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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
General Description
The AAT2688 provides two independently regulated DC outputs: a high voltage synchronous step-down (Buck) regulator and a low input voltage step-down low dropout (LDO) regulator. The PMIC is optimized for low cost 12V adapter inputs, making the device the ideal system-ona-chip power solution for consumer communications equipment. Channel 1 is a step-down regulator with an input voltage range of 6.0V to 24V, providing up to 4.5A 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 low output noise, low quiescent current, and excellent transient response. The step-down regulator includes integrated over-current, soft-start and over-temperature protection. Independent input and enable pins provide maximum design flexibility. The AAT2688 is available in the Pb-free 4mm x 5mm 24-pin TQFN package. The rated operating temperature range is -40C to 85C.
Features
* 2-Output Step-Down Converters: * Channel 1 (Buck): VIN1 = 6.0 to 24.0V VOUT1 Adjustable from 0.8V to 5.5V IOUT1 up to 4.5A High Switching Frequency Voltage Mode Control High Accuracy 1.5% PWM Fixed Frequency for Low Ripple * Channel 2 (LDO): VIN2 = 2.7V to 5.5V IOUT2 up to 600mA 1V Dropout Voltage at 600mA IOUT * Small Solution Size * System on a Chip * Ultra-small External L/C * Shutdown Current <35A * Independent Enable Pins * Over-Current and Over-Temperature Protection * Internal Soft Start * 4x5mm 24-Pin TQFN Low Profile Package * -40C to 85C Temperature Range
Applications
* * * * DSL and Cable Modems Notebook Computers Satellite Set-top Boxes Wireless LAN Systems
Typical Application
L1 4.7H/5.3A C3 0.1F D1 BAS16 J1 VIN1 6.0V -24.0V
2 1
VOUT1 3.3V/4.5A
LX1 BST1 VL1 DL Q1 R2 2K RS1 OS1 IN1 FB1 COMP1 R1 3.92k C5 2.2nF C6 150pF OUT2 C12 2.2F VOUT2 R4 1.96k R5 150 C4 220nF C10 2.2nF
R3 9.09k
C14 2.2F
C7 22F
C8 22F
C9 22F
AAT2688
EN1 VIN2 + C1 220F 25V C13 1F 25V C2 2.2F IN2
EN2
GND TQFN45-24
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Pin Descriptions
Pin #
1, 2, 23, 24 3, 4, 9, 12 5 6 7 8 10 11 13 14 15 16 17 18, 19 20 21 22 EP
Symbol
LX1 N/C BST1 EN1 GND2 EN2 IN2 OUT2 RS1 OS1 COMP1 FB1 GND1 VL1 DL1 PGND IN1 EP
Function
Channel 1 step-down (Buck) converter switching pin. Connect output inductor to this pin. Connect both LX1 pins together. No connect. For optional routing reasons, pins 3 and 4 can be connected to VIN, pin 9 to pin 10 (IN2), and pin 12 to pin 11 (OUT2). Channel 1 step-down 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 (LX1) for internal hi-side MOSFET gate drive. Channel 1 step-down regulator enable input pin. Active high enables internal linear regulator and channel 1 output. Ground pin for Channel 2. Power return pin for channel 2. Connect return of channel 2 input and output capacitors close to this pin for best noise performance. Channel 2 low dropout (LDO) enable input pin. Active high. Input supply voltage pin for channel 2 linear low dropout (LDO) regulator. Connect 2.2F ceramic input capacitor close to this pin. Output of channel 2 of linear low dropout (LDO) regulator. Connect a 2.2F ceramic capacitor from this pin to GND pin. Channel 1 output current sense pin. Connect a small signal resistor from this pin to switching node (LX1) to enable over-current sense for step-down converter. The current limit threshold varies with sense resistor sizing. Channel 1 output sense voltage pin. Connect to the output capacitor to enable over-current sense for step-down converter. Compensation pin for channel 1 step-down regulator. Connect a series resistor, capacitor network to compensate the voltage mode control loop. Feedback input pin for channel 1 step-down converter. Connect an external resistor divider to this pin to program the output voltage to the desired value. Ground pin for channel 1. Power return pin for channel 1. Connect return of channel 1 input and output capacitors close to this pin for best noise performance. Internal linear regulator. Connect a 2.2F capacitor from this pin to GND pin. Channel 1 gate drive for low side MOSFET. Connect to the gate pin of an external N type MOSFET (see the "MOSFET Selection" section of this product datasheet). 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 regulator. Connect both IN1 pins together. Connect the input capacitor close to this pin for best noise performance. Exposed Paddle. Tie to IN1. Connect to PCB heatsink for optimum thermal performance.
