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AAT2503
Adjustable 3-Channel Regulator General Description
The AAT2503 is a three-channel regulator consisting of a step-down converter with an input voltage range of 2.7V to 5.5V plus two low dropout (LDO) linear regulators. The step-down converter optimizes power efficiency throughout the load range. Pulling the MODE/ SYNC pin high enables "PWM Only" mode, maintaining constant frequency and low output ripple across the operating range. Alternatively, the converter may be synchronized to an external clock input to the MODE/SYNC pin. The step-down converter delivers up to 800mA of output current, while consuming 30A of typical no load quiescent current. The switching frequency is 2MHz, minimizing the size of external components. The two LDOs (LDOA/LDOB) have independent inputs and are capable of delivering up to 150mA each. A Power-OK (POK) function provides an open drain output signal when LDOA is within regulation. Both LDOs feature low quiescent current and a low dropout voltage. The output voltages for both LDOs are adjustable to as low as 0.6V. The linear regulators have independent Enable pins. The AAT2503 is available in a Pb-free 3x4mm QFN34-20 package and is rated over the -40C to +85C temperature range.
Features
*
SystemPowerTM
*
* * * * * *
800mA Step-Down Converter -- VIN Range: 2.7V to 5.5V -- VOUT Range: 0.9V to VIN -- High Efficiency -- 2MHz Switching Frequency Two 150mA Low Dropout Regulators -- VOUT Range: 0.6V to VIN -- High Output Accuracy: 1.5% 85A of Total IQ Independent Enable Pins Integrated Power MOSFETs Over-Temperature and Current Limit Protection QFN34-20 Package -40C to +85C Temperature Range
Applications
* * * * * Cellular Phones Digital Cameras Handheld Instruments Microprocessor/DSP Core/IO Power PDAs and Handheld Computers
Typical Application
L1 LX
AAT2503
VIN VIN VLDOA VLDOB VP MODE/SYNC ENA ENB EN
VOUT (Buck)
FB
OUTA R3 100k POK FBA OUTB OUTB POK
R1 R4
OUTA C2 10F
R5
FBB
R8
PGND AGND
C6 2.2F
R7
C5 2.2F
R2
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AAT2503
Adjustable 3-Channel Regulator Pin Descriptions
Pin #
1
Symbol
FBB
Function
Feedback input pin for LDOB. This pin is connected to OUTB via an external resistor. It is used to see the output of LDOB to regulate to the desired value via an external resistor divider. For fixed versions, short FBB to OUTB. Enable pin for LDOA. When connected low, LDOA is disabled and consumes less than 1A of current. When connected high, normal operation. Enable pin for LDOB. When connected low, LDOB is disabled and consumes less than 1A of current. When connected high, normal operation. Connect to ground for PWM/PFM mode and optimized efficiency throughout the load range. Connect high for low noise PWM operation under all operating conditions. Connect to an external clock for synchronization (PWM only). Feedback input pin for the step-down converter. This pin is connected to the converter output via an external resistor. It is used to see the output of the converter to regulate to the desired value via an external resistor divider. Ground connection pin. Main power ground return pin for the step-down converter. Connect to the output and input capacitor return. Connect inductor to this pin. Switching node internally connected to the drain of both highand low-side MOSFETs. Input supply voltage for the converter. Must be closely decoupled. Not connected. Bias supply. Supply power for the internal circuitry. Connect to input power via low pass filter with decoupling to AGND. Enable for the step-down converter. A logic low disables the converter and it consumes less than 1A of current. A logic high enables normal operation. Power-OK pin with open drain output. It is pulled low when the OUTA pin is outside the regulation window of 10%. Place a pull-up resistor between POK and OUTA. Feedback input pin for LDOA. This pin is connected to OUTA via an external resistor. It is used to see the output of LDOA to regulate to the desired value via an external resistor divider. For fixed versions, short FBA to OUTA. LDOA output pin; should be closely decoupled with a low-ESR ceramic capacitor. Input voltage pin for linear regulator A; should be closely decoupled. Input voltage pin for linear regulator B; should be closely decoupled. LDOB output pin; should be closely decoupled with a low-ESR ceramic capacitor. Exposed paddle; connect to ground directly beneath the package.
