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PRODUCT DATASHEET
AAT1130
SwitchRegTM
General Description
The AAT1130 SwitchRegTM is a member of AnalogicTech's Total Power Management ICTM product family. It is a fixed-frequency (during steady-state operation), current-mode step-down converter. The unique architecture improves transient response while allowing tiny passive LC filter components. The high switching frequency (up to 2.5MHz) keeps output voltage ripple low. The AAT1130 delivers up to 500mA of output current, while consuming only 60A of quiescent current. The current-mode control circuit operates at a fixed switching frequency in steady-state operation. It allows the control circuit to react nearly instantly for improved transient response and is stable with LC components as small as 1H and 4.7F. The AAT1130 regulates an output voltage between 0.6V and 1.8V from an input voltage of 2.7V to 5.5V. The AAT1130 is available in either fixed or adjustable output regulation voltage options, for the adjustable version the output voltage is set by an external resistor voltage divider circuit. Internal MOSFET switches reduce the overall solution size while maintaining high efficiency over a wide load current range. The AAT1130 is available in a space saving 2.0x2.2mm SC70JW-10 package, and is rated over the -40C to 85C temperature range.
2.5MHz 500mA Step-Down DC/DC Converter
Features
* * * * * * * * * * * * * * 2.5MHz Switching Frequency Input Voltage Range: 2.7V to 5.5V Output Voltage Range: 0.6V to 1.8V High 92% Peak Efficiency (VIN = 3.6V, VOUT = 1.8V) Low 60A Quiescent Current 500mA Maximum Continuous Output Current Fast Transient Response with Small LC Output Filter Components Fixed and Adjustable Output Voltage Options Internal Soft-Start Anti-Ringing Switch to Reduce EMI During Discontinuous Conduction Mode Operation Over-Temperature Protection Valley Current Limit Protection Available in SC70JW-10 -40C to 85C Temperature Range
Applications
* * * * * * * Microprocessor/DSP Core and I/O Mobile Phones PDAs and Handheld Computers Digital Cameras Portable Music Players Handheld Games Handheld Instruments
Typical Application
L = 1H Input: 2.7V to 5.5V CIN VCC/VP LX Output:1.2V, 500mA max
AAT1130-12 (SC70JW)
VOUT COUT = 4.7F
EN
PGND GND
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Pin Descriptions
Adj.
1 2 3 4 5 6 n/a 7, 8, 9, 10
2.5MHz 500mA Step-Down DC/DC Converter
Fixed
n/a 2 3 4 5 1 6 7, 8, 9, 10
Symbol
FB VOUT VCC VP LX EN PGND GND
Function
Output voltage feedback input. FB senses the output voltage through a resistor voltage divider circuit. Connect the voltage divider from the output voltage to FB. The feedback threshold is 0.6V. (Adjustable output voltage versions only) Output voltage feedback input. VOUT senses the output voltage. Connect VOUT to the output voltage node to regulate the output voltage. Input supply voltage. Connect VCC to the input supply voltage. Power input supply voltage. Connect VP to the VCC pin, and to the input supply voltage. Bypass VP to PGND with a 2.2F or greater capacitor. Switching node. Connect the LC filter between LX and the load. LX is internally connected to the drain of the p-channel MOSFET switch and n-channel MOSFET synchronous rectifier. Enable input. Active logic high. Power ground. Connect PGND to GND at a single point as close to the AAT1130 as possible. Ground. For fixed version, connect GND to PGND at a single point as close to the AAT1130-xx as possible.
Pin Configuration
SC70JW-10 (Top View) Adjustable Output Voltage Version Fixed Output Voltage Version
FB VOUT VCC VP LX
1 2 3 4 5
12 11 10 9 8
GND GND GND GND EN
EN VOUT VCC VP LX
1 2 3 4 5
10 9 8 7 6
GND GND GND GND PGND
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Absolute Maximum Ratings1
Symbol
VVCC, VVP VLX VFB VEN VPGND TJ TLEAD
2.5MHz 500mA Step-Down DC/DC Converter
Description
VCC, VP to GND LX Voltage to PGND FB Voltage to GND EN Voltage to GND PGND Voltage to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
6.0 -0.3 to VVCC\VVP +0.3 -0.3 to VVCC\VVP +0.3 -0.3 to VVCC\VVP +0.3 -0.3 to 0.3 -40 to 150 300
Units
V V V V V C C
Thermal Information
Symbol
PD JA
Description
Maximum Power Dissipation Thermal Resistance2
Value
625 160
Units
mW 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 a FR4 board.
