0.90
VOUT
1V/div
0
0
0.80
0.70
IIN
-40°C
0.2A/div 0
25°C
85°C
0.60
2.5
3.0
3.5
4.0
4.5
Supply Voltage (V)
6
5.0
5.5
Time 40 μS/div
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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5.0
5.5
DATA
SHEET
PRODUCT
DATASHEET
AAT2612
AAT2612
SwitchRegTM
Step-Down DC/DC
DC/DC Converter
Converter With
WithThree
Three High
High PSRR
PSRR LDOs
LDOs
Step-Down
Buck Load Transient
Buck Line Transient
(VIN = 3.6V, VOUTB = 1.2V, CINB = 10μF, COUTB = 10μF)
(VINB = 4V to 5V, IOUTB = 600mA)
VOUTB
1.2
200mV/div
VIN
1V/div
4
600mA
IOUTB
400mA
0.2A/div
VOUT
50mV/div
1.2
0A
Time 40 μS/div
Output Ripple
LDO Output Voltage vs Temperature
(VIN = 3.6V; VOUT = 1.2V; IOUT = 600mA; CINB = 4.7μF)
(VIN = 3.6V)
0.600
LDO1
0.400
VOUT
20mv/div 1.2
LDO2
VOUT Error (%)
LDO3
0.200
0.000
-0.200
VLX
2V/div
0
-0.400
-0.600
-40
-15
Time 0.4 μS/div
10
35
60
85
Temperature (°C)
LDO Quiescent Current vs Supply Voltage
LDO Line Regulation
(Single Channel)
(VOUTL = 1.8V)
34.00
0.1
0.08
Output Error (%/V)
IQ (μA)
32.00
30.00
28.00
85°C
25°C
26.00
-40°C
0.06
0.04
0.02
0
-0.02
-0.04
IOUTB = 10mA
-0.06
IOUTB = 100mA
-0.08
IOUTB = 200mA
IOUTB =300mA
24.00
2.5
3.0
3.5
4.0
4.5
Supply Voltage (V)
5.0
5.5
-0.1
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
7
DATA
SHEET
PRODUCT
DATASHEET
AAT2612
AAT2612
SwitchRegTM
Step-Down DC/DC
DC/DC Converter
Converter With
WithThree
Three High
High PSRR
PSRR LDOs
LDOs
Step-Down
Dropout Voltage vs Load Current
LDO Load Transient
(VOUT = 2.8V)
(VIN = 3.6V, VOUTL = 1.8V, CINL = 2.2μF, COUTL = 1μF)
Dropout Voltage(mV)
350
300
250
VOUTL
1.8
200mV/div
200
150
300mA
100
85°C
25°C
50
IOUTL
-40°C
0.2A/div
0A
0
20
60
100
140
180
220
260
300
Load Current (mA)
Time 100 μS/div
LDO Line Transient
LDO1 Power Supply Rejection Ratio, PSRR
(VINB = 4V to 5V, IOUTL = 300mA)
(IOUT1 = 10mA, BW = 100~100KHz)
100
90
VIN
1V/div
Magnitude (dB)
80
4
VOUT
20mV/div 2.8
70
60
50
40
30
20
10mA
10
0
100
Time 20 μs/div
8
1000
10000
Frequency (Hz)
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100000
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Block Diagram
INBK 4.7uF
Buck
ENBK
INL2
LX
2.2uH
1.2V, 600mA
Control
4.7uF
PGND
1uF
FB
INL1
R2
59k
Bias, Control, and OTP, Thermal
Shutdownd
1uF
R1
59k
ENL3
LDO 3
OUTL3
1.8V. 300mA
1uF
ENL2
LDO 2
LDO 1
ENL1
OUTL2
2.8V, 300mA
1uF
OUTL1
2.8V. 300mA
1 uF
AGND
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
9
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Functional Description
The AAT2612 is a compact power management solution.
It integrates a step-down converter with three high PSRR
low-dropout regulators to provide power from a wall
adapter, USB port, or a single-cell Lithium Ion/Polymer
battery or dual cell alkaline battery.
The AAT2612 uses fixed-frequency peak current control
architecture. Light load mode is used to enhance light
load efficiency. Compensation is integrated to reduce the
number of external components and achieve excellent
transient response and load/line regulation.
