ANALOGICTECH AAT2689

PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
General Description
Features
The AAT2689 provides two independently regulated DC
outputs, consisting of a high voltage step-down (Buck)
regulator and a low input voltage low dropout (LDO) regulator. The PMIC is optimized for low cost 12V adapter
inputs, making the device the ideal system-on-a-chip
power solution for consumer communications equipment.
• 2-Output Step-Down Converters:
▪ Channel 1 (Buck): VIN1 = 6V to 24V
• VOUT1 adjustable from 1.5V to 5.5V
• IOUT1 up to 2.5A
• High Switching Frequency
• Voltage Mode Control
• PWM Fixed Frequency for Low-Ripple
▪ Channel 2 (LDO): VIN2 = 2.7V to 5.5V
• IOUT2 up to 600mA
• 1V Dropout Voltage at 600mA
• High Accuracy ±1.5%
• Small Solution Size
▪ System on a Chip
▪ Ultra-small External L/C
• Shutdown Current <35μA
• Independent Enable Pins
• Adjustable Over-Current Protection
• Over-Temperature Protection
• Internal Soft Start
• 3x4mm 16-Pin TDFN Low Profile Thermally Enhanced
Package
• -40°C to 85°C Temperature Range
Channel 1 is a step-down (Buck) regulator with an input
voltage range of 6V to 24V providing up to 2500mA output current. 490kHz fixed switching frequency allows
small L/C filtering components. Channel 1 utilizes voltage mode control configured for optimum performance
across the entire output voltage and load range.
Channel 2 is a low-dropout (LDO) regulator providing up
to 600mA output current. The device provides extremely
low output noise, low quiescent current and excellent
transient response.
The controller includes integrated cycle-by-cycle overcurrent protection, soft-start and over-temperature disable features. Independent input and enable pins provide maximum design flexibility.
The AAT2689 is available in the Pb-free 3x4mm 16-pin
TDFN package. The rated operating temperature range is
-40°C to 85°C.
Applications
•
•
•
•
DSL and Cable Modems
Notebook Computers
Satellite Settop Box
Wireless LAN Systems
Typical Application
C4
0.1µF
TDFN34-16
LX1
BST1
D1
VIN1
6.0V -24.0V
C6
2.2µF
1
VL1
IN1
D2
RS1
R2
2k
C7
220nF
C15
1µF
25V
EN1
FB1
VIN2
C5
2.2µF
IN2
COMP1
EN2
OUT2
GND
2689.2008.06.1.0
R3
27.4k
C9,C11
2x22µF
AAT2689
EN1
+
C8
330pF
R5
499
OS1
C1
220µF
25V
VOUT1
3.3V/2.5A
L1 4.7µH/5.3A
R1 24.3K
C2 470pF
C3 56pF
C10
2.2µF
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VOUT2
1.8V/600mA
R4
6.04k
1
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Pin Descriptions
Pin #
Symbol
1
IN1
2
BST1
3
EN1
4
RS1
5
OS1
6
COMP1
7
FB1
8
EN2
9
IN2
10
OUT2
11
AGND
12
VL1
13
GND
14
IN1
15
LX1
16
LX1
EP1
GND
EP2
IN1
Function
Input supply voltage pin for Channel 1 step-down (Buck) regulator. Connect both IN1 pins together. Connect
the input capacitor close to this pin for best noise performance.
Channel 1 step-down (Buck) regulator boost drive input pin. Connect the cathode of fast rectifier from this pin
and connect a 100nF capacitor from this pin to the Channel 1 switching node (LX) for internal hi-side MOSFET
gate drive.
Channel 1 step-down (Buck) regulator enable input pin. Active high enables internal linear regulator and
Channel 1 output.
Channel 1 output current sense pin. Connect a small signal resistor from this pin to the Channel 1 switching
node (LX) to enable over-current sense for step-down (Buck) converter.
Channel 1 output sense voltage pin. Connect to the output capacitor to enable over-current sense for stepdown (Buck) converter.
Compensation pin for Channel 1 step-down (Buck) regulator. Connect a series resistor and capacitor network
to compensate for the voltage mode control loop.
Feedback input pin for Channel 1 step-down (Buck) converter. Connect an external resistor divider to this pin
to program the output voltage to the desired value.
Channel 2 linear low dropout (LDO) enable input pin. Active high.
Input supply voltage pin for Channel 2 linear low dropout (LDO) regulator. Connect a 2.2μF ceramic input
capacitor close to this pin.
Output of Channel 2 of linear low dropout (LDO) regulator. Connect a 2.2μF ceramic capacitor from this pin to
the GND pin.
Analog ground pin for LDO and Buck (step-down) controller. Tie to PCB ground plane.
Internal linear regulator for Channel 1 step-down (Buck) converter. Connect a 2.2μF/6.3V capacitor from this
pin to the GND pin.
Ground pin for both channels. Power return pin for both channels. Connect returns of both channels input and
output capacitors close to this pin for best noise performance.