2 3 4
ENA ENB MODE/SYNC
5
FB
6 7 8, 9 10 11, 12 13 14 15 16
AGND PGND LX VP N/C VIN EN POK FBA
17 18 19 20 EP
OUTA VLDOA VLDOB OUTB
2
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AAT2503
Adjustable 3-Channel Regulator Pin Configuration
QFN34-20 (Top View)
OUTA VLDOA VLDOB OUTB
20 19 18 17
FBB ENA ENB MODE/SYNC FB AGND
1 2 3 4 5 6
16 15 14 13 12 11
FBA POK EN VIN N/C N/C
10
9
7
8
VP LX LX PGND
Absolute Maximum Ratings1
Symbol
VP, VIN, VLDO VLX VFB VN TJ TLEAD
Description
Input Voltage and Bias Power to GND LX to GND FB to GND EN, MODE/SYNC to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
6.0 -0.3 to VP + 0.3 -0.3 to VP + 0.3 -0.3 to 6.0 -40 to 150 300
Units
V V V V C C
Thermal Information
Symbol
PD JA
Description
Maximum Power Dissipation (TA = 25C) Thermal Resistance2
Value
2.0 50
Units
W C/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. Only one Absolute Maximum Rating should be applied at any one time. 2. Mounted on an FR4 board. 2503.2007.04.1.1
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AAT2503
Adjustable 3-Channel Regulator Electrical Characteristics1
VIN = 3.6V; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol Description Conditions
ENA = ENB = EN = VIN; ILOAD = 0 ENA = ENB = EN = GND
Min Typ Max
85 145 1.0
Units
A A V % V mV %/V V V mA mA A C C
Bias Power Supply IQ Quiescent Current ISHDN Shutdown Current LDOA, LDOB; IOUT = 150mA VLDO Input Voltage VOUT VFB VDO VOUT/ VOUT*VIN VEN(L) VEN(H) IOUT ISC ISHT TSD THYS LDOA; IOUT VPOK VPOKHYS VPOK(LO) IPOK Output Voltage Tolerance Feedback Voltage Dropout Voltage2 Line Regulation3 Enable Threshold Low Enable Threshold High Output Current Short-Circuit Current Shutdown Current Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis = 150mA Power-OK Trip Threshold Power-OK Hysteresis Power-OK Output Voltage Low Power-OK Output Leakage Current
IOUT = 1mA to 150mA IOUT = 150mA
TA = 25C TA = -40C to +85C
2.8 5.5 -1.5 1.5 -2.5 2.5 0.593 0.6 0.607 150 0.09 0.6 1.4 150
VIN = VOUT + 1 to 5.0V
VOUT < 0.4V VIN = 5V
300 1.0 140 15
VOUT Rising, TA = 25C ISINK = 1mA VPOK <5.5V, VOUT in Regulation
90
94 1.0
98 0.4 1.0
% of VOUT % of VOUT V A
1. The AAT2503 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. VDO is defined as VIN - VOUT when VOUT is 98% of nominal. 3. CIN = 10F.
4
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AAT2503
Adjustable 3-Channel Regulator Electrical Characteristics (continued)1
VIN = 3.6V; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol Description Conditions Min
2.7 VIN Rising Hysteresis VIN Falling IOUT = 0 to 800mA; VIN = 2.7V to 5.5V 250 1.5 -3.0 0.9 0.891 EN = GND VIN = 5.5, VLX = 0 to VIN VFB = 1.0V 1.2 400 300 0.5 0.2 1.6 2.0 140 15 0.6 VEN = 5V, VIN = 5V 1.4 -1.0 1.0 VIN x 0.4 2.4 3.0 VIN 0.909 1.0 1.0 0.2
Typ
Max
5.5 1.8
Units
V V mV V % V V A A A A m m % %/V MHz C C V V A V V
Step-Down Converter; IOUT = 800mA VIN Input Voltage UVLO Under-Voltage Lockout Voltage
VOUT VOUT VFB ISHDN ILX_LEAK IFB ILIM RDS(ON)H RDS(ON)L VOUT/VOUT VOUT/ VOUT*VIN FOSC TSD THYS VEN(L) VEN(H) IEN VMODE/SYNC(L) VMODE/SYNC(H) IMODE/SYNC
Output Voltage Tolerance VOUT Programmable Range Feedback Threshold Voltage Shutdown Current LX Leakage Current Feedback Leakage Current Limit High Side Switch On Resistance Low Side Switch On Resistance Load Regulation Line Regulation Oscillator Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High EN Input Leakage Enable Threshold Low Enable Threshold High Input Low Current
0.9
ILOAD = 0 to 800mA
VIN x 0.7 -1.0
1.0
A
1. The AAT2503 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2503.2007.04.1.1
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AAT2503