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2688.2008.06.1.0
PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Pin Configuration
TQFN45-24 (Top View)
DL1 PGND IN1 LX1 LX1
24 23 22 21 20
LX1 LX1 N/C N/C BST1 EN1 GND2
1 2 3 4 5 6 7
19 18 17
EP
16 15 14 13
VL1 VL1 GND1 FB1 COMP1 OS1 RS1
10
11
12
8
9
N/C OUT2 IN2 N/C EN2
Absolute Maximum Ratings1
Symbol
VIN(HI) VIN(LO) VBST1-LX1 VCONTROL VEN2 TJ TLEAD
Description
IN1, EN1, LX1 to GND IN2, VL1 to GND BST1 to LX1 FB1, COMP1, RS1, OS1, OUT2, DL1 to GND EN2 to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-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 -40 to 150 300
Units
V V V V V C C
Thermal Information
Symbol
PD JA
Description
Maximum Power Dissipation2 Thermal Resistance3
Value
3.0 33
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 with exposed paddle connected to ground plane. 3. Derate 30mW/C above 25C ambient temperature.
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Electrical Characteristics1
VIN1 = 12.0V, VIN2 =3.3V; TA = -40C to 85C, unless otherwise noted. Typical values are at TA = 25C. Symbol Description Conditions Min
6.0 VIN1 Rising VIN1 Hysteresis VIN1 Falling 300 3.0 0.8 0.576 -3.0 5.5 0.594 +3.0
Typ
Max
24.0 5.0
Units
V V mV V V V % %/V %/A
Channel 1: 4.5A Step-Down (Buck) Converter VIN1 Input Voltage VUVLO1 VOUT1 VFB1 VOUT (VOUT/VOUT)/ VIN (VOUT/VOUT)/ IOUT IQ1 ISHDN1 VOCP1 ILX1 DMAX RDL1 UVLO Threshold Output Voltage Range Feedback Pin Voltage Output Voltage Accuracy Line Regulation Load Regulation Quiescent Current Shutdown Current Over-Current Offset Voltage LX1 Pin Leakage Current Maximum Duty Cycle Low Side Drive Source Resistance
0.585 0.05 0.2 600
IOUT1 = 0 to 4.5A VIN1 = 6V to 24V, VOUT1 = 3.3V, IOUT1 = 4.5A VIN1 = 12V, VOUT1 = 3.3V, IOUT1 = 0A to 4.5A VEN1 = Low, No load, VFB1 = 1.2V VEN1 = High, VL1 = 0V VEN1 = Low, VIN1 = 6.0V to 24.0V, TA = 25C VIN1 = 24.0V, VEN1 = 5.0V Pull-Up, VL1 = 4.5V Pull-Down, VL1 = 4.5V VL1 = 4.5V
80 -1.0
100 85 5.0 1.7 35 490 100 2.5
35 120 1.0
A A mV A %
RDSON(H) Hi Side On-Resistance 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 Low Dropout (LDO) Regulator Input Voltage VIN2 VDO2 Dropout Voltage 98% * VOUT2(NOM), IOUT2 = 600mA IQ2 Quiescent (Ground) Current No load ISHDN2 Shutdown Current VEN2 = GND IOUT2= 1mA to 600mA, VIN2 = 2.7 to 5.5V, TA = 25C Output Voltage Tolerance VOUT2(TOL) IOUT2= 1mA to 600mA, VIN2 = 2.7 to 5.5V, TA = -40C to 85C eN Output Noise BW = 300Hz to 50kHz 1kHz PSRR Power Supply Rejection Ratio IOUT2 = 10mA 10kHz 1MHz Current Limit ILIMIT2 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 Enable Threshold Low VEN1,EN2(L) VEN1(H) Enable Threshold High VEN2(H) IEN1,EN2 Input Low Current
350
650
m kHz kHz ms V mV A A
2.7 1000 70 -2.0 -3.5 250 67 47 45 800 15 135 15
5.5 1300 125 1.0 +2.0 +3.5
%
% VRMS dB mA s C C
700
0.6 2.5 1.4 -1.0
V V
1.0
A