The ideal 1.5MHz switching frequency allows the use of
smaller output filter components for improved power
density, reduced external component size, and optimized
output voltage ripple.
The AAT2612 has four separate enable pins to control
buck converter and three LDO regulator outputs’ startup.
Also see the “Enable Function” section in the Applications
Information section of this datasheet.
Synchronous Step-Down Converter
The AAT2612 contains one high performance 600mA,
1.5MHz synchronous step-down converter. The stepdown converter operates to ensure high efficiency performance over all load conditions.
The input voltage range is from 2.5V to 5.5V, and the
output voltage is programmable from 85% of VIN to as
low as 0.9V with external resistor divider. Power devices
are sized for 600mA current capability while maintaining
over 85% efficiency at full load. High efficiency is maintained at lower currents
A high DC gain error amplifier with internal compensation controls the output. It provides excellent transient
response and load/line regulation. The converter has soft
start control to limit inrush current.
Apart from the resistor divider and input capacitor, only
a small L-C filter is required at the output side for the
step-down converter to operate properly. Typically, a
2.2μH inductor and a 10μF ceramic capacitor are recommended for low output voltage ripple and small component size.
Control Loop
The converter is a peak current mode step-down converter. The inner, wide bandwidth loop controls the
inductor peak current. The inductor current is sensed
through the P-channel MOSFET (high side) and is also
10
used for 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
inductor current to force a constant output voltage for all
load and line conditions. The voltage feedback resistive
divider is external and the error amplifier reference voltage is 0.6V. The voltage loop has a high DC gain making
for excellent DC load and line regulation. The internal
voltage loop compensation is located at the output of the
transconductance voltage error amplifier.
Soft-Start
Soft start increases the inductor current limit point linearly when the input voltage or enable input is applied.
It limits the current surge seen at the input and eliminates output voltage overshoot.
Current Limit and
Over-Temperature Protection
For overload conditions the peak input current is limited.
As load impedance decreases and the output voltage
falls closer to zero, more power is dissipated internally,
raising the device temperature. Thermal protection completely disables switching when internal dissipation
becomes excessive, protecting the device from damage.
The junction over-temperature threshold is 140°C with
15°C of hysteresis.
LDO Regulator
The advanced circuit design of the linear regulator is
specifically optimized for very fast start-up and shutdown timing. This proprietary LDO is also tailored for
superior transient response characteristics. These traits
are particularly important for applications which require
fast power supply timing.
The high-speed turn-on capability is enabled through the
implementation of a fast start control circuit, which
accelerates the power up behavior of fundamental control and feedback circuits within the LDO regulator. Fast
turn-off time response is achieved by an active output
pull down circuit, which is enabled when the LDO regulator is placed in the shutdown mode. This active fast
shutdown circuit has no adverse effect on normal device
operation. The LDO regulator output has been specifically optimized to function with low cost, low ESR ceram-
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
ic capacitors. However, the design will allow for operation over a wide range of capacitor types.
The regulator comes with complete short circuit and thermal protection. The combination of these two internal
protection circuits gives a comprehensive safety system
to guard against extreme adverse operating conditions.
Application Information
The proper placement of the input capacitors (C1, C2,
and C3) is shown in the evaluation board layout in Figure
2.
Step-down Converter
Input Capacitor
Select a 4.7uF to 10uF X7R or X5R ceramic capacitor for
the input. To estimate the required input capacitor value
and size, determine the acceptable input ripple voltage
level (Vpp) and solve for CIN. The calculated value varies
with input voltage and is a maximum when VIN is double
the output voltage.
CIN =
V
VO
· 1- O
VIN
VIN
VPP
- ESR · fS
IO
1
VPP
- ESR · 4 · fS
IO
Where CIN is the input capacitance, VIN is
age, VO is the output voltage, fS is the
quency, IO is the output current, ESR is
series resistor of output capacitor, and
cycle.
Output Capacitor
the input voltswitching frethe equivalent
D is the duty
The maximum input capacitor RMS current is:
IRMS = IO ·
VO
V
· 1- O
VIN
VIN
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 =
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 can also result in the loop
phase and gain measurements. 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 capacitor should be placed in parallel
with the low ESR/ESL bypass ceramic capacitor. This
dampens the high Q network and stabilizes the system.