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Electrical Characteristics1
VIN = 3.6V, CIN = COUT = 4.7F, L = 1H. TA = -40C to 85C, unless otherwise noted. Typical values are TA = 25C. Symbol
VIN VOUT VUVLO IQ ISHDN VOUT_TOL (fixed output version) VFB_ACC ILIM RDS(ON)H RDS(ON)L fON tOFF(MIN) ILXLEAK IFBLEAK tS fS TSD THYS VEN(L) VEN(H) IEN
2.5MHz 500mA Step-Down DC/DC Converter
Description
Input Voltage Output Voltage Range UVLO Threshold Quiescent Current Shutdown Current Output Voltage Tolerance Feedback Voltage Accuracy Valley Current Limit High Side Switch On-Resistance Low Side Switch On-Resistance Switch On-Time Minimum Off-Time LX Leakage Current FB Leakage Current Startup Time Switching Frequency Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Enable Pin Current
Conditions
Min
2.7 0.6
Typ
Max
5.5 1.8 2.65
Units
V V V mV A A % V mA ns ns A A s MHz C C
VIN rising Hysteresis Not Switching EN = AGND = PGND VIN = 2.7V to 5.5V, 0 to 500mA Load TA = 25C, No Load -4 0.59 550
100 60
90 1.0 4
VIN = 3.6V, VOUT = 1.2V VIN = 5.5, VLX = 0 to VIN VFB = 5.5V, VEN = 0V, Adj Only From EN Asserted to Output Regulation VOUT = 1.2V, 500mA Load
0.6 650 0.35 0.25 120 75
0.61
1 0.2 150 2.5 140 15 0.6 1.4 -1.0
VIN = VFB =5.5V
1.0
V V A
1. The AAT1130 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.
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Typical Characteristics
Efficiency vs. Load Current
(VOUT = 1V)
100
2
2.5MHz 500mA Step-Down DC/DC Converter
Output Voltage Error vs. Load Current
(VOUT = 1V) Output Voltage Error (%)
1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3 0.0001
90 80
Efficiency (%)
70 60 50 40 30 20 10 0 0.0001 0.001 0.01 0.1
VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
1
0.001
0.01
0.1
1
Load Current (A)
Load Current (A)
Line Regulation
(VOUT = 1V)
1 100
Efficiency vs. Load Current
(VOUT = 1.8V)
IOUT = 1mA IOUT = 10mA IOUT = 100mA IOUT = 300mA IOUT = 500mA
90 80
Output Voltage Error (%)
0.75 0.5 0.25 0 -0.25 -0.5 -0.75 -1 2.7 3.2 3.7 4.2 4.7
Efficiency (%)
70 60 50 40 30 20 10
VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
0.001 0.01 0.1 1
5.2
5.7
0 0.0001
Input Voltage (V)
Load Current (A)
Output Voltage Error vs. Load Current
(VOUT = 1.8V) Output Voltage Difference (%)
1 1 0.75 0.5 0.25 0 -0.25 -0.5 -0.75 -1 2.7 3.2
Line Regulation
(VOUT = 1.8V)
IOUT = 1mA IOUT = 10mA IOUT = 100mA IOUT = 300mA
Output Voltage Error (%)
0.5 0 -0.5 -1 -1.5 -2 -2.5 -3 0.0001
VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
0.001 0.01 0.1 1
3.7
4.2
4.7
5.2
5.7
Load Current (A)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Typical Characteristics
Supply Current vs. Supply Voltage (Switching)
Switching Frequency (MHz)
100 4 3.75 3.5 3.25 3 2.75 2.5 2.25 2 2.7
2.5MHz 500mA Step-Down DC/DC Converter
Switching Frequency vs. Input Voltage
(VOUT = 1V; CIN = COUT = 2.2F; L = 1H)
Supply Current (A)
95 90 85 80 75 70 65 60 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Supply Voltage (V))
Input Voltage (V)
On-Time vs. Input Voltage
(VOUT = 1V; CIN = COUT = 2.2F; L = 1H)) Switching Frequency (MHz)
250 3 2.75 2.5 2.25 2 1.75 1.5 1.25
Switching Frequency vs. Input Voltage
(VOUT = 1.8V; CIN = COUT = 2.2F; L = 1.5H))
200
On-Time (ns)
150
100
50
0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
1 2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
On-Time vs. Input Voltage