1. The AAT2688 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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2688.2008.06.1.0
PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics-Channel 1
Step-Down Converter Efficiency vs. Output Current
(VOUT1 = 3.3V; L = 4.7H)
100 90 80 2.0
Step-Down Converter DC Regulation
(VOUT1 = 3.3V; L = 4.7H) Output Voltage Error (%)
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.1
Efficiency (%)
70 60 50 40 30 20 10 0 0.1 1 10 100
VIN1 = 6V VIN1 = 8V VIN1 = 12V VIN1 = 18V VIN1 = 24V
1000 10000
VIN1 = 6V VIN1 = 8V VIN1 = 12V VIN1 = 18V VIN1 = 24V
1 10 100 1000 10000
Output Current (mA)
Output Current (mA)
Step-Down Converter Output Voltage Error vs. Input Voltage
(VOUT1 = 3.3V; L = 4.7H) Output Voltage Error (%)
Switching Frequency (kHz)
2
Step-Down Converter Switching Frequency vs. Temperature
(VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 4.5A)
510
1
IOUT1 = 0.10mA IOUT1 = 100mA IOUT1 = 1000mA IOUT1 = 2250mA IOUT1 = 3500mA IOUT1 = 4500mA
500
0
490
-1
480
-2 6 8 10 12 14 16 18 20 22 24
470 -40
-15
10
35
60
85
Input Voltage (V)
Temperature (C)
Step-Down Converter Switching Frequency vs. Input Voltage
Switching Frequency Variation (%)
No Load Step-Down Converter Input Current vs. Input Voltage
(VEN1 = VIN1)
0.70
(VOUT1 = 3.3V; IOUT1 = 4.5A)
3 2 1 0 -1 -2 -3 6 8 10 12 14 16 18 20 22 24
Input Current (mA)
0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30
85C 25C -40C
Input Voltage (V)
Input Voltage (V)
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics-Channel 1
Step-Down Converter Output Voltage Error vs. Temperature
(VIN1 = 12V; VOUT1 = 3.3V) Output Voltage Error (%)
0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -40
Step-Down Converter Output Ripple
(VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 4.5A) LX Voltage (middle) (V) Inductor Current (bottom) (A)
3.31 3.30
Output Voltage (top) (V)
IOUT1 = 0.10mA IOUT1 = 10mA IOUT1 = 2250mA IOUT1 = 4500mA
3.29 12V 0V 5 4 3
-15
10
35
60
85
Temperature (C)
Time (1s/div)
Step-Down Converter Output Ripple
(VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 1mA) LX Voltage (middle) (V) Inductor Current (bottom) (A)
3.31 3.30
Step-Down Converter Load Transient Response
(IOUT1 = 3.375A to 4.5A; VIN1 = 12V; COUT1 = 3x22F) Output Voltage (bottom) (V)
6
Output Current (top) (A)
4.5A 3.375A
5 4 3
Output Voltage (top) (V)
3.29 12V 0V 1 0 -1
3.4 3.3 3.2
Time (1s/div)
Time (100s/div)
Step-Down Converter Load Transient Response
(IOUT1 = 2.25 to 4.5A; VIN1 = 12V; COUT1 = 3x22F) Output Voltage (bottom) (V)
Step-Down Converter Load Transient Response
(IOUT1 = 0.45A to 4.5A; VIN1 = 12V; COUT1 = 3x22F) Output Voltage (bottom) (V)
4.5A 6
Output Current (top) (A)
Output Current (top) (A)
4.5A
5 4
4 0.45A 2 0 3.7 3.5 3.3 3.1 2.9
2.25A
3 2
3.5 3.3 3.1
Time (100s/div)
Time (100s/div)
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2688.2008.06.1.0
PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics-Channel 1
Step-Down Converter Line Transient Response
(VIN1 = 6V to 10V; VOUT1 = 3.3V; IOUT1 = 4.5A)
15 10 5
Step-Down Converter Soft Start
(VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 4.5A) Enable Voltage (top) (V) Output Voltage (middle) (V)
15 10
Output Voltage (bottom) (V)
Input Voltage (top) (V)
Output Current (bottom) (A)
5 0 6 4 2 0
3.35 3.30 3.25
Time (100ms/div)
Time (500s/div)
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics-Channel 2
LDO Input Current vs. Input Voltage
(VEN1 = 0V; VEN2 = VIN2)
100 1400
LDO Dropout Voltage vs. Temperature
Dropout Voltage (mV)
Input Current (A)
1200 1000 800 600 400 200 0 -40
80
60
40
IOUT2 = 600mA IOUT2 = 500mA IOUT2 = 300mA IOUT2 = 150mA IOUT2 = 50mA
20
85C 25C -40C
2 2.5 3 3.5 4 4.5 5
0
-15
10
35
60
85
Input Voltage (V)
Temperature (C)
LDO Dropout Voltage vs. Output Current
1500
1.30 1.25
LDO VIH and VIL vs. Input Voltage
Dropout Voltage (V)
1200
VIH and VIL (V)
1.20 1.15 1.10 1.05 1.00
900
600
300
85C 25C -40C
0 100 200 300 400 500 600
VIH VIL
2.5 3 3.5 4 4.5 5 5.5
0
Output Current (mA)
Input Voltage (V)
LDO Output Voltage Error vs. Temperature
(VIN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA)
3.0 1.84
LDO Dropout Characteristics
(VOUT2 = 1.8V)
Output Voltage Error (%)
Output Voltage (V)
2.0 1.0 0.0 -1.0 -2.0 -3.0 -50 -25 0 25 50
IOUT2 = 0.1mA IOUT2 = 300mA IOUT2 = 600mA
1.82 1.80 1.78 1.76 1.74 1.72 1.70 1.5
IOUT2 = 0.1mA IOUT2 = 50mA IOUT2 = 100mA IOUT2 = 300mA IOUT2 = 600mA
2 2.5 3 3.5 4 4.5
75
100
Temperature (C)
Input Voltage (V)
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2688.2008.06.1.0
PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Typical Characteristics-Channel 2
LDO Turn-Off Response Time
(VIN2 = 3.3V; VEN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA)
4 4
LDO Turn-On Time from Enable
(VIN2 = 3.3V; VEN2 = 3.3V; VOUT2 = 1.8V; IOUT2 = 600mA) Output Voltage (bottom) (V) Output Voltage (bottom) (V) Enable Voltage (top) (V)
3 2 1 0 3 2 1 0
Enable Voltage (top) (V)
3 2 1 0 2.0 1.0 0.0 -1.0
Time (5s/div)
Time (5s/div)
LDO Line Transient Response
(VIN2 = 3V to 4V; VOUT2 = 1.8V; IOUT2 = 600mA; COUT2 = 2.2F) Output Voltage (bottom) (V) Input Voltage (top) (V)
5 4 3 2 VOUT 1.85 1.80 1.75 1.70 0.7
LDO Load Transient Response
(IOUT2 = 0.3 to 0.6A; VIN2 = 3.3V; VOUT2 = 1.8V; COUT2 = 2.2F) Output Voltage (bottom) (V) Output Current (top) (A)
0.6 0.5 0.4 0.3
VIN
1.85 1.80 1.75
Time (200s/div)
Time (40s/div)
LDO Output Voltage Noise
(IOUT2 = 10mA; Power BW: 300~50KHz)
10
LDO Power Supply Rejection Ratio, PSRR
(IOUT2 = 10mA; BW: 100KHz to 300KHz)
70 60
Magnitude (dB)
Noise (VRMS)
50 40 30 20 10
5
0 100
1000
10000
100000
0 100
1000
10000
100000
Frequency (Hz)
Frequency (Hz)
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Functional Block Diagram
VINT
VL1
Reg.