Input supply voltage pin for Channel 1 step-down (Buck) regulator. Connect both IN1 pins together. Connect
the input capacitor close to this pin for best noise performance.
Channel 1 step-down (Buck) converter switching pin. Connect output inductor to this pin. Connect both LX1
pins together.
Channel 1 step-down (Buck) converter switching pin. Connect output inductor to this pin. Connect both LX1
pins together.
Exposed paddle 1 tied to ground. Connect to PCB heatsink for optimum thermal performance of internal LDO
device.
Exposed paddle 2 tied to drain of internal high side MOSFET. Connect to PCB heatsink for optimum thermal
performance of step-down (Buck) regulator.
Pin Configuration
TDFN34-16 Dual Paddle
(Top View)
IN1
BST1
EN1
RS1
OS1
COMP1
FB1
EN2
2
1
2
EP2
16
15
3
14
4
13
5
6
12
EP1
11
7
10
8
9
LX1
LX1
IN1
GND
VL1
AGND
OUT2
IN2
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2689.2008.06.1.0
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Absolute Maximum Ratings1
Symbol
Description
VIN(HI), VEN1
VIN(LO)
VBST1-LX1
VCONTROL
VEN2
IIN(PULSED)
TJ
TLEAD
IN1, LX, EN1 to GND
IN2, VL1 to GND
BST1 to LX1
FB1, COMP1, RS1, OS1, OUT2 to GND
EN2 to GND
IN to LX
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 30.0
-0.3 to 6.0
-0.3 to 6.0
-0.3 to VIN(LO) + 0.3
-0.3 to VIN2 + 0.3
12.0
-40 to 150
300
V
V
V
V
V
A
°C
°C
Value
Units
50
2.0
°C/W
W
Thermal Information
Symbol
ΘJA
PD
Description
Thermal Resistance2
Maximum Power Dissipation3
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board with exposed paddle connected to ground plane.
3. Derate 20mW/°C above 25°C ambient temperature.
2689.2008.06.1.0
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3
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Electrical Characteristics1
VIN1 = 12.0V, VIN2 =3.3V; TA = -40°C to 85°C, unless noted otherwise. Typical values are at TA = 25°C.
Symbol
Description
Conditions
Channel 1: Step-Down (Buck) Converter
VIN1
Input Voltage
VUVLO1
UVLO Threshold
Min
Typ
6.0
VIN1 Rising
VIN1 Hysteresis
VIN1 Falling
Output Voltage Range
VOUT1
VFB1
Feedback Pin Voltage
VOUT1
Output Voltage Accuracy
IOUT1 = 0 to 2.5A
(ΔVOUT1/VOUT1) /
VIN1 = 6V to 24V, VOUT1 = 3.3V,
Line Regulation
ΔVIN1
IOUT1 = 0V to 2.5A
(ΔVOUT1/VOUT1) /
VIN1 = 6V to 24V, VOUT1 = 3.3V,
Load Regulation
ΔIOUT1
IOUT1 = 0A to 2.5A
IQ1
Quiescent Current
VEN1 = High, No load
Shutdown Current
VEN1 = Low, VL1 = 0V
ISHDN1
VOCP1
Over-Current Offset Voltage
VEN1 = High, VIN1 = 6V to 24V, TA = 25°C
ILX1
LX Pin Leakage Current
VIN1 = 24.0V, VEN1 = Low
DMAX
Maximum Duty Cycle
TON(MIN)
Minimum On-Time
VIN1 = 6V to 24V
RDSON(H)
Hi Side On-Resistance
VL1 = 4.5V
FOSC1
Oscillator Frequency
FFOLDBACK1
Short Circuit Foldback Frequency Current Limit Triggered
TS1
Start-Up Time
From Enable Channel 1 to Output Regulation
Channel 2: 600mA Linear Low Dropout (LDO) Regulator
VIN2
Input Voltage
VDO2
Dropout Voltage
98% x VOUT2(NOM), IOUT2 = 600mA
IQ2
Quiescent (Ground) Current
No load
ISHDN2
Shutdown Current
VEN2 = GND
IOUT2 = 1 to 600mA, VIN2 = 2.7V to 5.5V,
TA = 25°C
VOUT2(TOL)
Output Voltage Tolerance
IOUT2 = 1 to 600mA, VIN2 = 2.7V to 5.5V,
TA = -40°C to 85°C
Output Noise
BW = 300Hz to 50kHz
eN
1kHz
PSRR
Power Supply Rejection Ratio
IOUT2 = 10mA
10kHz
1MHz
ILIMIT2
Current Limit
TS2
Enable Start-Up Delay
From Enable Channel 2 to Output Regulation
Over-Temperature, EN Logic
Over-Temperature Shutdown
Threshold
TSD1,2
Over-Temperature Shutdown
Hysteresis
VEN1,EN2(L)
Enable Threshold Low
Enable Threshold High
VEN1(H)
VEN2(H)
Enable Threshold High
IEN1,EN2
Input Low Current
Max
Units
24.0
5.0
V
V
mV
V
V
V
%
300
3.0
1.5
0.591
-3.0
0.600
5.5
0.609
+3.0
0.014
%/V
0.1
%/A
0.6
80
-1.0
350
100
85
100
70
490
100
2.5
2.7
35.0
120
1.0
650
mA
μA
mV
μA
%
ns
mΩ
kHz
kHz
ms
5.5
1300
125
1.0
V
mV
μA
μA
-2.0
+2.0
%
-3.5
+3.5
%
1000
70
700
250
67
47
45
800
15
μVRMS
135
°C
15
°C
dB
mA
μs
0.6
2.5
1.4
-1.0
1.0
V
V
V
μA
1. The AAT2689 is guaranteed to meet performance specifications over the –40°C to +85°C operating temperature range and is assured by design, characterization and correlation with statistical process controls.