VO
D= V
IN
CIN(MIN) =
The input capacitor provides a low impedance loop for
the edges of pulsed current drawn by the AAT2612. Low
ESR/ESL X7R and X5R ceramic capacitors are ideal for
this function. To minimize parasitic inductances, 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.
IO
2
The maximum input voltage ripple also appears at 50%
duty cycle.
The output capacitor limits the output ripple and provides holdup during large load transitions. A typical
4.7μF 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.
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 · ΔILOAD
VDROOP · FS
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11
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
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.
Output Inductor
For most designs, the AAT2612 operates with inductor
values of 2.2μH to 4.7μH. Inductors with low inductance
values are physically smaller but generate higher inductor current ripple leading to higher output voltage ripple.
The inductor value can be derived from the following
equation:
L=
VOUT · (VIN - VOUT)
VIN · ∆IL · fOSC
Where ΔIL is inductor ripple current. Large value inductors result in lower ripple current and small value inductors result in high ripple current. Choose inductor ripple
current approximately 30% of the maximum load current 0.6A, or
∆IL = 180mA
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
appreciable saturation under normal load conditions. The
DC current rating of the inductor should be at least equal
to the maximum load current plus half the inductor ripple current to prevent core saturation (0.6A + 180mA).
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.
Feedback Resistor Selection
The Buck output voltage on the AAT2612 is adjustable
with external resistors R1 and R2 which program the
output to regulate at a voltage in the range of 0.9V to
0.85 ∙ VINBK. To limit the bias current required for the
external feedback resistor string while maintaining good
noise immunity, the minimum suggested value for R2 is
59kΩ. 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. The maximum value of R1 should
be below 1Mohm to keep reference voltage normal and
avoid noise coupling.
12
R1 =
VOUT
VOUT
- 1 · R2 =
- 1 · R2
VREF
0.6V
Table 1 shows the standard 1% metal film resistor values
for different step-down output voltages
VOUT (V)
R2 = 59kΩ,
R1 (kΩ)
1.2
2.8
3.3
3.6
4.2
59
216
265.5
259
354
Table 1: VOUT Resistor Selection
Enable Function
The AAT2612 features one buck output enable/disable
function for buck converter. This pin (ENBK) is active
high and is compatible with CMOS logic. To assure the
buck output will switch on, the ENBK turn-on control
level must be greater than 1.5V. The buck converter will
go into the disable shutdown mode when the voltage on
the ENBK pin falls below 0.6V. If the enable function is
not needed in a specific application, it may be tied to VIN
to keep the buck output in a continuously on state.
Low Dropout Regulator
Input Capacitor
Typically, a 2.2μF or larger capacitor is recommended for
CIN in most applications. A CIN capacitor is not required
for basic LDO regulator operation. However, if the LDO is
physically located any distance more than one or two
centimeters from the input power source, a CIN capacitor
will be needed for stable operation. CIN should be located
as closely to the device VINL pin as practically possible.
CIN values greater than 1μF will offer superior input line
transient response and will assist in maximizing the
power supply ripple rejection.
Ceramic, tantalum, or aluminum electrolytic capacitors
may be selected for CIN as there is no specific capacitor
ESR requirement. For better performance, ceramic
capacitors are recommended for CIN due to their inherent
capability over tantalum capacitors to withstand input
current surges from low impedance sources such as batteries in portable devices.
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DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Output Capacitor
For proper load voltage regulation and operational stability, a capacitor is required between pins VOUT and
GND. The COUT capacitor connection to the LDO regulator
ground pin should be made as direct as practically possible for maximum device performance. The AAT2612
LDOs have been specifically designed to function with
very low ESR ceramic capacitors. Although the device is
intended to operate with these low ESR capacitors, it is
stable over a very wide range of capacitor ESR, thus it
will also work with some higher ESR tantalum or aluminum electrolytic capacitors. For best performance,
ceramic capacitors are recommended.
The value of COUT typically ranges from 1μF to 10μF. 1μF
is sufficient for most operating conditions.
Enable Function
stand indefinite short-circuit conditions without sustaining permanent damage.
No-Load Stability
The AAT2612 LDO is designed to maintain output voltage
regulation and stability under operational no-load conditions. This is an important characteristic for applications
where the output current may drop to zero. An output
capacitor is required for stability under no-load operating
conditions. Refer to the Output Capacitor section of this
datasheet for recommended typical output capacitor values.