IN1
OT OSC
FB 1
Comp. . Comp Error Amp 30m
BST1
COMP1
Logic
Control Logic Voltage Ref
20
EN 1
LX1
PGND
DL1 RS1 OS1
GND1
Comp
OT
IN 2
OCP FB_LDO Error Amp
OUT 2 Logic
FB_LDO
Voltage Ref 2
EN2
Control Logic
GND2
Functional Description
The AAT2688 provides two independently regulated DC outputs; consisting of a high voltage synchronous stepdown (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 the ideal system-on-a-chip 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 4.5A 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 regulator includes integrated overcurrent, soft-start and over-temperature protection. Over-current is sensed through the output inductor DC
winding resistance. An external resistor network adjusts the current limit according to the DC winding resistance 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 low-dropout (LDO) regulator providing up to 600mA output current at a factory set output voltage. The device provides low output noise, low quiescent current, and excellent transient response. The regulators include integrated over-current, soft-start and over-temperature protection. Independent input and enable pins provide maximum design flexibility. The AAT2688 is available in the Pb-free 4x5 mm 24-pin TQFN package. The rated operating temperature range is -40C to 85C.
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2688.2008.06.1.0
PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Applications Information
Output 1 is a high voltage DC/DC step-down converter providing an output voltage from 0.8V to 5.5V. The integrated high-side N-channel MOSFET device provides up to 4.5A 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 and an optional feed forward capacitor 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 Output 1.
Channel 1 Regulator Output Capacitor Selection
Three 22F ceramic output capacitors are required to filter the inductor current ripple and supply the load transient current for IOUT = 4.5A. 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 4.7H 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 or the MOSFETs.
Channel 1 MOSFET Selection
The step-down (buck) converter utilizes synchronous rectification (Q1) for constant frequency (PWM mode) voltage mode control. The synchronous rectifier is selected based on the desired RDS(ON) value and QG (total gate charge), these two critical parameters are weighed against each other. To get a low RDS(ON) value, the MOSFET must be of a very large size and a larger MOSFET will have a large QG. Conversely to get a low QG, the MOSFET must be small and thus have a large RDS(ON) value. In addition to the trade off between RDS(ON) and QG, the maximum voltage rating for the external synchronous MOSFET must exceed the maximum application input voltage value (VDS[MAX] > VIN[MAX]). The QG affects the turn-on/turn-off time of the synchronous MOSFET, the longer the turn-on/turn-off time the more likely the step-down converter will have "shoot through" current issues. "Shoot through" current occurs when the AAT2688 internal top-side MOSFET and the external synchronous MOSFET are conducting current at the same time. This will result in a low impedance path to ground from the input voltage through the two MOSFETs, and the current may exceed the maximum current rating of the AAT2688 and external synchronous MOSFET. Exceeding the maximum current ratings will lead to the destructive derating of the AAT2688 and external synchronous MOSFET.