4
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2689.2008.06.1.0
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics
Step-Down Converter Efficiency vs. Load
Step-Down Converter DC Regulation
(VOUT1 = 3.3V; L = 4.7µH)
(VOUT1 = 3.3V; L = 4.7µH)
2.0
90
1.5
Efficiency (%)
80
70
60
50
40
VIN1 = 6V
VIN1 = 8V
VIN1 = 12V
VIN1 = 18V
VIN1 = 24V
30
20
10
0
0.1
1
10
100
1000
10000
Output Error (%)
100
1.0
0.5
0.0
VIN1 = 6V
VIN1 = 8V
VIN1 = 12V
VIN1 = 18V
VIN1 = 24V
-0.5
-1.0
-1.5
-2.0
0.1
1
10
Output Current (mA)
Step-Down Converter Output Ripple
(VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 1mA)
Output Voltage (AC coupled)
(bottom) (V)
0.50
0.25
0.00
-0.25
IOUT1 = 0.1mA
IOUT1 = 1mA
IOUT1 = 1250mA
IOUT1 = 2500mA
-0.50
-0.75
6
8
10
12
14
16
18
20
22
12V
0V
0.4
0.2
0.0
3.31
3.30
3.29
LX Voltage (top) (V)
Inductor Current (middle) (A)
Accuracy (%)
10000
(VOUT1 = 3.3V; L = 4.7µH)
0.75
24
Input Voltage (V)
Time (2µs/div)
Step-Down Converter Load Transient Response
(VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 2.5A)
(IOUT1 = 1.875A to 2.5A; VIN1 = 12V;
VOUT1 = 3.3V; COUT1 = 2x22µF)
12V
4.0
3.0
2.0
3.32
3.30
3.28
Time (1µs/div)
2689.2008.06.1.0
2.5A
3.0
2.5
2.0
1.875A
1.5
3.4
3.3
Output Current
(top) (A)
0V
Output Voltage
(AC Coupled) (bottom) (V)
Step-Down Converter Output Ripple
LX Voltage (top) (V)
Inductor Current (middle) (A)
Output Voltage (AC coupled)
(bottom) (V)
1000
Step-Down Converter Line Regulation
1.00
-1.00
100
Output Current (mA)
3.2
Time (100µs/div)
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PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics
Step-Down Converter Line Transient Response
(IOUT1 = 1.25A to 2.5A; VIN1 = 12V;
VOUT1 = 3.3V; COUT1 = 2x22µF)
(VIN1 = 6V to 10V; VOUT1 = 3.3V; IOUT1 = 2.5A)
3.0
2.0
1.5
1.25A
1.0
3.4
3.3
15
10
5
0
3.4
3.3
3.2
3.2
Time (100µs/div)
Time (2ms/div)
Step-Down Converter Soft Start
Step-Down Converter Output
Voltage Error vs. Temperature
(VIN1 = 12V; VOUT1 = 3.3V)
15
10
5
0
4.0
2.0
0.0
Output Voltage Error (%)
20
Inductor Current
(bottom) (A)
Enable Voltage (top) (V)
Output Voltage (middle) (V)
(VIN1 = 12V; VEN1 = 10V; VOUT1 = 3.3V; IOUT1 = 2.5A)
1.0
IOUT1 = 0.1mA
IOUT1 = 1mA
IOUT1 = 1250mA
IOUT1 = 2500mA
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-50
-25
0
510
500
490
480
0
20
40
100
60
80
100
8
6
4
2
0
-2
-4
-6
-8
Temperature (°C)
6
75
(VOUT1 = 3.3V; IOUT1 = 2.5A)
Frequency Variation (%)
Switching Frequency (kHz)
(VIN1 = 12V; IOUT1 = 2.5A)
520
-20
50
Step-Down Converter Switching Frequency
vs. Input Voltage
Step-Down Converter Switching
Frequency vs. Temperature
-40
25
Temperature (°C)
Time (500µs/div)
470
Output Voltage
(bottom) (V)
2.5
Input Voltage
(top) (V)
2.5A
Output Current
(top) (A)
Output Voltage
(AC Coupled) (bottom) (V)
Step-Down Converter Load Transient Response
-40
-20
0
20
40
60
80
100
Temperature (°C)
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PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics
Step-Down Converter Input Current
vs. Input Voltage
LDO Dropout Voltage vs. Temperature
(VEN1 = VIN1)
1400
Dropout Voltage (mV)
Input Current (mA)
0.70
0.65
0.60
0.55
0.50
85°C
25°C
-40°C
0.45
0.40
6
9
12
15
18
21
1200
1000
IOUT2 = 600mA
IOUT2 = 500mA
IOUT2 = 300mA
IOUT2 = 150mA
IOUT2 = 50mA
800
600
400
200
0
24
-40
-20
0
Input Voltage (V)
20
40
60
80
100
Temperature (°C)
LDO Dropout Characteristics
LDO Dropout Voltage vs. Output Current
(VOUT2 = 1.8V)
1500
Dropout Voltage (mV)
Output Voltage (V)
1.84
1.82
1.80
1.78
IOUT2 = 0.1mA
IOUT2 = 10mA
IOUT2 = 50mA
IOUT2 = 100mA
IOUT2 = 300mA
IOUT2 = 600mA
1.76
1.74
1.72
1.70
1.5
900
600
300
0
2
2.5
3
3.5
4
85°C
25°C
-40°C
1200
4.5
0
100
Input Voltage (V)
200
300
400
500
600
Output Current (mA)
LDO Input Current vs. Input Voltage
LDO VIH and VIL vs. Input Voltage
(VEN1 = 0V; VEN2 = VIN2)
1.30
1.25
80
VIH and VIL (%)
Input Current (µA)
100
60
40
85°C
25°C
-40°C
20
0
2
2.5
3
3.5
4
4.5
1.20
1.15
1.10
5
1.00
2.5
Input Voltage (V)
2689.2008.06.1.0
VIH
VIL
1.05
3
3.5
4
4.5
5
5.5
Input Voltage (V)
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PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics
LDO Turn-On Time from Enable
(VIN2 = 3.3V; VEN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA)
3
2
2
1
0
2.0
1.0
Enable Voltage
(top) (V)
4
3
1
0
3
2
1
0.0
Output Voltage
(bottom) (V)
4
Output Voltage
(bottom) (V)
Enable Voltage
(top) (V)
LDO Turn-Off Response Time
(VIN2 = 3.3V; VEN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA)
0
-1.0
Time (5µs/div)
Time (5µs/div)
LDO Output Voltage Error vs. Temperature
LDO Load Transient Response
(VIN2 = 3.3V; VOUT2 = 1.8V)
(IOUT2 = 0.3A to 0.6A; VIN2 = 3.3V; VOUT2 = 1.8V; COUT2 = 2.2µF)
0.7
IOUT2 = 0.1mA
IOUT2 = 300mA
IOUT2 = 600mA
0.6
Output Current
(top) (A)
2.0
1.0
0.0
-1.0
0.5
0.4
0.3
1.90
1.85
Output Voltage
(bottom) (V)
Output Voltage Error (%)
3.0
1.80
-2.0
-3.0
-50
1.75
-25
0
25
50
75
100
Temperature (°C)
Time (40µs/div)
LDO Load Transient Response
LDO Line Transient Response
(IOUT2 = 0.06A to 0.6A; VIN2 = 3.3V; VOUT2 = 1.8V; COUT2 = 2.2µF)
(VIN2 = 3V to 4V; VOUT2 = 1.8V; IOUT2 = 600mA; COUT2 = 2.2µF)
0.4
0.2
0.0
0.06A
1.90
1.80
1.70
1.60
5
Input Voltage
(top) (V)
0.6A
Time (40µs/div)
8
4
VIN
3
2
VOUT
1.85
1.80
Output Voltage
(bottom) (V)
Output Current
(top) (A)
0.6
Output Voltage
(AC Coupled) (bottom) (V)
0.8
1.75
1.70
Time (200µs/div)
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PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics
LDO Output Voltage Noise
LDO Power Supply Rejection Ratio, PSRR
(IOUT2 = 10mA; Power BW: 300~50KHz)
(IOUT2 = 10mA; BW: 100KHz to 300KHz)
10
70
Magnitude (dB)
Noise (µVRMS)
60
5
50
40
30
20
10
0
100
1000
10000
100000
0
100
10000
100000
Frequency (Hz)
Frequency (Hz)
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1000
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PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Functional Block Diagram
VINT
Reg.
VL1
IN1
OT
FB1
Error
Amp
OSC
Comp.
Comp.