Adjustable 3-Channel Regulator Typical Characteristics--Step-Down Converter
Efficiency vs. Output Current
(VOUT = 2.5V; L = 3.3H)
100 90 80 100 90 80
Efficiency vs. Output Current
(VOUT = 1.8V; L = 2.2H)
VIN = 3.6V VIN = 2.7V PWM Only Mode
Efficiency (%)
70 60 50 40 30 20 10 0 0
VIN = 3.3V VIN = 3.6V VIN = 4.2V PWM Only Mode
Efficiency (%)
70 60 50 40 30 20 10 0
VIN = 4.2V
1
10
100
1000
0
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Output Current
(VOUT = 0.9V; L = 1H)
90 80 2.4 2.3
Switching Frequency vs. Temperature
(VIN = 3.6V; IOUT = 800mA)
Efficiency (%)
70 60 50 40 30 20 10 0 0 1
Frequency (MHz)
VIN = 2.7V VIN = 3.6V VIN = 4.2V PWM Only Mode
2.2 2.1 2.0 1.9 1.8 1.7 1.6
VOUT = 0.9V VOUT = 1.8V VOUT = 2.5V
10
100
1000
1.5 -40
-20
0
20
40
60
80
100
Output Current (mA)
Temperature (C)
Load Regulation
(VOUT = 1.8V; VMODE/SYNC = VIN; L = 2.2H)
1.2
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
6.0 4.0 2.0 0.0
ENABLE and VOUT (Top and Middle) (V)
0.9
ENABLE
Inductor Current (Bottom) (A)
Accuracy (%)
0.6 0.3 0.0 -0.3 -0.6 -0.9 -1.2 0 1 10 100 1000
1.8V
VIN = 4.2V VIN = 3.3V VIN = 3.6V
VOUT IINDUCTOR
0V 1.0 0.5 0.0 -0.5
Output Current (mA)
Time (100s/div)
6
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AAT2503
Adjustable 3-Channel Regulator Typical Characteristics--Step-Down Converter
Turn Off
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
6.0 1.2 4.0 2.0 0.0
Line Regulation
(VOUT = 1.8V; VMODE/SYNC = VIN)
0.9
ENABLE
ENABLE and VOUT (Top and Middle) (V)
Inductor Current (Bottom) (A)
Accuracy (%)
0.6 0.3 0.0 -0.3 -0.6 -0.9 -1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VOUT (1V/div)
1.8V 1.0
IL = 800mA IL = 10mA
IINDUCTOR
0V
0.5 0.0 -0.5
IL = 100mA
Time (100s/div)
Input Voltage (V)
Line Regulation
(VOUT = 0.9V; VMODE/SYNC = VIN)
1.2 0.9
65
No Load Quiescent Current vs. VIN
(VOUT = 1.8V; L = 2.2H)
Quiescent Current (A)
60 55 50 45 40 35 30 25 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Accuracy (%)
0.6 0.3 0.0 -0.3 -0.6 -0.9 -1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
IL = 800mA
TA = 85C
IL = 650mA
TA = 25C TA = -40C
Input Voltage (V)
Input Voltage (V)
No Load Quiescent Current vs. VIN
(VOUT = 0.9V; L = 1H)
50 2.0
Output Voltage Error vs. Temperature
(VIN = 3.6V; VOUT = 0.9V; IOUT = 800mA)
Output Voltage Error (%)
Quiescent Current (A)
45 40 35 30 25 20 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -40
VIN = 1.8V VIN = 2.5V
TA = 85C
TA = 25C TA = -40C
VOUT = 0.9V
-20
0
20
40
60
80
100
Input Voltage (V)
Temperature (C)
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AAT2503
Adjustable 3-Channel Regulator Typical Characteristics--Step-Down Converter
Line Transient
(VOUT = 1.8V; IOUT = 800mA; VIN = 3.6V to 4.2V)
5.0 4.5 4.0 2.5 2.4 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 2.3 2.2 2.0
Load Transient
(VIN = 3.6V; VOUT = 1.8V; IOUT = 300mA to 650mA)
Load and Inductor Current (Bottom) (A)
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
Output Voltage (top) (V)
Input Voltage (top) (V)
1.8 1.6 1.4 1.2 1.0 0.8 0.6
VOUT IOUT
650mA 300mA 0.6
Output Voltage (bottom) (V)
IINDUCTOR
0.3 0.0
Time (20s/div)
Time (20s/div)
Light Load Output Ripple
(VIN = 2.7V; VOUT = 1.8V; IOUT = 1mA)
Heavy Load Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
Output Voltage (AC coupled) (Top) (mV)
Output Voltage (AC coupled) (Top) (mV)
1.4 1.2
20
1.8 1.6
20
VOUT
10 0 -10 -20 -30
Inductor Current (Bottom) (A)
Inductor Current (Bottom) (A)
VOUT
10 0 -10 -20 -30
1.0 0.8 0.6 0.4 0.2 0.0 -0.2
1.4 1.2 1.0 0.8 0.6 0.4 0.2
IINDUCTOR
-40 -50 -60
IINDUCTOR
-40 -50 -60
Time (10s/div)
Time (200ms/div)
