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PDF AAT2688 Data sheet ( Hoja de datos )
| Número de pieza | AAT2688 | |
| Descripción | 4.5A PMIC Solution | |
| Fabricantes | Advanced Analogic Technologies | |
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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-on-
a-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 cur-
rent. 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 out-
put noise, low quiescent current, and excellent transient
response.
The step-down regulator includes integrated over-cur-
rent, soft-start and over-temperature protection. Inde-
pendent 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 -40°C to 85°C.
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 <35μA
• Independent Enable Pins
• Over-Current and Over-Temperature Protection
• Internal Soft Start
• 4x5mm 24-Pin TQFN Low Profile Package
• -40°C to 85°C Temperature Range
Applications
• DSL and Cable Modems
• Notebook Computers
• Satellite Set-top Boxes
• Wireless LAN Systems
Typical Application
C3
0.1μF
D1
BAS16
J1 2
1
VIN1
6.0V -24.0V
C14
2.2μF
+ C1
220μF
25V
VIN2
C13
1μF
25V
C2
2.2μF
L1 4.7μH/5.3A
LX1
BST1 DL
VL1 RS1
OS1
IN1 FB1
Q1 C10
R2 C4
2.2nF
2K 220nF
R5
150
COMP1
AAT2688
R1
3.92k
C5
2.2nF
EN1
IN2 OUT2
C6
150pF
VOUT2
EN2 GND
C12
2.2μF
TQFN45-24
VOUT1
3.3V/4.5A
R3
9.09k
C7 C8
22μF 22μF
C9
22μF
R4
1.96k
2688.2008.06.1.0
www.DataSheet.in
www.analogictech.com
1
1 page  
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 = 4.7µH)
100
90
80
70
60
50
40
30
20
10
0
0.1
1
VIN1 = 6V
VIN1 = 8V
VIN1 = 12V
VIN1 = 18V
VIN1 = 24V
10
100
1000
10000
Output Current (mA)
Step-Down Converter DC Regulation
(VOUT1 = 3.3V; L = 4.7µH)
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
0.1
VIN1 = 6V
VIN1 = 8V
VIN1 = 12V
VIN1 = 18V
VIN1 = 24V
1
10 100 1000
Output Current (mA)
10000
Step-Down Converter Output Voltage
Error vs. Input Voltage
(VOUT1 = 3.3V; L = 4.7µH)
2
IOUT1 = 0.10mA
IOUT1 = 100mA
1
IOUT1 = 1000mA
IOUT1 = 2250mA
IOUT1 = 3500mA
IOUT1 = 4500mA
0
-1
-2
68
10 12 14 16 18 20 22 24
Input Voltage (V)
Step-Down Converter Switching
Frequency vs. Temperature
(VIN1 = 12V; VOUT1 = 3.3V; IOUT1 = 4.5A)
510
500
490
480
470
-40
-15 10 35 60
Temperature (°C)
85
Step-Down Converter Switching Frequency
vs. Input Voltage
(VOUT1 = 3.3V; IOUT1 = 4.5A)
3
2
1
0
-1
-2
-3
6 8 10 12 14 16 18 20 22 24
Input Voltage (V)
No Load Step-Down Converter Input Current
vs. Input Voltage
(VEN1 = VIN1)
0.70
0.65
0.60
0.55
0.50
0.45
0.40 85°C
0.35 25°C
-40°C
0.30
Input Voltage (V)
2688.2008.06.1.0
www.DataSheet.in
www.analogictech.com
5
5 Page 
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 inte-
grated 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 fre-
quency (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 option-
al 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 regu-
lator providing 1.8V with up to 600mA output current.
The input voltage range is 2.7V to 5.5V. The LDO pro-
vides very low noise output which can be derived direct-
ly from Output 1.
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 max-
imum duty cycle is 85%. Example: with R4 = 1.96KΩ,
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 (kΩ)
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).
Channel 1 Regulator
Output Capacitor Selection
Three 22μF 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 4.7μH 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 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 select-
ed 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 synchro-
nous 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.
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.
2688.2008.06.1.0
www.analogictech.com
11
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