BST1
COMP1
Logic
LX1
Control
Logic
EN1
20Ω
Voltage
Ref
Ref1
Comp
VOCP1
= 0.1V
OT
RS1
OS1
IN2
OCP
FB_LDO
Error
Amp
VO2
Logic
FB_LDO
Voltage
Ref 2
EN2
Control
Logic
GND
Functional Description
The AAT2689 provides two independently regulated DC
outputs; consisting of a high voltage step-down (Buck)
regulator and a low input voltage linear low dropout
(LDO) regulator. The PMIC is optimized for low cost 12V
adapter inputs, making the device an ideal system-on-achip power solution for consumer communications
equipment.
Channel 1 is a step-down (Buck) regulator with an input
voltage range 6.0 to 24V; providing up to 2500mA output current. 490kHz fixed switching frequency allows
small L/C filtering components.
Channel 1 utilizes voltage mode control configured for
optimum performance across the entire output voltage
and load range. The controller includes integrated overcurrent, soft-start and over-temperature protection. Over-
10
current is sensed through the output inductor DC winding
resistance (DCR). An external resistor network adjusts
the current limit according to the DCR of the desired
inductor and the desired output current limit. Frequency
reduction limits over-current stresses during short-circuit
events. The operating frequency returns to the nominal
setting when over-current conditions are removed.
Channel 2 is a linear low-dropout (LDO) regulator providing up to 600mA output current at a factory set output
voltage. The device provides extremely low output noise,
low quiescent current and excellent transient response.
The controllers include integrated over-current, softstart and over-temperature protection. Independent
input and enable pins provide maximum design flexibility. The AAT2689 is available in the Pb-free 3x4mm
16-pin TDFN package. The rated operating temperature
range is -40°C to 85°C.
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2689.2008.06.1.0
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Applications Information
Output 1 is a high voltage DC/DC Buck (step-down) converter providing an output voltage from 1.5V to 5.5V.
The integrated high-side N-channel MOSFET device provides up to 2.5A output current. Input voltage range is
6.0V to 24.0V. The step-down converter utilizes constant
frequency (PWM-mode) voltage mode control to achieve
high operating efficiency while maintaining extremely
low output noise across the operating range. High
490kHz (nominal) switching frequency allows small
external filtering components, achieving minimum cost
and solution size. External compensation allows the
designer to optimize the transient response while achieving stability across the operating range.
Output 2 is a low voltage, low dropout (LDO) linear
regulator providing 1.8V with up to 600mA output current. The input voltage range is 2.7V to 5.5V. The LDO
provides very low noise output which can be derived
directly from the Output 1 channel.
Output Voltage and Current
Output 1 is set using an external resistor divider as
shown in Table 1. Minimum output voltage is 1.5V and
maximum output voltage is 5.5V. Typical maximum duty
cycle is 85%.
VOUT(V)
R4 = 6.04kΩ
R3(kΩ)
1.5
1.8
1.85
2.0
2.5
3.0
3.3
5.0
9.09
12.1
12.4
14.0
19.1
24.3
27.4
44.2
Two 22μF ceramic output capacitors are required to filter
the inductor current ripple and supply the load transient
current for IOUT = 2.5A. The 1206 package with 10V
minimum voltage rating is recommended for the output
capacitors to maintain a minimum capacitance drop with
DC bias.
Channel 1 Output Inductor Selection
The step-down converter utilizes constant frequency
(PWM-mode) voltage mode control. A 4.7μH inductor
value is selected to maintain the desired output current
ripple and minimize the converter’s response time to
load transients. The peak switch current should not
exceed the inductor saturation current, the MOSFET or
the external Schottky rectifier peak current ratings.
Channel 1 Rectifier Selection
When the high-side switch is on, the input voltage will be
applied to the cathode of the Schottky diode. The rectifier's rated reverse breakdown voltage must be chosen
at least equal to the maximum input voltage of the stepdown regulator.
When the high-side switch is off, the current will flow
from the power ground to the output through the
Schottky diode and the inductor. The power dissipation
of the Schottky diode during the time-off can be determined by the following equation:
PD = IOUT · VD · 1 -
VOUT
VIN
Where VD is the voltage drop across the Schottky diode.
Table 1: Feedback Resistor Values
Alternately, the feedback resistor may be calculated
using the following equation:
R3 =
Channel 1 Regulator
Output Capacitor Selection
(VOUT - 0.6) · R4
0.6
Channel 1 Input Capacitor Selection
For low cost applications, a 100μF/25V electrolytic capacitor is selected to control the voltage overshoot across
the high side MOSFET. A small ceramic capacitor with
voltage rating at least 1.05 times greater than the maximum input voltage is connected as close as possible to
the input pin (Pin 14) for high frequency decoupling.
R3 is rounded to the nearest 1% resistor value.