8
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AAT2503
Adjustable 3-Channel Regulator Typical Characteristics--LDO Regulator
Dropout Voltage vs. Temperature
(VOUT = 2.8V)
120 100
Dropout Voltage vs. Output Current
(VOUT = 2.8V)
Dropout Voltage (mV)
Dropout Voltage (mV)
100 80 60 40 20 0 -40 -20 0 20 40 60 80
150mA
90 80 70 60 50 40 30 20 10 0 0 20 40 60
85C 25C
100mA 50mA
-40C
100
120
80
100
120
140
160
Temperature (C)
Output Current (mA)
Dropout Characteristics
3.0
DC Regulation
(VIN = 3.6V; VOUT = 1.2V)
2.5 2.0
Output Voltage (V)
DC Regulation (%)
2.9
1mA
2.8 2.7 2.6 2.5 2.4 2.7
10mA
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5
150mA 100mA 50mA
IOUT = 50mA IOUT = 1mA IOUT = 100mA IOUT = 150mA
-40 -20 0 20 40 60 80 100
2.8
2.9
3.0
3.1
3.2
Input Voltage (V)
Temperature (C)
DC Regulation
(VIN = 3.6V; VOUT = 1.8V)
2.5 2.0 2.5 2.0
DC Regulation
(VIN = 3.6V; VOUT = 2.8V)
DC Regulation (%)
DC Regulation (%)
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -40 -20 0 20 40
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5
IOUT = 50mA
IOUT = 1mA
IOUT = 50mA IOUT = 1mA IOUT = 100mA IOUT = 150mA
IOUT = 150mA IOUT = 100mA
60 80 100
-40
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
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AAT2503
Adjustable 3-Channel Regulator Typical Characteristics--LDO Regulator
Quiescent Current vs. Input Voltage
(VOUT = 2.8V)
35
Turn-On Response Time
(VIN = 3.6V; VOUT = 1.8V; IOUT = 150mA)
6 7 6 5 4 3 2 1 0 -1
Quiescent Current (A)
IOUT = 150mA
31
IOUT = 100mA
4 2
Output Voltage (Bottom) (V)
ENABLE (Top ) (V)
5.5
27 23 19 15 2.7
0 -2 -4 -6 -8 -10
IOUT = 50mA IOUT = 10mA
IOUT = 0mA
3.1
3.5
3.9
4.3
4.7
5.1
Input Voltage (V)
Time (10s/div)
Turn-Off Response Time
(VIN = 3.6V; VOUT = 1.8V; IOUT = 150mA)
6 4 2 7 6 2.2 2.0
Load Transient
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA to 100mA)
0.7 0.6
Output Voltage (top) (V)
5 4 3 2 1 0 -1
Output Voltage (Bottom) (V)
Output Current (Bottom) (A)
1.8 1.6 1.4 1.2 1.0 0.8 0.6
0.5 0.4 0.3 0.2 0.1 0.0 -0.1
ENABLE (Top ) (V)
0 -2 -4 -6 -8 -10
Time (50s/div)
Time (200s/div)
Load Transient
(VIN = 3.6V; VOUT = 1.8V; IOUT = 50mA to 100mA)
2.2 2.0 0.7 0.6
Output Current (Bottom) (A)
Output Voltage (Top) (V)
1.8 1.6 1.4 1.2 1.0 0.8 0.6
0.5 0.4 0.3 0.2 0.1 0.0 -0.1
Time (50s/div)
10
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AAT2503
Adjustable 3-Channel Regulator Typical Characteristics--LDO Regulator
Line Transient
(VOUT = 1.8V; IOUT = 100mA; VIN = 3.6V to 4.2V)
5.0 4.5 4.0 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6
5.0 4.5 4.0
Line Transient
(VOUT = 1.8V; IOUT = 150mA; VIN = 3.6V to 4.2V)
2.5
VIN
VIN
2.4 2.3 2.2 2.1 2.0 1.9 1.8
Output Voltage (bottom) (V)
Output Voltage (bottom) (V)
Input Voltage (top) (V)
Input Voltage (top) (V)
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
VOUT
VOUT
1.7 1.6 1.5
Time (100s/div)
Time (100s/div)
Line Regulation
(VOUT = 1.2V)
2.0 1.5
2.0 1.5
Load Regulation
(VOUT = 1.2V)
Output Error (%)
1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 2.7 3.1 3.5 3.9
Output Error (%)
1mA
10mA
1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0 1 10 100 1000
VIN = 2.7V VIN = 3.6V VIN = 5.5V VIN = 4.2V
50mA
150mA 100mA
4.3
4.7
5.1
5.5
Input Voltage (V)
Output Current (mA)
Load Regulation
(VOUT = 2.8V)
2.0 1.5
Output Error (%)
1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0 1 10 100 1000
VIN = 3.3V VIN = 3.6V VIN = 5.5V VIN = 4.2V
Output Current (mA)
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AAT2503
Adjustable 3-Channel Regulator Functional Block Diagram
FB VP VIN
Voltage Reference
Err. Amp.