Switching Frequency Variation (%) (VOUT = 1.8V; CIN = COUT = 2.2F; L = 1.5H))
400 350 20 15 10 5 0 -5 -10 -15 -20 200
Switching Frequency Variation vs. Load Current
VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
On-Time (ns)
300 250 200 150 100 50 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
250
300
350
400
450
500
550
600
Input Voltage (V)
Load Current (mA)
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Typical Characteristics
Supply Current vs. Temperature
100 0.2
2.5MHz 500mA Step-Down DC/DC Converter
Output Voltage Error vs. Temperature
Output Voltage Error (%)
Supply Current (A)
90 80 70 60 50 40 30 20 -40 -15 10 35 60 85
0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 -40 -15 10 35 60 85
Temperature (V)
Temperature (C)
RDS(ON) vs. Temperature
450 400 100 90 80
Efficiency vs. Load Current
(VOUT = 1.8V Fixed)
Efficiency (%)
350
RDS(ON) (m)
300 250 200 150 100 50 0 -40 -15 10 35 60 85
70 60 50 40 30 20
PMOS NMOS
10 0 0.0001 0.001 0.01 0.1
VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
1
Temperature (C)
Load Current (A)
Output Voltage Error vs. Load Current
(VOUT = 1.8V Fixed)
2 1
Line Regulation
(VOUT = 1.8V Fixed) Output Voltage Error (%)
IOUT = 1mA IOUT = 10mA IOUT = 100mA IOUT = 300mA
Output Voltage Error (%)
1.5 1 0.5 0 -0.5 -1 -1.5 -2 0.0001
VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5V VIN = 5.5V
0.75 0.5 0.25 0 -0.25 -0.5 -0.75 -1 2.7 3.2 3.7 4.2 4.7
0.001
0.01
0.1
1
5.2
5.7
Load Current (A)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Typical Characteristics
Switching Frequency vs. Output Voltage
(IOUT = 500mA) Switching Frequency (MHz)
3.75 1.90
2.5MHz 500mA Step-Down DC/DC Converter
Load Transient
(VOUT = 1.8V Fixed; VIN = 3.6V; COUT = 4.7F; L = 1.5H)
1.6 1.4 1.2 1.0 0.8 500mA 0.6 0.4 10mA 0.2 0
Output Voltage (top) (V)
1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50
3.25
Output Current (bottom) (A)
2.75
2.25
1.75
1.25 0.6
0.9
1.2
1.5
1.8
Output Voltage (V)
Time (5s/div)
Load Transient
(VOUT = 1.8V Fixed; VIN = 3.6V; COUT = 4.7F; L = 1.5H)
1.90 0.8 1.90
Load Transient
(VOUT = 1.8V; VIN = 3.6V; COUT = 4.7F; CFF = 100pF; L = 1.5H)
0.8 0.7 0.6 0.5 0.4 300mA 1.65 1.60 1.55 1.55 100mA 0.1 0.0 0.3 0.2
Output Voltage (top) (V)
Output Voltage (top) (V)
1.85 1.80 1.75 1.70 300mA 1.65 1.60 100mA 1.55 1.50
0.7
1.85 1.80 1.75 1.70
Output Current (bottom) (A)
Output Current (bottom) (A)
0.6 0.5 0.4 0.3 0.2 0.1 0.0
Time (5s/div)
Time (5s/div)
Load Transient
(VOUT = 1.8V; VIN = 3.6V; COUT = 4.7F; L = 1.5H)
1.90 0.8 0.7 0.6 0.5 0.4 300mA 1.65 1.60 100mA 1.55 1.50 0.1 0 0.3 0.2 1.90
Load Transient
(VOUT = 1.8V; VIN = 3.6V; COUT = 4.7F; CFF = 100pF; L = 1.5H)
1.6 1.4 1.2 1.0 0.8 500mA 0.6 0.4 10mA 0.2 0
Output Voltage (top) (V)
1.85 1.80 1.75 1.70
Output Voltage (top) (V)
1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50
Output Current (bottom) (A)
Output Current (bottom) (A)
Time (5s/div)
Time (5s/div)
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Typical Characteristics
Load Transient
(VOUT = 1.8V; VIN = 3.6V; COUT = 4.7F; L = 1.5H)
1.90 1.6 1.60
2.5MHz 500mA Step-Down DC/DC Converter
Load Transient
(VOUT = 1.5V; VIN = 3.6V; COUT = 4.7F; CFF = 100pF; L = 1.5H)
1.6 1.4
Output Voltage (top) (V)
Output Voltage (top) (V)
1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50 10mA 500mA
1.4
1.55 1.50 1.45 1.40 1.35 1.30 1.25 1.20 10mA 500mA
Output Current (bottom) (A)
Output Current (bottom) (A)