2689.2008.06.1.0
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11
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Channel 1 Feedback and
Compensation Networks
The feedback and compensation networks provide a
closed loop transfer function with the highest 0dB crossing frequency and adequate phase margin for system
stability. Equation 3, 4, 5 and 6 relate the compensation
network’s poles and zeros to the components R1, R3,
R5, C2, C3, and C8:
C3
C2
C8
R1
R5
VOUT1
COMP1
Eq. 3: FZ1 =
R3
1
2 · π · R1 · C2
FB1
R4
Eq. 4: FZ2 =
1
2 · π · (R 3 + R 5 ) · C 8
Eq. 5: FP1 =
1
REF
Figure 1: AAT2689 Feedback and Compensation
Networks for Type III Voltage-Mode Control Loop.
2 · π · R1 ·
The transfer function of the error amplifier is dominated
by the DC gain and the L COUT output filter of the regulator. This output filter and its equivalent series resistor
(ESR) create a double pole at FLC and a zero at FESR in the
following equations:
1
Eq. 1: FLC =
2 · π · L · COUT
Eq. 2: FESR =
Network
Feedback
Feed-forward
Compensation
Current Limit
Eq. 6: FP2 =
C2 · C3
C2 + C3
1
2 · π · R5 · C8
Components of the feedback, feed-forward, compensation, and current limit networks need to be adjusted to
maintain the systems stability for different input and
output voltages applications as shown in Table 2.
1
2 · π · ESR · COUT
Components
VOUT = 3.3V
VIN = 12V fixed
VOUT = 3.3V
VIN = 6V to 24V
VOUT = 5.0V
VIN = 6V to 24V
R3
R4
C8
R5
C2
C3
R1
C7
R2
R6
R7
R8
6.04kΩ
27.4kΩ
470pF
1.37kΩ
1nF
56pF
11.8kΩ
22nF
10kΩ
Open
11kΩ
600kΩ
6.04kΩ
27.4kΩ
330pF
499Ω
470pF
56pF
24.3kΩ
220nF
2kΩ
Open
2kΩ
133kΩ
6.04kΩ
44.2kΩ
330pF
499Ω
220pF
56pF
24.3kΩ
220nF
2kΩ
Open
2kΩ
133kΩ
Table 2: AAT2689 Feedback, Feed-Forward, Compensation, and Current Limit Components
for VOUT = 3.3V and VOUT = 5.0V.
12
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2689.2008.06.1.0
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Channel 1 Thermal Protection
The AAT2689 has an internal thermal protection circuit
which will turn on when the device die temperature
exceeds 135°C. The internal thermal protection circuit
will actively turn off the high side regulator output device
to prevent the possibility of over temperature damage.
The Buck regulator output will remain in a shutdown
state until the internal die temperature falls back below
the 135°C trip point. The combination and interaction
between the short circuit and thermal protection systems allows the Buck regulator to withstand indefinite
short-circuit conditions without sustaining permanent
damage.
VOUT1
3.3V/2.5A
L1
LX1
4.7μH 5.3A
R2
2k
RS1
4
C7
220nF
R6
R7
OS1
5
Over-Current Protection
The Output 1 controller provides true-load DC output
current sensing which protects the load and limits component stresses. The output current is sensed through
the DC resistance in the output inductor (DCR). The controller reduces the operating frequency when an overcurrent condition is detected; limiting stresses and preventing inductor saturation. This allows the smallest
possible inductor for a given output load. A small resistor
divider may be necessary to adjust the over-current
threshold and compensate for variation in inductor DCR.
The preset current limit threshold is triggered when the
differential voltage from RS1 to OS1 exceeds 100mV
(nominal).
L1
LX1
4.7μH 5.3A
R2
2k
RS1
V OUT1
3.3V/2.5A
C7
220nF
4
R7
OS1
5
R8
Figure 2: Resistor Network to Adjust the Current
Limit Less than the Pre-Set Over-Current
Threshold (Add R7, R8).
2689.2008.06.1.0
Figure 3: Resistor Network to Adjust the Current
Limit Greater than the Pre-Set Over-Current Level
(Add R6, R7).
Channel 2 Input Capacitor
Typically, a 1μF or larger capacitor is recommended for
CIN in most applications. A CIN capacitor is not required for
basic LDO regulator operation. However, if the AAT2689
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 close to the device VIN pin as possible. CIN values greater than 1μF 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.
Channel 2 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 connected as close as possible for
maximum device performance. The AAT2689 LDO has
been specifically designed to function with very low ESR
ceramic capacitors. For best performance, ceramic
capacitors are recommended.
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13
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical output capacitor values for maximum output current conditions range from 1μF to 10μF. Applications
utilizing the exceptionally low output noise and optimum
power supply ripple rejection characteristics of channel
2 should use 2.2μF 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 0.47μF.
Channel 2 No-Load Stability
Channel 2 Enable Function
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.
The AAT2689 features an LDO regulator enable/disable
function. This pin (EN) is active high and is 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 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. When the LDO regulator is in
shutdown mode, an internal 1.5kΩ resistor is connected
between VOUT and GND. This is intended to discharge
COUT when the LDO regulator is disabled. The internal
1.5kΩ has no adverse effect on device turn-on time.