Output Voltage--Channel 11
The output voltage is set using an external resistor divider as shown in Table 1. Minimum output voltage is 0.8V and maximum output voltage is 5.5V. Typical maximum duty cycle is 85%. Example: with R4 = 1.96K,
R3 =
(VOUT - 0.585) * R4 0.585
VOUT1 (V)
0.8 1.0 1.2 1.5 1.8 2.0 2.5 3.0 3.3 5.0
R3 (k)
0.715 1.37 2.05 3.09 4.02 4.75 6.49 8.06 9.09 14.7
Table 1: External Resistor Values (Standard 1% Resistors are Substituted for Calculated Values).
1. The R3 and R4 feedback resistors are separate from the compensation network. When changing either R3 and/or R4, the compensation network will have to be altered. Contact the Applications Engineering department for compensation network recommendations for specific output voltages.
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
The critical parameter recommendations for the external synchronous minimum 25V MOSFET are as follows: QG (Total Gate Charge) = 5nC to 15nC (max) (VGS: 4.5V to 5V) RDS(ON) = 10m to 30m (max) (VGS: 4.5V to 5V) Eq. 3: FZ1 = Eq. 4: FZ2 = Eq. 5: FP1 =
1 2 * * R1 * C5
1 2 * * (R3 + R5) * C10
1
Channel 1 Input Capacitor Selection
For low cost applications, a 220F/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.
2 * * R1 *
Eq. 6: FP2 =
C5 * C6 C5 + C6
1 2 * * R5 * C10
Channel 1 Feedback and Compensation Networks
C6
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 voltage applications as shown in Table 2. VOUT =3.3V VIN=6V-24V
1.96k 9.09k 2.2nF 150 2.2nF 150pF 3.92k 220nF 2k Open 0 Open
Network
C5 R1 C10 R5 VOUT1
Components
R4 R3 C10 R5 C5 C6 R1 C4 R2 R6 R7 R8
Feedback Feed Forward
COMP1 R3
Compensation
FB1 R4
Current Limit
REF
Figure 1: AAT2688 Feedback and Compensation Networks for Type III Voltage-Mode Control Loop. 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: Eq. 1: FLC = Eq. 2: FESR =
Table 2: AAT2688 Feedback, Compensation, and Current Limit Components for VOUT =3.3V.
Channel 1 Thermal Protection
The AAT2688 has an internal thermal protection circuit which will turn on when the device die temperature exceeds 135C. 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 135C 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.
1 2 * * L * COUT
1 2 * * ESR * COUT
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, C5, C6, and C10:
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Over-Current Protection
The regulator 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. The regulator reduces the operating frequency when an over-current condition is detected; limiting stresses and preventing inductor saturation. This allows the smallest possible inductor for the given application. A small resistor divider may be necessary to adjust the over-current threshold and compensate for variation in inductor DC resistance.
Channel 2 Input Capacitor
Typically, a 1F or larger capacitor is recommended for CIN in most applications. A CIN capacitor is not required for basic LDO regulator operation. However, if the AAT2688 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 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.
L1 LX1 4.7H
V OUT1 3.3V/4.5A
R2 2k RS1
C4 220nF R7
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 AAT2688 LDO 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. Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteristics of the channel 2 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.
OS1 R8
Figure 2: Resistor Network to Adjust the Current Limit Less than the Pre-Set Over-Current Threshold (Add R7, R8).
L1 LX1 4.7H
VOUT1 3.3V/4.5A
R2 2k RS1 OS1
C4 220nF R6 R7
Channel 2 Enable Function
The AAT2688 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 the disable shutdown mode when the voltage on the EN pin falls below 0.6V. If the enable function is not needed in a specific application, it may be tied to VIN to keep the LDO regulator in a continuously on state. When the LDO regulator is in shut-
Figure 3: Resistor Network to Adjust the Current Limit Greater than the Pre-Set Over-Current Level (Add R6, R7).