DH
MODE/SYNC
Control Logic
Logic
DL
LX PGND OUTA
Over-Current Protection
EN VLDOA ENB
Err. Amp.
VLDOB
Err. Amp. Voltage Reference
Over-Current Protection
ENA
94% VREF
FBA POK
OUTB
FBB
AGND
Functional Description
The AAT2503 is a high performance power management IC comprised of a step-down converter and two linear regulators. The step-down converter operates in both fixed and variable frequency modes for high efficiency performance. The switching frequency is 2MHz, minimizing the size of the inductor. The converter requires only three external components (CIN, COUT, and L). The LDOs can deliver up to 150mA each. Each regulator has independent input voltage and enable pins and operates with ceramic capacitors.
operation maintains high efficiency under light load conditions (typically <50mA). The MODE/SYNC pin allows an optional "PWM Only" mode. This maintains constant frequency and low output ripple across all load conditions. Alternatively, the IC can be synchronized to an external clock via the MODE/SYNC input. External synchronization is maintained between 1MHz and 3MHz. It consumes 30A of typical no load quiescent current, making it also ideal for light load applications. The oscillator operates at 2MHz, minimizing the cost and size of external components. A logic low on the EN pin shuts the converter down and makes it consume less than 1A of current. Soft start increases the inductor current limit point in discrete steps when the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot.
Switch-Mode Step-Down Converter
The switching regulator is a monolithic step-down converter operating with input voltage range of 2.7V to 5.5V. Power devices are sized for 800mA current capability and achieve over 95% efficiency. PFM 12
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AAT2503
Adjustable 3-Channel Regulator
For overload conditions, the peak input current is limited. As load impedance decreases and the output voltage falls closer to zero, more power gets internally dissipated, 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 140C with 15C of hysteresis. The step-down converter and the two LDOs have independent enable pins. When pulled low, the enable input forces the LDO into shutdown mode and forces the step-down converter into a lowpower, non-switching state. The input current during shutdown is less than 1A.
Linear Regulators
The two linear regulators are high performance LDOs where each LDO can source up to 150mA of current. For added flexibility, both regulators have independent input voltages operating from 2.8V to 5.5V. An external feedback pin for each LDO allows programming the output voltage from VIN to 0.6V. The regulators have short-circuit and thermal protection in case of adverse operating conditions. LDOA features an integrated Power-OK comparator which indicates when the output is out of regulation. The POK is an open drain output and it is held low when the AAT2503 is in shutdown mode.
Control Loop
The AAT2503 includes a peak current mode stepdown 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 terminates the transconductance voltage error amplifier output. For fixed voltage versions, the error amplifier reference voltage is internally set to program the converter output voltage. For the adjustable output, the error amplifier reference is fixed at 0.9V.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN pin. Under-voltage lockout guarantees sufficient VIN bias and proper operation of all internal circuits prior to activation.
Over-Temperature Protection
Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140C with 15C of hysteresis. Once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers.
Soft Start / Enable
Soft start limits the current surge seen at the input and eliminates output voltage overshoot in the step-down converter.
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AAT2503
Adjustable 3-Channel Regulator Applications Information
Step-Down Converter 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 internal slope compensation for the AAT2503 step-down converter is 0.51A/sec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.5V output and 2.2H inductor. 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.
CIN =
VO V * 1- O VIN VIN
VPP - ESR * FS IO
VO V 1 * 1 - O = for VIN = 2 * VO VIN VIN 4
0.75 VO 0.75 1.5V A m= = = 0.51 L 2.2H sec
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. 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. The 2.2H CDRH2D14 series Sumida inductor has a 94m DCR and a 1.5A DC current rating. At full 800mA load, the inductor DC loss is 17mW which gives a 2.8% loss in efficiency for a 800mA, 1.8V output.
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 10F, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6F. 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.
Input Capacitor
Select a 4.7F to 10F X7R or X5R ceramic capacitor for the input of the step-down converter. To estimate the required input capacitor size, determine
VO V * 1- O = VIN VIN
D * (1 - D) =
0.52 =
1 2
Configuration
0.9V Adjustable With External Feedback
Output Voltage
1V, 1.2V 1.5V, 1.8V 2.5V, 3.3V Table 1: Inductor Values.
