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PDF AAT3174 Data sheet ( Hoja de datos )
| Número de pieza | AAT3174 | |
| Descripción | High Current LED Flash Driver Charge Pump IC | |
| Fabricantes | ANALOGICTECH | |
| Logotipo |  |
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AAT3174
High Current, High Efficiency Charge Pump
General Description
Features
ChargePump™
The AAT3174 is a high output current, high effi-
ciency, low noise, low profile charge pump DC/DC
converter. The device is ideal for multi-functional
LED photo-flash applications where solution cost,
size, and efficiency are critical.
The AAT3174 is capable of driving a regulated out-
put current up to 800mA. Output current levels can
be easily programmed in 16 steps through
AnalogicTech's Simple Serial Control™ (S2Cwire™)
interface controlled by a single microcontroller
GPIO line. This allows smooth transitions and flexi-
ble adjustment of brightness in flash or other light-
ing modes. The maximum output current can also
be set with an external RSET resistor.
The tri-mode (1X/1.5X/2X) operation of the internal
charge pump offers excellent power efficiency
throughout the output current range for both flash
and movie modes. Combined with a low external
parts count (two 1µF flying capacitors and two
small bypass capacitors at VIN and OUT), the
AAT3174 is ideally suited for small battery-pow-
ered applications.
The AAT3174 has a thermal management system to
protect the device in the event of a short-circuit con-
dition at the output pin. Built-in soft-start circuitry pre-
vents excessive inrush current during start-up. The
shutdown feature disconnects the load from VIN and
reduces quiescent current to less than 1µA.
The AAT3174 is available in a Pb-free, thermally-
enhanced 12-pin 3x3mm TDFN package and is spec-
ified over the -40°C to +85°C temperature range.
• Up to 800mA Output Current
• Tri-Mode 1X/1.5X/2X in Current Mode
• 16 Current Steps Set by S2Cwire
• External RSET to Set Maximum Current
• <1µA of Shutdown
• Small Application Circuit
• No Inductors
• Automatic Soft Start
• 12-Pin TDFN 3x3mm Package
• -40°C to +85°C Temperature Range
Applications
• Camcorders
• Camera Phones
• Digital Still Cameras
• PDAs and Notebook PCs
• Smart Phones
Typical Application
C1 C2
1µF 1µF
VIN
(2.7V to 5.5V)
Enable or
S2Cwire
C1+ C1- C2+ C2-
C IN
4.7µF
VIN
OUT
AAT3174
EN/SET
RSET
GND
FL
COUT
2.2µF
Flash
LED
3174.2006.05.1.2
1
1 page  
AAT3174
High Current, High Efficiency Charge Pump
Typical Characteristics
VIN = 3.6V, CIN = 4.7µF, COUT = 2.2µF, C1 = C2 = 1µF, TA = 25°C, unless otherwise noted.
Efficiency vs. Supply Voltage
100
90
80
70
60 ILED = 300mA
50 ILED = 150mA
40
30
20
10
0
2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
Supply Voltage (V)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(200mA/div)
Turn-On to 1X Mode
(VIN = 4.2V; ILED = 150mA)
Time (200µs/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(200mA/div)
Turn-On to 1.5X Mode
(VIN = 3.2V; ILED = 150mA)
Time (200µs/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(500mA/div)
Turn-On to 1X Mode
(VIN = 4.2V; ILED = 600mA)
Time (200µs/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(500mA/div)
Turn-On to 2X Mode
(VIN = 3.2V; ILED = 600mA)
Time (200µs/div)
EN
(2V/div)
VF
(1V/div)
IIN
(200mA/div)
Turn-Off from 1.5X Mode
(VIN = 3.2V; ILED = 150mA)
Time (200µs/div)
3174.2006.05.1.2
5
5 Page 
AAT3174
High Current, High Efficiency Charge Pump
For examples of standard 1% values where the
LED flash current level is targeted for 700mA, see
Table 3.
R1
(kΩ)
920
732
649
562
R2
(kΩ)
193
205
210
223
ILED
Torch (mA)
122
153
173
200
ILED
Flash (mA)
703
701
707
703
Table 3: Open-Drain I/O Example
Resistor Values.
If the I/O port must be configured as an open-drain
PMOS type output, the appropriate equations can
be generated from these same concepts. As done
in the previous example, the necessary values can
then be calculated.
As a reference, the equations applicable to the
PMOS case are:
600mA · 187kΩ
R1 = ILED (flash)
VIO
0.7
-
1
R2
=
1
R1
-
ILED (torch)
600mA · 187kΩ
The value to use for VIO must come from the I/O
supply voltage used in the system. 0.7V is the typ-
ical value of the VRSET parameter found in the
Electrical Characteristics.
For a push-pull I/O port output configuration, first
calculate the overall RSET value needed for the
desired flash level LED current:
RSET
=
600mA · 187kΩ
ILED (flash)
Next, choose a reasonable value for R1. A value
that is slightly larger than RSET, calculated from
above, is appropriate. Calculate R2 and then calcu-
late the torch mode current level that results:
R2
=
RSET · R1
R1 - RSET
ILED (torch) = 600mA · 187kΩ ·
⎛ R2 - R1
⎝ R1 · R2
-
VIO ⎞
0.7V · R2⎠
Once again, the current and resistance values used
in the equations come from the conditions placed on
the IDX parameter of the Electrical Characteristics
table. 0.7V is the typical value for the VRSET param-
eter. The value to use for VIO must come from the
I/O supply voltage used in the system.
Example standard 1% values are provided in Table 4.
R1
(kΩ)
169
165
162
160
R2
(kΩ)
1000
1000
1000
1000
ILED
Torch (mA)
95
111
124
132
ILED
Flash (mA)
776
792
805
813
Table 4: Push-Pull I/O Example
Resistor Values.
In all of the approaches mentioned, the open-drain
NMOS or PMOS type configurations offer the most
flexibility for current level selection.
When configured as an output, if the I/O port is only
push-pull type, then the equivalent open-drain
NMOS can also be realized. To realize this, acti-
vate the port as output only when driving the line
low. Otherwise, to release the line, set the port to
be tri-stated.
3174.2006.05.1.2
11
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