1.2 1.0 0.8 0.6 0.4 0.2 0
1.2 1.0 0.8 0.6 0.4 0.2 0
Time (5s/div)
Time (5s/div)
Load Transient
(VOUT = 1.5V; VIN = 3.6V; COUT = 4.7F; L = 1.5H)
1.60 1.6 1.4 1.2 1.0 0.8 500mA 0.6 0.4 10mA 0.2 0 1.60
Load Transient
(VOUT = 1.5V; VIN = 3.6V; COUT = 4.7F; CFF = 100pF; L = 1.5H)
0.8 0.7 0.6 0.5 300mA 0.4 0.3 100mA 0.2 0.1 0
Output Voltage (top) (V)
1.55 1.50 1.45 1.40 1.35 1.30 1.25 1.20
Output Voltage (top) (V)
1.55 1.50 1.45 1.40 1.35 1.30 1.25 1.20
Output Current (bottom) (A)
Output Current (bottom) (A)
Time (5s/div)
Time (5s/div)
Load Transient
(VOUT = 1.5V; VIN = 3.6V; COUT = 4.7F; L = 1.5H)
1.60 0.8 1.10
Load Transient
(VOUT = 1V; VIN = 3.6V; COUT = 4.7F; CFF = 100pF; L = 1H)
1.6 1.4 1.2 1.0 0.8 0.6 400mA 100mA 0.4 0.2 0
Output Voltage (top) (V)
Output Voltage (top) (V)
1.55 1.50 1.45 1.40 300mA 1.35 1.30 100mA 1.25 1.20
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.70
Output Current (bottom) (A)
Output Current (bottom) (A)
Time (5s/div)
Time (5s/div)
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Typical Characteristics
Load Transient
(VOUT = 1V; VIN = 3.6V; COUT = 4.7F; L = 1H)
1.10 1.6 1.10
2.5MHz 500mA Step-Down DC/DC Converter
Load Transient
(VOUT = 1V; VIN = 3.6V; COUT = 4.7F; CFF = 100pF; L = 1H)
1.6 1.4 1.2 1.0 0.8 500mA 0.6 0.4 10mA 0.2 0
Output Voltage (top) (V)
Output Voltage (top) (V)
1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.70 400mA 100mA
1.4
1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.70
Output Current (bottom) (A)
Output Current (bottom) (A)
1.2 1.0 0.8 0.6 0.4 0.2 0
Time (5s/div)
Time (5s/div)
Load Transient
(VOUT = 1V; VIN = 3.6V; COUT = 4.7F; L = 1H)
1.10 1.6 1.4 1.2 1.0 0.8 500mA 0.6 0.4 10mA 0.2 0
Soft-Start
(VOUT = 1.8V Fixed; VIN = 3.6V; COUT = 4.7F; L = 1.5H) Enable Voltage (top) (V) Output Voltage (middle) (V)
(2V/Div) 0V
Output Voltage (top) (V)
1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.70
3.6V
Output Current (bottom) (A)
Output Current (bottom) (A)
1.8V (1V/Div) 0V 200mA (100mA/Div) 0mA
Time (5s/div)
Time (100s/div)
Line Transient
(VOUT = 1.8V Fixed; COUT = 4.7F; L = 1.5H)
1.90 6.6 6.1
Output Voltage (top) (V)
1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50
Output Voltage (bottom) (V)
5.6 5.1 4.6 4.1 3.6 3.1 2.6
Time (10s/div)
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Functional Block Diagram
VP
2.5MHz 500mA Step-Down DC/DC Converter
VCC
Control and FET Driver Logic Circuitry Shoot Through Protection Current Limit Comparator
LX
VILIM
Error Comparator
Current Sense Amplifier
PGND [Fixed Only] VOUT FB [Adj Only]
EN
Soft-Start
+ -
VREF
GND
Functional Description
The AAT1130 is a high performance 500mA 2.5MHz (maximum switching frequency during steady-state operation) monolithic step-down converter. It minimizes external component size, enabling the use of a tiny 0603 inductor that is only 1mm tall, and optimizes efficiency over the complete load range. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. Typically, a 1H inductor and a 4.7F ceramic capacitor are recommended for <1.2V output voltage applications (see table of values). Only three external power components (CIN, COUT, and L) are required, for fixed output voltage options. Output voltage is programmed with external feedback resistors, ranging from 0.6V to 1.8V. An additional feed-forward capacitor can also be added to the external feedback to provide improved transient response (see Figure 1). The input voltage range is 2.7V to 5.5V. The converter efficiency has been optimized for all load conditions, ranging from no load to 500mA. The internal error comparator and incorporated compensation provide excellent transient response, load, and line