Internal Power Supply
The AAT2612 internal circuitry uses INL1 as the internal
power supply. The buck output will have no output when
INL1 is not connected to power.
Thermal Calculations
The AAT2612 features three LDO regulator enable/disable function for LDO1/2/3 respectively. These pins
(ENL1, ENL2, and ENL3) are active high and are compatible with CMOS logic. To assure the LDO regulator will
switch on, the EN turn-on control level must be greater
than 1.5V. The LDO regulator will go into the disable
shutdown mode when the voltage on the EN pin falls
below 0.6V. If the enable function is not needed in a
specific application, it may be tied to VIN to keep the LDO
regulator in a continuously on state.
There are three types of losses associated with the
AAT2612 step-down converters: 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, with continuous conduction
mode (CCM), a simplified form of the losses is given by:
Short-circuit and Thermal Protection
VO
VO
PBUCK = IO2 · RDS(ON)P · V + RDS(ON)N · 1 - V
IN
IN
The AAT2612 LDOs are protected by both current-limiting
and over-temperature protection circuitry. The internal
short-circuit current limiting circuit is designed to activate
when the output load demand exceeds the maximum
rated output. If a short-circuit condition were to continually draw more than the current limit threshold, the LDO
regulator’s output voltage would drop to a level necessary
to supply the current demanded by the load. Under shortcircuit or other over-current operating conditions, the
output voltage would drop and the AAT2612’s die temperature would rapidly increase. Once the regulator’s
power dissipation capacity has been exceeded and the
internal die temperature reaches approximately 140°C,
the system thermal protection circuit will become active.
The internal thermal protection circuit will actively turn off
the LDO regulator output pass device to prevent the possibility of over-temperature damage. The LDO regulator
output will remain in a shutdown state until the internal
die temperature falls back below the 140°C trip point.
The interaction between the short-circuit and thermal
protection systems allows the LDO regulator to with-
+ tSW · fS · IO · VIN + IQ · VIN
Where IQ is the step-down converter quiescent current,
tsw is the switching time, RDS(ON)P and RDS(ON)N are the high
side and low side switching MOSFETs’ on-resistance. VIN,
VO and IO are the input voltage, the output voltage and
the load current.
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.
For all the LDOs,
PD(MAX) = (VIN – VOUT) · IOUT(MAX).
The total power losses of both step-down converter and
LDOs can be expressed as
PTOTAL = PBUCK + PD(MAX).
Given the total losses, the maximum junction temperature can be derived from the θJA for the package.
TJ(MAX) = PTOTAL · θJA + TA
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13
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Layout Considerations
The suggested PCB layout for the AAT2612 is shown in
Figures 2(a) - 2(d). The following guidelines are recommended to ensure a proper layout:
1.
2.
3.
of L1 to the LX pins as short as possible and route
no signal lines under the inductor.
Separate the feedback traces or FB pin (Pin 9) 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.
Keep the resistance of the trace from the load
returns to PGND 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.
Connect the ground pin of the exposed pad to AGND
internal plane with multiple vias to decrease the
effect of large power ground PGND noise on the analog ground.
Connect the ground pins of LDO output capacitors to
AGND.
4.
Connect the input capacitors (C1, C2, C3) and output capacitors (C5, C6, C7, C8 ) as close as possible
to the pins (INL1, INL2, INBK, VOUT) and power
ground (AGND, PGND) to minimize any parasitic
inductance in the switched current path which generates a large voltage spike during the switching
interval.
Keep the power traces (GND, LX, and INBK) short,
direct, and wide to allow large current flow. Place
sufficient multiple-layer pads when needed to change
the trace layer.
Connect the output capacitor C8 and inductor L1 as
close as possible to the device. Keep the connection
5.
6.
7.
U1
AAT2612
INL1
2.5V to 5.5V
1
INL1
C1
2.2μF
J_IN1
INL2
2.5V to 5.5V
16
INL2
OUTL1
20
LDO1
LDO1
LDO2
LDO2
LDO3
LDO3
L1
BO1
1.2V 600mA
C5
1μF
C2
2.2μF
J_IN2
INBK
2.5V to 5.5V
4
INBK
OUTL2
C3
4.7μF
C6
1μF
2
ENL1
3
ENL2 ENL2
11
ENL3 ENL3
12
13
17
OUTL3
14
C7
1μF
ENL1
ENL2
LX
ENL3
AGND
AGND
FB
PGND
5
LX
2.2μH
9
FB
6
PGND
R1
C4
59k
N/C
C8
10μF
0
AGND
ENBK
N/C
EP
ENBK 7
ENBK
ENL1
15
R2
59k
GND
Figure 1: AAT2612IDG Evaluation Board Schematic.