Inductor
1.5H 2.2H 3.3H
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2503.2007.04.1.1
AAT2503
Adjustable 3-Channel Regulator
for VIN = 2 x VO:
IO 2
IRMS(MAX) =
VO V * 1- O VIN VIN
cally 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:
3 * ILOAD VDROOP * FS
The term appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT2503. 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. 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. This dampens the high Q network and stabilizes the system.
COUT =
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 4.7F. 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 Output Resistor Selection
The output voltage on the step-down converter is programmed with external resistors R2 and R6. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R6 is 59k. 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. Table 2 summarizes the resistor values for various output voltages with R6 set to either 59k for good noise immunity or 221k for reduced no load input current. With enhanced transient response for extreme pulsed load application, an external feed-forward capacitor (C1 in Fig.3) can be added.
Output Capacitor
The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7F to 10F X5R or X7R ceramic capacitor typi-
2503.2007.04.1.1
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AAT2503
Adjustable 3-Channel Regulator
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 JA for the QFN34-20 package which is 50C/W.
TJ(MAX) = PTOTAL * JA + TAMB
R6 = 59k VOUT (V)
0.9* 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 2.8 3.0 3.3
R6 = 221k R2 (k)
0 24.3 48.7 73.2 97.6 124 147 221 232 274 392 464 511 590
R2 (k)
0 6.65 13.3 19.6 26.1 32.4 39.2 59.0 61.9 71.5 105 124 137 158
LDO Linear Regulator Input Capacitor
A 1F or larger capacitor is typically recommended for CIN in most applications. A CIN capacitor is not required for basic LDO regulator operation; however, if the AAT2503 is physically located more than three centimeters from an input power source, a CIN capacitor will be needed for stable operation. CIN should be located as closely to the device VIN pin as practically possible. CIN values greater than 1F will offer superior input line transient response and will assist in maximizing the highest possible power supply ripple rejection. Ceramic, tantalum, or aluminum electrolytic capacitors may be selected for CIN. There is no specific capacitor ESR requirement for CIN; however, for 150mA LDO regulator output operation, 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.
Table 2: Step-Down Converter Resistor Values for Various Output Voltages.
Thermal Calculations
There are three types of losses associated with the AAT2503 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 LDO losses is given by:
PTOTAL = IO2 * (RDSON(HS) * VO + RDSON(LS) * [VIN - VO]) VIN
Output Capacitor
For proper load voltage regulation and operational stability, a capacitor is required between pins OUTA, OUTB, 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 AAT2503 has been specifically designed to function with very low ESR ceramic capacitors. For best performance, ceramic capacitors are recommended. Typical output capacitor values for maximum output current conditions range from 1F to 10F.
+ (tsw * F * IO + IQ) * VIN
IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load stepdown converter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:
PTOTAL = IO2 * RDSON(HS) + IQ * VIN
* For the 0.9V output, R6 is open.
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2503.2007.04.1.1
AAT2503
Adjustable 3-Channel Regulator
Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteristics of the AAT2503 should use 2.2F or greater for COUT. If desired, COUT may be increased without limit. In low output current applications where output load is less than 10mA, the minimum value for COUT can be as low as 0.47F. temperature; this could cause problems for circuit operation. X7R and X5R dielectrics are much more desirable. The temperature tolerance of X7R dielectric is better than 15%. Capacitor area is another contributor to ESR. Capacitors which are physically large in size will have a lower ESR when compared to a smaller sized capacitor of an equivalent material and capacitance value. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size. Consult capacitor vendor datasheets carefully when selecting capacitors for LDO regulators.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2503. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lower cost, has a smaller PCB footprint, and is non-polarized. Line and load transient response of the LDO regulator is improved by using low ESR ceramic capacitors. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage.
Adjustable Output Resistor Selection
The output voltage on the linear regulator is programmed with external resistors: R4 and R7 for LDOA and R5 and R8 for LDOB. Table 3 summarizes the resistor values for various output voltages with R4 and R5 set to either 59k for good noise immunity or 221k for reduced no load input current. LDO VOUT (V)
0.6* 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.85 2.0 2.5 3.3
Equivalent Series Resistance
ESR is a very important characteristic to consider when selecting a capacitor. ESR is the internal series resistance associated with a capacitor that includes lead resistance, internal connections, size and area, material composition, and ambient temperature. Typically, capacitor ESR is measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors.
R7, R8 = 59k R4, R5 (k)
0 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267
R7, R8 = 221k R4, R5 (k)
0 75 113 150 187 221 261 301 332 442 464 523 715 1000
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1F are typically made from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials. These two material types are not recommended for use with LDO regulators since the capacitor tolerance can vary more than 50% over the operating temperature range of the device. A 2.2F Y5V capacitor could be reduced to 1F over
Table 3: LDO Linear Regulators Resistor Values for Various Output Voltages.