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
down mode, an internal 1.5k resistor is connected between VOUT and GND. This is intended to discharge COUT when the LDO regulator is disabled. The internal 1.5k has no adverse effect on device turn-on time. highly recommended. A larger value of CIN with respect to COUT will affect 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.
Channel 2 Short-Circuit Protection
The AAT2688 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.
Thermal Calculations
There are three types of losses associated with the AAT2688 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:
Channel 2 Thermal Protection
The AAT2688 LDO has an internal thermal protection circuit which will turn on when the device die temperature exceeds 135C. 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 135C 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.
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. For a synchronous Step-Down converter, the power dissipation occurs in the internal high side MOSFET during the on time and the external low side MOSFET during the off time. When the internal high side switch is off, the power dissipates on the external low side switch. The total package losses for AAT2688 reduce to the following equation:
PTOTAL = IOUT12 * RDS(ON)H * D + (tSW * FS * IOUT1 + IQ1) * VIN + (VIN2 - VOUT2) * IOUT2
Channel 2 No-Load Stability
The AAT2688 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
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
Where: D = VOUT is the duty cycle. 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 TQFN45-24 package, which is 33C/W.
TJ(MAX) = PTOTAL * JA + TAMB
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Layout Considerations
The suggested PCB layout for the AAT2688 is shown in Figures 5 through 8. 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. C1, L1, Q1, C7, C8, and C9 should be place 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 highcurrent 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 or input to avoid unwanted noise coupling. 6. 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. 7. C4 should be connected close to the RS1 and OS1 pins, while R2 should be connected close to the inductor. 8. R7 should be connected directly to the output pin of inductor L1 to sense precisely its DCR. 9. For good thermal coupling, a 4-layer PCB layout is recommended and PCB vias are required from the exposed pad (EP) for the TQFN45-24 paddle to the middle plans and bottom plane. The EP is internally connected to IN. 5.
2.
3.
4.
C3 0.1F D1 BAS16
2
1
U1 LX1 LX1 BST1 VL1 VL1 IN N/C EP COMP1 OUT2 N/C GND GND2 N/C LX1 LX1 DL FB1 RS1 OS1
24
L1 4.7H C10 2.2nF R5 150
VOUT1 3.3V/4.5A
2
23
5
20
R2 2k Q1
C4 220nF R6 open
R3 9.09k
J1
1
D1
18
16
VIN1 6.0V - 24.0V
19
13
AAT2688
22 3 14 15
R7 0
C7 22F C6 R1 150pF 3.92K R4 1.96k C5 2.2nF
C8 C9 22F 22F
C14 2.2F
3 2 1
4
N/C EN1 IN2 N/C EN2
11
6
12
VOUT2 1.8V/0.6A R8 open C12 2.2F C11 open
EN1 C1 220F 25V + C15 open C13 1F 25V
VIN2
10
17
9
7
C2 2.2F EN2
3 2 1 8 21
TQFN 45-24
U1 C1 C2, C12, C14 C3 C4 C5, C6, C10, C11 C7, C8, C9 C13 D1 Q1 L1 R1-R5
AAT2688 Analogic Technologies, Hi-Voltage Buck/LDO, TQFN45-24 Cap, MLC, 220F/25V, Electrolytic cap Cap, MLC, 2.2F, 6.3V, 0805 Cap, MLC, 0.1F/6.3V, 0603 Cap, MLC, 220nF/6.3V, 0402 Cap, MLC, misc, 0603 Cap, MLC, 22F/10V, 1206 Cap, MLC, 1F, 25V, 0805 BAS16, Generic, Rectifier, 0.2A/85V, Ultrafast, SOT23 SOP8 MOSFET, Si4686DY, Vishay or FDS8884, Fairchild RCH108NP-4R7M, Sumida, 4.7H, ISAT = 5.7A, DCR = 11.7m; Unshielded or Wurth 744 771 004, 4.7H, ISAT = 6.8A, DCR = 11m, Shielded Carbon film resistor, 0402
Figure 4: AAT2688 Evaluation Board Schematic for VIN = 6V-24V and VOUT = 3.3V.