14
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DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
a: Top Side
b: Internal Plane 1 (AGND)
c: Internal Plane 2 (PGND)
d: Bottom Side
Figure 2: AAT2612IDG Evaluation Board Layout.
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15
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Component
Part Number
Description
Manufacturer
U1
C1, C2
C3
C8
C4, C5, C6, C7
L1
R1, R2
AAT2612
GRM188R71A225KE15
GRM188R60J475KE19
GRM188R60J106ME47
GRM188R71C105KA12
LQH3NPN2R2MM0
RC0603FR-0759KL
Step-Down DC/DC Converter with Three High PSRR LDOs
Cap Ceramic 2.2μF 0603 X7R 10V 10%
Cap Ceramic 4.7μF 0603 X5R 6.3V 10%
Cap Ceramic 10μF 0603 X5R 6.3V 10%
Cap Ceramic 1μF 0603 X7R 6.3V 10%
2.2μH, 73mΩ, 1.25A, 20%
Res, 59kΩ, 1/10W, 1%, 0603, SMD
Skyworks
Murata
Yageo
Table 2: AAT2612IDG Evaluation Board Bill of Materials (BOM).
Manufacturer
Murata
Coilcraft
Part Number
L (μH)
Max DCR (mΩ)
Saturation Current (A)
LQH3NP2R2NG0
LQH3NP3R3NG0
LQH3NP4R7NG0
LPA3015-222MLC
LPA3015-332MLC
LPA3015-472MLC
2.2
3.3
4.7
2.2
3.3
4.7
140
180
260
110
130
200
1.27
0.85
0.8
1.1
1.1
0.9
Size WxLxH (mm)
3.0x3.0x0.9
3.1x3.1x1.5
Table 3: Surface Mount Inductors.
Manufacturer
Murata
AVX
KEMET
Part Number
Value (μF)
Voltage (V)
Tolerance
Temp.
Co.
Case
GRM188R70J105K
GRM188R70J106K
GRM188R71A225K
GRM188R71A475K
06036C105KAT
06036C106KAT
0603ZC225KAT
0603ZC475KAT
C0603C105K9RAC
C0603C106K9RAC
C0603C225K8RAC
C0603C475K8RAC
1
10
2.2
4.7
1
10
2.2
4.7
1
10
2.2
4.7
6.3
6.3
10
10
6.3
6.3
10
10
6.3
6.3
10
10
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
X7R
X7R
X7R
X7R
X7R
X7R
X7R
X7R
X7R
X7R
X7R
X7R
0603
0603
0603
0603
0603
0603
0603
0603
0603
0603
0603
0603
Table 4: Surface Mount Capacitors.
16
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DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Ordering Information
DC-DC Step-Down
(V)
LDO1
(V)
LDO2
(V)
LDO3
(V)
Part Marking1
Part Number (Tape and Reel)2
Adj
Adj
Adj
Adj
Adj
Adj
2.8
2.8
2.8
2.8
2.8
3.0
2.8
1.8
2.8
1.8
1.8
1.8
1.8
1.8
2.8
3.0
3.3
3.3
S2XYY
TBD
TBD
TBD
T5XYY
T6XYY
AAT2612IDG-1-T1
AAT2612IDG-2-T1
AAT2612IDG-3-T1
AAT2612IDG-4-T1
AAT2612IDG-5-T1
AAT2612IDG-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
TQFN33-203
3.00 ± 0.05
1.700 ± 0.050
Index Area
0.400 BSC
1.700 ± 0.050
Detail "A"
0.400 ± 0.050
3.00 ± 0.05
R(5x)
Top View
(Saw Type)
Bottom View
0.210 ± 0.040
0.75 ± 0.05
Detail "A"
0
+ 0.10
-0.00
0.203 REF
Side View
(Saw Type)
All dimensions in millimeters.
1. A = assembly house code, Y = year, W = week.
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 the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection
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17
DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Copyright © 2012, 2013 Skyworks Solutions, Inc. All Rights Reserved.
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