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PDF AAT3194 Data sheet ( Hoja de datos )
| Número de pieza | AAT3194 | |
| Descripción | High Efficiency 1.5X Fractional Charge Pump | |
| Fabricantes | AAT | |
| Logotipo |  |
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AAT3194
High Efficiency 1.5X Fractional Charge
Pump For White LED Applications
General Description
Features
ChargePump™
The AAT3194 is a low noise, constant frequency
charge pump DC/DC converters that use fractional
(1.5X) conversion to increase efficiency in white
LED applications. The devices can be used to pro-
duce current levels up to 20mA for each output
from a 2.7V to 5.5V input. A low external parts
count (two 1µF flying capacitors and two small
bypass capacitors at IN and OUT) makes these
devices ideally suited for small, battery-powered
applications.
AnalogicTech’s Simple Serial Control™ (S2Cwire™)
interface is used to enable, disable, and set the
LED drive current for 32-level logarithmic scale LED
brightness control. The AAT3194 has a thermal
management system for protection in the event of a
short-circuit condition on any of the output pins.
Built-in soft-start circuitry prevents excessive inrush
current during start-up. A high switching frequency
enables the use of small external capacitors. A low-
current shutdown feature disconnects the load from
VIN and reduces quiescent current to less than 1µA.
The AAT3194 is available in a Pb-free 12-pin
TSOPJW package.
• VIN Range: 2.7V to 5.5V
• 20mA Full-Scale Current
• Simple Serial Control (S2Cwire) Interface
— 32-Position Logarithmic Scale with Digital
Control
• Low Noise Constant Frequency Operation
• 33% Less Input Current Than Doubler
Charge Pump
• High Accuracy Brightness Matching
• Small Application Circuit
• Regulated Output Current
• Automatic Soft Start
• No Inductors
• 600kHz Switching Frequency
• IQ <1µA in Shutdown
• Temperature Range: -40°C to 85°C
• 12-Pin TSOPJW Package
Applications
• Programmable Current Source
• White LED Backlighting
Typical Application
VBATTERY
CIN COUT
1µF 1µF
EN/SET
IN C1+
OUT
C1-
C2+
AAT3194
C2-
EN/SET
D1
D2
D3
D4
GND
C1
1µF
C2
1µF
D4 D3 D2 D1
3194.2006.09.1.0
1
1 page  
AAT3194
High Efficiency 1.5X Fractional Charge
Pump For White LED Applications
Typical Characteristics
VIN = 3.5V, CIN = COUT = C1 = C2 = 1µF; TA = 25°C, unless otherwise noted.
Quiescent Current vs. Temperature
1.00
0.98
0.96
0.94
0.92
0.90
0.88
0.86
-40 -20 0 20 40 60 80 100
Temperature (°C)
Efficiency vs. Supply Voltage
100
30mA
95
90
85
40mA
80
75
70
65
60
3.0
3.2
20mA
60mA
80mA
3.4 3.6 3.8 4.0
Supply Voltage (V)
4.2
4.4
Quiescent Current vs. Supply Voltage
1.2
1.1
1.0
0.9
0.8
0.7
0.6
3.0
3.5 4.0
4.5 5.0
Supply Voltage (V)
5.5
Efficiency vs. Load Current
96
94
92
90
88
86
84
82
80
0
20 40 60
Load Current (mA)
80
Shutdown Current vs. Temperature
1.000
0.100
0.010
0.001
-40
-20
0 20 40 60
Temperature (°C)
80 100
3194.2006.09.1.0
Oscillator Frequency vs. Temperature
710
700
690
680
670
660
650
640
630
620
610
-40 -20 0 20 40 60 80 100
Temperature (°C)
5
5 Page 
AAT3194
High Efficiency 1.5X Fractional Charge
Pump For White LED Applications
current drops below 0.05mA or when the level of
the power supply of IN approaches OUT. Refer to
the Typical Characteristics section of this datasheet
for measured plots of efficiency versus input volt-
age and output load current for the given charge
pump output voltage options.
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the previ-
ous section only accounts for efficiency of the
charge pump section itself. Due to the unique cir-
cuit architecture and design of the AAT3194, it is
very difficult to measure efficiency in terms of a per-
cent value comparing input power over output
power. Since the device outputs are pure constant
current sources, it is difficult to measure the output
voltage for a given output (D1 to D4) to derive an
output power measurement. For any given appli-
cation, white LED forward voltage levels can differ,
yet the output drive current will be maintained as a
constant. This makes quantifying output power a
difficult task when taken in the context of comparing
to other white LED driver circuit topologies. A bet-
ter way to quantify total device efficiency is to
observe the total input power to the device for a
given LED current drive level. The best white LED
driver for a given application should be based on
trade-offs of size, external components count, relia-
bility, operating range, and total energy usage...not
just "% efficiency."
AAT3194 Input Power vs. LED Current
700
600 VIN = 3.6V
500
400
300
200
100
0
0 20 40 60 80
Output (LED) Current (mA)
100
Capacitor Selection
Careful selection of the four external capacitors
CIN, C1, C2, and COUT is important because they will
affect turn-on time, output ripple, and transient per-
3194.2006.09.1.0
formance. Optimum performance will be obtained
when low equivalent series resistance (ESR)
ceramic capacitors are used. In general, low ESR
may be defined as less than 100mΩ. A value of
1µF for all four capacitors is a good starting point
when choosing capacitors. If the LED current
sources are only programmed for minimal current
levels, then the capacitor size may be decreased.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3194. Ceramic capacitors offer many
advantages over their tantalum and aluminum elec-
trolytic counterparts. A ceramic capacitor typically
has very low ESR, is lowest cost, has a smaller
PCB footprint, and is non-polarized. Low ESR
ceramic capacitors help maximize charge pump
transient response. Since ceramic capacitors are
non-polarized, they are not prone to incorrect con-
nection damage.
Equivalent Series Resistance: ESR is an impor-
tant characteristic to consider when selecting a
capacitor. ESR is a resistance internal to a capac-
itor that is caused by the leads, internal connec-
tions, size or area, material composition, and ambi-
ent temperature. Capacitor ESR is typically meas-
ured in milliohms for ceramic capacitors and can
range to more than several ohms for tantalum or
aluminum electrolytic capacitors.
Ceramic Capacitor Materials: Ceramic capacitors
less than 0.1µF are typically made from NPO or
C0G materials. NPO and C0G materials generally
have tight tolerance and are very stable over tem-
perature. Larger capacitor values are usually com-
posed of X7R, X5R, Z5U, or Y5V dielectric materi-
als. Large ceramic capacitors (i.e., greater than
2.2µF) are often available in low-cost Y5V and Z5U
dielectrics, but capacitors greater than 1µF are not
typically required for AAT3194 applications.
Capacitor area is another contributor to ESR.
Capacitors that are physically large will have a lower
ESR when compared to an equivalent material
smaller capacitor. These larger devices can improve
circuit transient response when compared to an
equal value capacitor in a smaller package size.
11
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| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet AAT3194.PDF ] | |
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