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Figure 5: AAT2688IFK Evaluation Board Top Layer.
Figure 6: AAT2688IFK Evaluation Board Mid1 Layer.
Figure 7: AAT2688IFK Evaluation Board Mid2 Layer.
Figure 8: AAT2688IFK Evaluation Board Bottom Layer.
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
AAT2688 Design Example
Specifications
VO1 = 3.3V @ 4.5A, Pulsed Load ILOAD = 4.5A VO2 = 1.8V @ 600mA VIN1 = 12V FS = 490kHz TAMB = 85C in TQFN45-24 package
Channel 1 Output Inductor
For Sumida inductor RCH108NP-4R7M, 4.7H, DCR = 11.7m max.
I =
VOUT1 VOUT1 3.3V 3.3V * 1= * 1= 1A L1 * FS VIN1 4.7H * 490kHz 12V I = 4.5A + 1A = 5.5A 2
IPK1 = IOUT1 +
PL1 = IOUT12 * DCR = 5.5A2 * 11.7m = 354mW
Channel 1 Output Capacitor
VDROOP = 0.4V
COUT =
3 * ILOAD 3 * 4.5A = = 69F; use 3x22F 0.4V * 490kHz VDROOP * FS 1 2* 3
IRMS(MAX) =
*
VOUT1 * (VIN(MAX) - VOUT1) 1 3.3V * (24V - 3.3V) * = 357mARMS = L * FS * VIN1(MAX) 2 * 3 4.7H * 490kHz * 24V
PRMS = ESR * IRMS2 = 5m * (357mA)2 = 0.6W
Channel 1 Input Capacitor
Input Ripple VPP = 33mV
CIN1 =
1 = VPP - ESR * 4 * FS IOUT1
1 = 219F 33mV - 5m * 4 * 490kHz 4.5A
For low cost applications, a 220F/25V electrolytic capacitor in parallel with a 1F/25V ceramic capacitor is used to reduce the ESR.
IRMS =
IOUT1 = 2.25A 2
P = ESR * (IRMS)2 = 5m * (2.25A)2 = 25.3mW
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A 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 = 10m
IPRESET =
VS 100mV = = 10A > ILIMIT 10m DCR
R8 =
VOUT * R2 3.3V * 2k = 165k = 0.1V - 6A * 10m VS - ILIMIT * DCR R2 * R 8 2k * 165k = = 2k 165k - 2k R8 - R 2
R7 =
AAT2688 Losses
All values assume 25C ambient temperature and thermal resistor of 50C/W in the TQFN45-24 package.
PTOTAL = IOUT12 * RDS(ON)H * D + (tSW * FS * IOUT1 + IQ) * VIN + (VIN2 - VOUT2) * IOUT2
2 PTOTAL = 4.5A * 70m * 3.3V + (5ns * 490kHz * 4.5A + 70A) * 12V + (3.3 - 1.8) * 600mA 12V
PTOTAL = 1.42W TJ(MAX) = TAMB + JA * PLOSS = 85C + (33C/W) * 1.42W = 131C
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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Ordering Information
Voltage Package
TQFN45-24 Channel 1 Adjustable Channel 2 1.8
Marking1
3WXYY
Part Number (Tape and Reel)2
AAT2688IFK-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 Adjustable 1.8 Code A I
Package Information
TQFN45-243
Pin 1 Dot by Marking 4.000 0.050 0.400 0.050 2.800 0.050 Pin 1 Identification Chamfer 0.400 x 45
5.000 0.050
3.800 0.050
3.000 REF
0.750 0.050
0.203 REF 0.000 - 0.050
Side View
0.500 BSC 2.000 REF
0.250 0.050
Top View
All dimensions in millimeters.
Bottom View
1. XYY = Assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to 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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PRODUCT DATASHEET
AAT2688
SystemPowerTM 4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
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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