regulation. Soft-start eliminates any output voltage overshoot when the enable or the input voltage is applied.
Control Loop
The AAT1130 uses a current-mode control scheme that allows it to operate at very high switching frequencies. The current-mode control scheme operates with a fixed on-time for a given input voltage. The on-time varies inversely proportional to the input voltage and proportional to the output voltage giving the regulator a fixed switching frequency when in steady-state. This allows the use of very small external inductor and capacitor. The small size coupled with the low quiescent current and automatic transition to variable switching frequency mode makes it ideal for small battery operated applications.
Light Load Operation
The AAT1130 monitors the synchronous rectifier current and when the current drops to zero, it turns off the synchronous rectifier to emulate an actual rectifier. This allows the regulator to operate in discontinuous conduc-
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
tion mode. In this mode the on-time remains the same as it is in continuous conduction mode, and therefore the inductor ripple current remains the same in both modes. But reduced load current requires more time for the output capacitor to discharge to the regulation voltage reducing the switching frequency. This has the added benefit of reducing the switching transition losses improving efficiency at light loads.
2.5MHz 500mA Step-Down DC/DC Converter
Example: Given that VOUT = 1.2V, then COUT > 4.24F, therefore a 4.7F capacitor is suitable. Due to the unique control method, the "inside" current control loop does not have the inherent instability that plagues most fixed frequency current-mode DC-DC regulators.
Stability
The AAT1130 requires no additional compensation components to guarantee stability. The only requirement for stability is to choose the appropriate output capacitor. Current-mode control simplifies compensation by controlling the inductor current to regulate the output voltage. This approximates a single pole response in the loop gain even though a complex pole pair exists due to the LC filter. Therefore the crossover frequency is approximated as the DC loop gain multiplied by the single pole. The AAT1130 DC loop gain is a function of the 60m current sense resistor and is determined by the equation:
Soft-Start
When the AAT1130 is enabled, it enters soft-start mode. In this mode, the output voltage slowly rises over 150s allowing the output capacitor to charge without drawing excessive input current. This feature prevents overstressing the battery or other input power source.
Current Limit
The AAT1130 includes a cycle-by-cycle current limit to prevent damage to itself and external circuitry. The current limit is a valley current limit using the n-channel synchronous rectifier to measure the current. If the synchronous rectifier current is above the valley current limit, the AAT1130 holds the synchronous rectifier on until the current is below the limit. This allows the AAT1130 to control the current in current limit even with a hard shorted output.
