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AAT2687 Schematic ( PDF Datasheet ) - Advanced Analogic Technologies

Teilenummer AAT2687
Beschreibung PMIC Solution
Hersteller Advanced Analogic Technologies
Logo Advanced Analogic Technologies Logo 




Gesamt 20 Seiten
AAT2687 Datasheet, Funktion
SystemPowerTM
PRODUCT DATASHEET
AAT2687
PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters
General Description
The AAT2687 provides two independently regulated DC
outputs; consisting of a high voltage step-down regula-
tor 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.
Channel 1 is a step-down 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 filter-
ing 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 over-
current protection, soft-start and over-temperature dis-
able features. Independent input and enable pins pro-
vide maximum design flexibility.
The AAT2687 is available in the Pb-free, 4x5mm 24-pin
TQFN package. The rated operating temperature range is
-40°C to 85°C.
Features
• 2-Output Step-Down Converters:
Channel 1 Step-Down: VIN1 = 6V to 24V
VOUT1 Adjustable from 1.5V to 5.5V
IOUT1 up to 4.5A
• 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
• Programmable Over-Current Protection
• Over-Temperature Protection
• Internal Soft Start
• 4x5mm 24-Pin TQFN Low Profile Thermally Enhanced
Package
• -40°C to 85°C Temperature Range
Applications
• DSL and Cable Modems
• Notebook Computers
• Satellite Settop Box
• Wireless LAN Systems
Typical Application
VIN1
6.0V - 24.0V
J1
2
1
C3
0.1µF
D1
BAS16
C14
2.2µF
+ C1
220µF
25V
VIN2
C13
1µF
25V
C2
2.2µF
LX1
BST
VL1 RS1
OS1
IN1 FB1
L1
4.7µH 5.3A
D2
R2 C4
2k 220nF
C10
2.2nF
R5
450
VOUT1
3.3V/4.5A
R3
8.87k
C7 C8 C9
22µF 22µF 22µF
COMP1
AAT2687
EN1
OUT2
IN2
EN2 GND
TQFN45-24
R1 C5
3.92K 2.2nF
C6
VOUT2 150pF
1.8V/600mA
R4
1.96k
C12
2.2µF
2687.2008.06.1.0
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1






AAT2687 Datasheet, Funktion
SystemPowerTM
PRODUCT DATASHEET
AAT2687
PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters
Typical Characteristics—Channel 1
Step-Down Converter Load Transient
(VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH)
4.05
16
3.80
14
3.55
12
3.30
10
3.05
8
2.80
2.55
4.5A
6
4
2.30
2.05
450mA
2
0
Time (100µs/div)
Step-Down Converter Load Transient
(VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH)
3.7 16
3.5 14
3.3 12
3.1 10
2.9 8
2.7 6
2.5
4.5A
4
2.3
2.25A
2
2.1 0
Time (100µs/div)
Step-Down Converter Load Transient
(VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH)
3.5 10
3.4 9
3.3 8
3.2 7
3.1 6
35
4.5A
2.9 4
2.8
3.375A
3
2.7 2
Time (100µs/div)
Step-Down Converter Line Transient
(VOUT1 = 3.3V; COUT1 = 66µF; L = 4.7µH)
3.36
22
3.34
20
3.32
18
3.3 16
3.28
14
3.26
12
3.24
10
3.22
8
3.2 6
Time (100µs/div)
Step-Down Converter Output Voltage Ripple
(VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH; IOUT1 = 4.5A)
3.34
35
3.32
30
3.3 25
3.28
20
3.26
15
3.24
10
3.22
5
3.2 0
3.18
-5
Time (1µs/div)
Step-Down Converter Output Voltage Ripple
(VOUT1 = 3.3V; VIN1 = 12V; COUT1 = 66µF; L = 4.7µH; IOUT1 = 1mA)
3.36
35
3.34
30
3.32
25
3.3 20
3.28
15
3.26
10
3.24
5
3.22
0
3.2 -5
Time (2µs/div)
6
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2687.2008.06.1.0

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AAT2687 pdf, datenblatt
SystemPowerTM
PRODUCT DATASHEET
AAT2687
PMIC Solution for 24V Systems with 2 High Performance Step-Down Converters
Over-Current Protection
The output 1 controller provides true-load DC output cur-
rent sensing which protects the load and limits compo-
nent stresses. The output current is sensed through the
DC resistance in the output inductor (DCR). The control-
ler reduces the operating frequency when an over-current
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).
V OUT1
L1 3.3V/4.5A
LX1
4.7μH
R2
2k
RS1
OS1
C4
220nF
R7
R8
Figure 2: Optional Resistor Network to Adjust the
Current Limit Less than the Pre-Set Over-Current
Threshold (Add R7 and R8).
VOUT1
L1 3.3V/4.5A
LX1
4.7μH
R2 C4
2k 220nF
RS1 R6
R7
OS1
Figure 3: Optional Resistor Network to Adjust the
Current Limit Greater than the Pre-Set Over-
Current Level (Add R6 and 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
AAT2687 is physically located more than three centime-
ters 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 maximiz-
ing 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 regu-
lator output operation, ceramic capacitors are recom-
mended for CIN due to their inherent capability over
tantalum capacitors to withstand input current surges
from low impedance sources, such as batteries in por-
table devices.
Channel 2 Output Capacitor
For proper load voltage regulation and operational stabil-
ity, 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 AAT2687 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 cur-
rent conditions range from 1μF to 10μF. Applications
utilizing the exceptionally low output noise and optimum
power supply ripple rejection characteristics of the chan-
nel 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 Enable Function
The AAT2687 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 con-
tinuously on state. When the LDO regulator is in shut-
12
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