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AAT3172 Schematic ( PDF Datasheet ) - ANALOGICTECH

Teilenummer AAT3172
Beschreibung High Current LED Flash Driver Charge Pump IC
Hersteller ANALOGICTECH
Logo ANALOGICTECH Logo 




Gesamt 14 Seiten
AAT3172 Datasheet, Funktion
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AAT3172
High Current LED Flash Driver Charge Pump IC
General Description
The AAT3172 is a high output current, high effi-
ciency, low noise, low profile charge pump DC/DC
converter, ideal for multi-function LED photo-flash
applications where solution cost, size, and efficien-
cy are critical.
The dual charge pump in the AAT3172 is capable
of delivering 600mA peak output current. Two cur-
rent-controlled paths are available for users of dual
flash LEDs that prefer current matching. Each LED
channel can be easily programmed in 32 steps with
a single GPIO output through the AS2Cwire™
(Advanced Simple Serial Control™) interface. This
allows smooth transitions and flexible adjustment
of brightness in flash or other lighting modes.
The tri-mode (1X/1.5X/2X) operation of the internal
charge pump offers excellent power efficiency for
both flash and movie modes. Combined with a low
external parts count (two 1µF flying capacitors and
one small bypass capacitor at VIN and OUT), the
AAT3172 is ideally suited for small, battery-powered
applications.
The AAT3172 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
prevents excessive inrush current during start-up.
The shutdown feature disconnects the load from VIN
and reduces quiescent current to less than 1.0µA.
The AAT3172 is available in the Pb-free, thermally-
enhanced, 12-pin 3x3 TDFN package.
Features
ChargePump
• VIN Range: 2.7V to 5.5V
• 600mA Peak Output Current
• Tri-Mode 1X/1.5X/2X in Current Mode
• Voltage Mode Operation: 1.5X, 100mA
• Dual Regulated Current Sinks
• Current Match Between Current Sinks
• 32 Current Steps Set by AS2Cwire
• 1µF Input, Output, and Flying Capacitors
• <1.0µA of Shutdown
• Small Application Circuit
• No Inductors
• Automatic Soft Start
• 12-Pin TDFN 3x3 Package
• -40°C to +85°C Temperature Range
Applications
• Camera Phones
• Digital Still Cameras (DSCs)
• PDAs and Notebook PCs
• Smart Phones
Typical Application
2.7V to 5.5V
EN/SET
C1 C2
1µF 1µF
C1+ C1- C2+ C2-
VIN VOUT
CIN
4.7µF
AAT3172
COUT
2.2µF
Flash
LED 1
Flash
LED 2
EN/SET
GND
F1
F2
3172.2005.11.1.1
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AAT3172 Datasheet, Funktion
AAT3172
High Current LED Flash Driver Charge Pump IC
Typical Characteristics
VIN = 3.6V, CIN = 4.7µF, COUT = 2.2µF, C1 = C2 = 1µF, TA = 25°C, unless otherwise noted.
Load Characteristic
(VIN = 3.0V; 1.5X Mode; 50mA/ch Load)
Load Characteristic
(VIN = 3.6V; 1.5X Mode; 152mA/ch Load)
VIN
(100mV/div)
VOUT
(200mV/div)
VSINK
(200mV/div)
VIN
(100mV/div)
VOUT
(200mV/div)
VSINK
(200mV/div)
2µs/div
2µs/div
Load Characteristic
(VIN = 2.8V; 2X Mode; 152mA/ch Load)
VIN
(100mV/div)
VOUT
(200mV/div)
VSINK
(200mV/div)
2µs/div
Voltage Mode Load Regulation
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.1
0
VIN = 4.2V
VIN = 3.7V
VIN = 3.3V
15 30 45 60 75 90 105 120 135 150
Load Current (mA)
Voltage Mode Line Regulation
4.8
4.7
4.6 IOUT = 10mA
4.5
4.4 IOUT = 120mA
4.3 IOUT = 80mA
4.2 IOUT = 30mA
4.1
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
Input Voltage (V)
Voltage Mode Load Response
(VIN = 3.7V)
VOUT
(100mV/div)
IOUT
(100mA/div)
100mA
10mA
4.51V
5ms/div
6 3172.2005.11.1.1

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AAT3172 pdf, datenblatt
2.7V to 5.5V
EN/SET
AAT3172
High Current LED Flash Driver Charge Pump IC
C1 C2
1µF 1µF
C1+ C1- C2+ C2-
VIN VOUT
CIN
4.7µF
AAT 3172
EN/SET
GND
F1
F2
COUT
2.2µF
Flash
LED
STAT1
STAT2
Figure 2: Flash Plus Status Lighting.
LED Selection
The AAT3172 is designed to drive high intensity
white flash LEDs with forward voltages up to 4.4V.
Charge Pump Efficiency
η
=
POUT
PIN
=
100%
×
VF
VIN
1X Mode
=
100%
×
VF
1.5VIN
1.5X Mode
=
100%
×
VF
2VIN
2X Mode
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
performance. Optimum performance will be
obtained when low equivalent series resistance
(ESR) (<100m) ceramic capacitors are used. A
value of 1µF for all four capacitors is a good start-
ing point when choosing capacitors. If the LED cur-
rent sinks are only programmed for light current
levels, then the capacitor size may be decreased.
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3172. 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.
Equivalent Series Resistance
ESR is an important characteristic to consider
when selecting a capacitor. ESR is a resistance
internal to a capacitor that is caused by the leads,
internal connections, size or area, material compo-
sition, and ambient temperature. Capacitor ESR is
typically measured in milliohms for ceramic capac-
itors and can range to more than several ohms for
tantalum or aluminum electrolytic capacitors.
12 3172.2005.11.1.1

12 Page





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