VOUT RLOAD ALOOP(DC) = 0.6V * 60m
And the dominant pole frequency is:
fP =
1 2 * RLOAD * COUT
Anti-Ringing Switch
The AAT1130 includes an anti-ringing switch that dissipates any energy left in the inductor when the current is approximately zero. The anti-ringing switch turns on when both the p-channel switch and n-channel synchronous rectifier are off and the inductor current is approximately zero. The switch shorts the LX and VOUT nodes together, effectively shorting the inductor. The low onresistance of the anti-ringing switch dissipates any energy left in the inductor preventing ringing at light loads. When either the switch or synchronous rectifier are on, the anti-ringing switch remains off.
Therefore the crossover frequency is:
fC = ALOOP(DC) * fP = VOUT 2 * 0.6V * 60m * COUT
The only requirement for stability is that the crossover frequency be much less than the 2.5MHz switching frequency. The crossover frequency can be as high as 1/2 of the switching frequency, or 1.25MHz. Therefore calculate the output capacitor by the equation:
Over-Temperature
The AAT1130 includes thermal protection that automatically turns off the regulator when the die temperature exceeds a safe level. The thermal protection turns on at a die temperature of 140C and has a 15C hysteresis.
COUT >
VOUT 2 * 0.6V * 60m * 1.25MHz
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Applications Information
Inductor Selection
The step-down converter uses valley 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. Table 1 displays suggested inductor values for various output voltages. 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. See Table 3 for suggested inductor values and vendors. Output Voltage
1V, 1.2V, 1.3V 1.5V, 1.8V
2.5MHz 500mA Step-Down DC/DC Converter
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.
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 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 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.
Configuration
Adjustable and Fixed Output Voltage
Inductor Value
1.0H to 1.5H 1.5H to 2.2H
Table 1: Inductor Values for Specific Output Voltages.
Input Capacitor
Select a 4.7F to 10F X7R or X5R ceramic capacitor for the input. 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 input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1130. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C1) can be seen in the evaluation board layouts in Figures 4, 5, 6, and 7.
CFF
FB
R1
R2
Figure 1: AAT1130 External Resistor Output Voltage Programming.
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Feedback Resistor Selection
Resistors R1 and R2 of Figure 4 program the output to regulate at a voltage higher than 0.6V. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R2 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 R2 set to either 59k for good noise immunity or 221k for reduced no load input current.
2.5MHz 500mA Step-Down DC/DC Converter
IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down 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 * RDS(ON)H + IQ * VIN
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 SC70JW-10 package which is 160C/W.
R1 =
1.5V VOUT VFB -1 * R2 = 0.6V - 1 * 59k = 88.5k
The AAT1130, combined with an external feedforward capacitor (C3 in Figure 4), delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger output capacitor C1 for stability. R2 = 59k R1 (k)
29.4 39.2 49.9 59.0 68.1 78.7 88.7 118
TJ(MAX) = PTOTAL * JA + TAMB
Layout
The suggested PCB layout for the AAT1130 is shown in Figures 1, 2, and 3. The following guidelines should be used to help ensure a proper layout: 1. The input capacitor (C1) should connect as closely as possible to VCC/VP (pins 3 and 4) and PGND/GND (pins 7-10 for adjustable output voltage and pins 6-10 for fixed output voltage). C1 and L1 should be connected as closely as possible. The connection of L1 to the LX (pin 5) should be as short as possible. The feedback trace or FB (pin 1 for adjustable output voltage) 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. If external feedback resistors are used, they should be placed as closely as possible to the FB (pin 1 for adjustable output voltage) to minimize the length of the high impedance feedback trace. The resistance of the trace from the load return to the PGND/GND (pins 7-10 for adjustable output voltage and pins 6-10 for fixed output voltage) 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.
VOUT (V)
0.9 1 1.1 1.2 1.3 1.4 1.5 1.8
R2 = 221k R1 (k)
113 150 187 221 261 301 332 442
2.
3.
Table 2: Feedback Resistor Values.