* For the 0.6V output, R7 and R8 are open. 2503.2007.04.1.1
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AAT2503
Adjustable 3-Channel Regulator
POK Output
LDOA of the AAT2503 features an integrated Power OK comparator which can be used as an error flag. The POK open drain output goes low when output voltage is 6% (typ) below its nominal regulation voltage. Additionally, any time LDOA is in shutdown, the POK output is pulled low. Connect a pull-up resistor from POK to OUTA.
No-Load Stability
The LDOs in the AAT2503 are 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.
Reverse Output-to-Input Voltage Conditions and Protection
Under normal operating conditions, a parasitic diode exists between the output and input of the LDO regulator. The input voltage should always remain greater than the output load voltage maintaining a reverse bias on the internal parasitic diode. Conditions where VOUT might exceed VIN should be avoided since this would forward bias the internal parasitic diode and allow excessive current flow into the VOUT pin, possibly damaging the LDO regulator. In applications where there is a possibility of VOUT exceeding VIN for brief amounts of time during normal operation, the use of a larger value CIN capacitor is highly recommended. A larger value of CIN with respect to COUT will effect a slower CIN decay rate during shutdown, thus preventing VOUT from exceeding VIN. In applications where there is a greater danger of VOUT exceeding VIN for extended periods of time, it is recommended to place a Schottky diode across VIN to VOUT (connecting the cathode to VIN and anode to VOUT). The Schottky diode forward voltage should be less than 0.45V.
Enable Function
The AAT2503 features an LDO regulator enable/disable function. Each LDO has its own dedicated enable pin. These pins (ENA, ENB) are active high and are compatible with CMOS logic. To assure the LDO regulators will switch on, ENA/B must be greater than 1.4V. The LDO regulators will shut down when the voltage on the ENA/B pins falls below 0.6V. In shutdown, the LDO regulators will consume less than 1.0A of current. 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.
Short-Circuit Protection
The AAT2503 contains internal short-circuit protection that will trigger when the output load current exceeds the internal threshold limit. Under shortcircuit conditions, the output of the LDO regulator will be current limited until the short-circuit condition is removed from the output or LDO regulator package power dissipation exceeds the device thermal limit.
Thermal Considerations and High Output Current Applications
The LDOs of the AAT2503 are designed to deliver continuous output load currents of 150mA each under normal operation. This is desirable for circuit applications where there might be a brief high inrush current during a power-on event. The limiting characteristic for the maximum output load current safe operating area is essentially package power dissipation and the internal preset thermal limit of the device. In order to obtain high operating currents, careful device layout and circuit operating conditions need to be taken into account.
Thermal Protection
Each of the two LDOs of the AAT2503 has an internal thermal protection circuit which will turn on when the device die temperature exceeds 140C. The LDO regulator outputs will remain in a shutdown state until the internal die temperature falls back below the ~125C trip point. The combination and interaction between the short-circuit and thermal protection systems allows the LDO regulators to withstand indefinite short-circuit conditions without sustaining permanent damage.
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AAT2503
Adjustable 3-Channel Regulator
The following discussions will assume the LDO regulator is mounted on a printed circuit board utilizing the minimum recommended footprint as stated in the layout considerations section of this document. At any given ambient temperature (TA), the maximum package power dissipation can be determined by the following equation: resistance). Typically, maximum conditions are calculated at the maximum operating temperature of TA = 85C and under normal ambient conditions where TA = 25C. Given TA = 85C, the maximum package power dissipation is 800mW. At TA = 25C, the maximum package power dissipation is 2W. The maximum continuous output current for the AAT2503 is a function of the package power dissipation and the input-to-output voltage drop across the LDO regulator. To determine the maximum output current for a given output voltage, refer to the following equation. This calculation accounts for the total power dissipation of the LDO regulator, including that caused by ground current.
PD(MAX) =
TJ(MAX) - TA JA
Constants for the AAT2503 are TJ(MAX) (the maximum junction temperature for the device, which is 125C) and JA = 50C/W (the package thermal
PD(MAX) = [(VIN - VOUTA)IOUTA + (VIN * IGND)] + [(VIN - VOUTB)IOUTB + (VIN * IGND)]
Layout
The suggested PCB layout for the AAT2503 is shown in Figures 2 and 3. The following guidelines should be used to help ensure a proper layout. 1. The input capacitors (C4, C7, C8, and C9) should connect as closely as possible to VIN and PGND. 2. The output capacitor (C5, and C6) of the LDOs connect as closely as possible to OUT. C2 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. Do not make the node small by using a narrow trace. The trace should be kept wide, direct, and short. 3. The feedback trace should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-
current load trace will degrade DC load regulation. Feedback resistors should be placed as closely as possible to VOUT to minimize the length of the high impedance feedback trace. If possible, they should also be placed away from the LX (switching node) and inductor to improve noise immunity. 4. The resistance of the trace from the load return to the 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. Ensure all ground pins are tied to the ground plane. No pins should be left floating. For maximum power dissipation, it is recommended that the exposed Pad must be soldered to a good conductive PCB ground plane layer to further increase local heat dissipation.