Channel 2 Short-Circuit Protection
The AAT2689 LDO contains an internal short-circuit protection circuit 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.
Channel 2 Thermal Protection
The AAT2689 LDO has an internal thermal protection
circuit which will turn on when the device die temperature exceeds 150°C. 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 150°C trip point. The combination and
interaction between the short circuit and thermal protection systems allows the LDO regulator to withstand
indefinite short-circuit conditions without sustaining permanent damage.
14
The AAT2689 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.
Channel 2 Reverse Output-to-Input
Voltage Conditions and Protection
Thermal Calculations
There are three types of losses associated with the
AAT2689 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 synchronous step-down converter and LDO losses is given by:
PTOTAL =
IOUT12 · (RDS(ON)H · VOUT1 + RDS(ON)L · [VIN1 - VOUT1])
VIN1
+ (tSW · FS · IOUT1 + IQ1) · VIN1 + (VIN2 - VOUT2) · IOUT2
IQ1 and IQ2 are the step-down converter and LDO quiescent currents respectively. The term tSW is used to estimate the full load step-down converter switching losses.
www.analogictech.com
2689.2008.06.1.0
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
For asynchronous step-down converter operation, the
power dissipation is only in the internal high side MOSFET
during the on time. When the switch is off, the power
dissipates on the external Schottky diode. Total package
loss for AAT2689 reduces to the following equation:
PTOTAL = IOUT12 · RDS(ON)H · D + (tSW · FS · IOUT1 + IQ1) · VIN1 + (VIN2 - VOUT2) · IOUT2
where D =
VOUT
is the duty cycle.
VIN
2.
3.
4.
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be investigated over the complete input voltage range.
Given the total losses, the maximum junction temperature can be derived from the θJA for the TDFN34-16
package, which is 50°C/W.
5.
6.
TJ(MAX) = PTOTAL · θJA + TAMB
Layout Considerations
The suggested PCB layout for the AAT2689 is shown in
Figures 4, 5, and 6. The following guidelines should be
used to help ensure a proper layout.
1.
The power input capacitors (C1 and C15) should be
connected as close as possible to high voltage input
pin (IN1) and power ground.
2689.2008.06.1.0
7.
8.
C1, L1, D2, C9 and C11 should be placed as close as
possible to minimize any parasitic inductance in the
switched current path which generates a large voltage spike during the switching interval. The connection of inductor to switching node should be as short
as possible.
The feedback trace or FB1 pin should be separated
from any power trace and connected as close as possible to the load point. Sensing along a high-current
load trace will degrade DC load regulation.
The resistance of the trace from the load returns to
PGND should be kept to a minimum. This will help to
minimize any error in DC regulation due to differences in the potential of the internal signal ground
and the power ground.
Connect unused signal pins to ground to avoid
unwanted noise coupling.
The critical small signal components include feedback components, and compensation components
should be placed close to the FB1 and COMP1 pins.
The feedback resistors should be located as close as
possible to the FB1 pin with its ground tied straight
to the signal ground plane which is separated from
power ground plane.
C7 should be connected close to the RS1 and OS1
pins, while R2 should be connected directly to the
output pin of the inductor. For the best current limit
performance, C7 and R2 should be placed on the bottom layer to avoid noise coupling from the inductor.
For good thermal coupling, PCB vias are required
from exposed pad 1 (EP1) to the bottom ground
plane and from exposed pad 2 (EP2) to the bottom
VIN plane.
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15
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
C4
0.1μF
2
LX1
16
VL1
LX1
15
12
1
V IN1
C6
2.2μF
6.0V - 24.0V
IN1
RS1
4
OS1
5
1
D2
C7
R6 220nF
open
R2
2k
R7
2k
EP2
14
IN1
3
2
EN1
FB1
7
COMP1
6
+
C15
1μF
25V
R5
499
C9
C11 C12, C13
22μF 22μF open
OUT2
10
R1 24.3k
1
C1
100μF
25V
R3
27.4k
AAT2689
3
EN1
C8
330pF
4.7μH/5.3A
D1
BAS16
2
J1
V OUT1
3.3V/2.5A
L1
U1
BST1
V IN2
9
IN2
8
EN 2
C5
2.2μF
2
EN2
1
VOUT2
1.8V/600mA
EP1
11
AGND GND
TDFN34-16
U1
C1
C5, C6, C10
C4
C2, C3, C7, C8
C9, C11
D1
D2
L1
R1 - R8
C15
C2
470pF
C3
56pF
3
R8
133k
R4
6.04k
13
C10
2.2μF
C14
open
AAT2689 Analogic Technologies, Hi-Voltage Buck/LDO, TDFN34-16
Cap, MLC, 100μF/25V, Electrolytic cap
Cap, MLC, 2.2μF, 6.3V, 0805
Cap, MLC, 0.1μF/6.3V, 0603
Cap, MLC, misc., 0603
Cap, MLC, 22μF/10V, 1206
BAS16, Generic, Rectifier, 0.2A/85V, Ultrafast, SOT23
B340A, Generic, Schottky Rectifier, 3A/40V, SMA
RCH108NP-4R7M, 4.7μF, ISAT = 5.3A, DCR = 11.7mΩ or Wurth 744 778 900 4, 4.7μH, ISAT = 3.9A, DCR = 35mΩ
Carbon film resistor, 0402
Cap, MLC,1μF/25V, 0603
Figure 4: AAT2689IRN Evaluation Board Schematic For VIN = 6V to 24V and VOUT = 3.3V.