Thermal Calculations
There are three types of losses associated with the AAT1130 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the losses is given by:
4.
PTOTAL =
IO2 * (RDS(ON)H * VO + RDS(ON)L * [VIN - VO]) VIN
+ (tsw * FS * IO + IQ) * VIN
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
J1 HEADER
3
2.5MHz 500mA Step-Down DC/DC Converter
C A
1
B
2
U1
1
VOUT VIN
2 3 4
EN VOUT VCC VP LX
GND GND GND GND PGND
10 9 8 7 6
GND
C1 4.7F L1
5
AAT1130 _ FIXED
VOUT C2 4.7F VOUT 1.2V 1.8V L1 1.2H, 1.5H 1.5H, 2.2H
Figure 2: AAT1130 Fixed Output Voltage Evaluation Board Schematic.
R2 59k R1 C3 100pF U1
1 2 3 4
GND GND GND GND GND EN
10 9 8 7 1 6 2
FB VOUT VCC VP LX
VIN
VOUT
VIN
GND
C1 4.7F L1
5
B
A
C
3
AAT1130_ ADJ VOUT 1V 1.3V, 1.5V 1.8V L1 1H 1.5H 1.5H, 2.2H J1 HEADER
VOUT C2 4.7F
Figure 3: AAT1130 Adjustable Output Voltage Evaluation Board Schematic.
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PRODUCT DATASHEET
AAT1130
SwitchRegTM 2.5MHz 500mA Step-Down DC/DC Converter
Figure 4: AAT1130 Fixed Output Voltage Evaluation Board Top Side PCB Layout.
Figure 5: AAT1130 Fixed Output Voltage Evaluation Board Bottom Side PCB Layout.
Figure 6: AAT1130 Adjustable Output Voltage Evaluation Board Top Side PCB Layout.
Figure 7: AAT1130 Adjustable Output Voltage Evaluation Board Bottom Side PCB Layout.
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Manufacturer Part Number/Type
LQM2HP_G0 Murata LQH32P_N0 GLC2518 TDK VLF3010A VLF3010S
2.5MHz 500mA Step-Down DC/DC Converter
Inductance (H)
1 1.5 2.2 1 1.5 2.2 1 2.2 1.5 2.2 1 2.2
Rated Current (mA)
1600 1500 1300 2050 1750 1600 2.8 2.45 1200 1000 1700 1100
DCR (m) (typ)
55 70 80 45 57 76 20 25 68 100 41 77
Size (mm) LxWxH
2.5x2x1
3.2x2.5x1.6 2.5x1.8x1.8 2.8x2.6x1 3.0x2.8x1
Table 3: Suggested Inductor Components. Manufacturer
AVX TDK
Part Number
0603ZD225K C1608X5R1C225K C1608X5R1A475K C2012X5R1A106K C3216X5R1A226K GRM188R61A225K GRM219R61A106K GRM31CR71A226K LMK107BJ475KA
Value
2.2F 2.2F 4.7F 10F 22F 2.2F 10F 22F 4.7F
Voltage
10 16 10 10 10 10 10 10 10
Temp. Co.
X5R X5R
Case
0603 0603 0805 1206 0603 0805 1206 0603
Murata Taiyo Yuden
X5R X7R X5R
Table 4: Suggested Capacitor Components.
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Ordering Information
Output Voltage
Adjustable 1.8V
2.5MHz 500mA Step-Down DC/DC Converter
Package
SC70JW-10 SC70JW-10
Marking1
2VXXY 2UXXY
Part Number (Tape and Reel)2
AAT1130IJQ-0.6 AAT1130IJQ-1.8
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/about/quality.aspx.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
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PRODUCT DATASHEET
AAT1130
SwitchRegTM
Package Information
SC70JW-10
0.40 BSC
2.5MHz 500mA Step-Down DC/DC Converter
1.75 0.10 0.225 0.075
Top View
2.00 0.20 0.15 0.05
0.85 0.15
2.20 0.20 1.10 MAX
0.100
0.45 0.10 2.10 0.30
4 4
7 3
Side View
All dimensions in millimeters.
End View
Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611
(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.
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