2503.2007.04.1.1
19
AAT2503
Adjustable 3-Channel Regulator
Figure 1: AAT2503 Evaluation Board Top Side Layout.
Figure 2: AAT2503 Evaluation Board Bottom Side Layout.
SYNC R10 100k U1
5
AAT2503
LX LX OUTA POK FBA OUTB FBB PGND AGND
9
FB SYNC VIN VINA VINB VP EN/SET ENB ENA
LX L1 VOUT_BUCK
4
8
VIN
R1 100 C4 0.1F
3 2 1
2.2H CDRH2D14
13 17
18 3 2 1
15
R3 100k R4
C2 10F C3 0.01F
R2
C1 100pF
VINA
C8 1F
19
16
VINB
1 2 3
C9 1F
OUTA
10 20
14 1 2 3
1
R5
OUTB
EN
3 1 2 3
7
ENB
2
6
R7 59.0k
R8 59.0k
C6 2.2F
C5 2.2F
R6 59.0k
ENA GND POK
R12 100k
C7 10F
GND GND
GND
C5, C6 2.2F, 10V, X5R, 0603 GRM188R61A225KE34 C8, C9 1F, 6.3V, X5R, 0603 GRM185R60J105KE26 C2, C7 10F, 6.3V, X5R, 0805 GRM219R60J106KE19 L1 Sumida CDRH2D14 or Coltronics SD3814 U1 AAT2503 QFN34-20
Figure 3: AAT2503 Evaluation Board Schematic.
20
2503.2007.04.1.1
AAT2503
Adjustable 3-Channel Regulator
Manufacturer
Murata Murata Murata Murata Murata
Part Number
GRM219R60J106KE19 GRM188R60J475KE19 GRM188R61A225KE34 GRM188R61A105KA61 GRM185R60J105KE26
Value (F)
10 4.7 2.2 1.0 1.0
Voltage Rating
6.3 6.3 10 10 6.3
Temp. Co.
X5R X5R X5R X5R X5R
Case Size
0805 0603 0603 0603 0603
Table 4: Surface Mount Capacitors.
Manufacturer
Sumida Sumida Sumida Coiltronics Coiltronics Coiltronics Taiyo Yuden Taiyo Yuden Taiyo Yuden
Part Number
CDRH2D14-1R5 CDRH2D14-2R2 CDRH2D14-3R3 SD3812-1R5 SD3812-2R2 SD3812-3R3 NR3010-1R5 NR3010-2R2 NR3010-3R3
Inductance (H)
1.5 2.2 3.3 1.5 2.2 3.3 1.5 2.2 3.3
Saturated Rated Current (mA)
1800 1500 1200 1580 1320 1100 1200 1100 870
DCR (m)
63 94 125 78 111 159 80 95 140
Size (mm) LxWxH
3.2x3.2x1.55 3.2x3.2x1.55 3.2x3.2x1.55 4.0x4.0x1.2 4.0x4.0x1.2 4.0x4.0x1.2 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0
Type
Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded
Table 5: Suggested Inductors and Suppliers.
2503.2007.04.1.1
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AAT2503
Adjustable 3-Channel Regulator Ordering Information
Voltage Package
QFN34-20
Channel 1 Channel 2 Channel 3
Marking1
TPXYY
Part Number (Tape and Reel)2
AAT2503IZL-BAA-T1
0.9V
0.6V
0.6V
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
Legend
Voltage Adjustable (0.6V) 0.9 1.2 1.5 1.8 1.9 2.5 2.6 2.7 2.8 2.85 2.9 3.0 3.3 4.2 Code A B E G I Y N O P Q R S T W C
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
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2503.2007.04.1.1
AAT2503
Adjustable 3-Channel Regulator Package Information1
QFN34-20
Detail "A"
Index Area (D/2 x E/2) Detail "B"
7.5 7.5
0.925 0.125
0.025 0.025
0.214 0.036
Side View
3.00 0.05
Top View
4.00 0.05
Bottom View
0.40 0.10 0.075 0.075 Pin 1 indicator (optional)
Option A: C0.30 (4x) max Chamfered corner
Option B: R0.30 (4x) max Round corner
Detail "A" Detail "B"
All dimensions in millimeters.
1. 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.
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737- 4600 Fax (408) 737- 4611
2503.2007.04.1.1
0.50 0.05
0.24 0.06
23

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