Figure 5: AAT2689IRN Evaluation
Board Top Layer.
16
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Figure 6: AAT2689IRN Evaluation
Board Bottom Layer.
2689.2008.06.1.0
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
AAT2689 Design Example
Specifications
VO1 = 3.3V @ 2.5A, Pulsed Load ΔILOAD = 2.5A
VO2 = 1.8V @ 600mA
VIN1 = 12V
FS = 490kHz
TAMB = 85°C in TDFN34-16 Package
Channel 1 Output Inductor
For Sumida inductor RCH108NP-4R7M, 4.7μH, DCR = 11.7mΩ max.
ΔI =
VOUT1
VOUT1
3.3V
3.3V
· 1=
· 1= 1A
L1 · FS
VIN
4.7μH · 490kHz
12V
IPK1 = IOUT1 +
ΔI
= 2.5A + 1A = 3.5A
2
PL1 = IOUT12 · DCR = 3.5A2 · 11.7mΩ = 143mW
Channel 1 Output Capacitor
VDROOP = 0.33V (10% Output Voltage)
COUT =
3 · ΔILOAD
3 · 2.5A
=
= 46.4μF; use 2x22μF
0.33V · 490kHz
VDROOP · FS
IRMS(MAX) =
1
2· 3
·
VOUT1 · (VIN(MAX) - VOUT1)
1
3.3V · (24V - 3.3V)
·
= 357mARMS
=
4.7μH
· 490kHz · 24V
L · FS · VIN1(MAX)
2· 3
PRMS = ESR · IRMS2 = 11.7mΩ · (357mA)2 = 1.5W
Channel 1 Input Capacitor
Input Ripple VPP = 25mV
CIN1 =
1
VPP1
- ESR · 4 · FS
IOUT1
=
1
25mV
- 5mΩ · 4 · 490kHz
2.5A
= 102μF
For low cost applications, 100μF/25V electrolytic capacitor in parallel with 1μF/25V ceramic capacitor are used to reduce
the ESR.
IRMS =
IOUT1
= 1.25A
2
P = ESR · (IRMS)2 = 5mΩ · (1.25A)2 = 7.8mW
2689.2008.06.1.0
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17
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Channel 1 Current Limit
Voltage sense VS = 100mV
Total trace parasitic resistor and inductor DCR is 10mΩ
ILIM =
VS
100mV
=
= 10A > 5A
10mΩ
DCR
R8 =
VOUT1 · R2
3.3V · 2kΩ
= 133kΩ
=
0.1V - 5A · 10mΩ
VOCP - ILIMIT · DCR
R7 =
R2 · R 8
2kΩ · 133kΩ
=
= 2kΩ
133kΩ - 2kΩ
R8 - R 2
AAT2689 Losses
All values assume a 25°C ambient temperature and thermal resistance of 50°C/W in the TDFN34-16 package.
PTOTAL = IOUT12 · RDS(ON)H · D + (tSW · FS · IOUT1 + IQ1) · VIN1 + (VIN2 - VOUT2) · IOUT2
2
PTOTAL = 2.5A · 70mΩ · 3.3V + (5ns · 490kHz · 2.5A + 70μA) · 12V · (3.3V - 1.8V) · 600mA
12V
PTOTAL = 1.1W
TJ(MAX) = TAMB + ΘJA · PLOSS = 25°C + (50°C/W) · 1.1W = 80°C
18
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2689.2008.06.1.0
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Ordering Information
Voltage
Package
Channel 1
Channel 2
Marking1
Part Number (Tape and Reel)2
TDFN34-16
Adj (0.6)
1.8
3PXYY
AAT2689IRN-AI-T1
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.
Legend
Voltage
Code
Adjustable (0.6)
1.8
A
I
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
2689.2008.06.1.0
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19
PRODUCT DATASHEET
AAT2689
SystemPowerTM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Package Information1
TDFN34-16
1.600 ± 0.050
0.35 REF
0.450 ± 0.050
0.230 ± 0.050
4.000 ± 0.050
Index Area
2.350 ± 0.050
0.070 ± 0.050
3.000 ± 0.050
0.25 REF
0.430 ± 0.050
1.600 ± 0.050
Top View
0.750 ± 0.050
Bottom View
0.230 ± 0.050
0.050 ± 0.050
Side View
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.
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3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© 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.
20
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