Analogic AAT3170 High current led flash driver charge pump ic Datasheet

PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
General Description
Features
The AAT3170 is a high output current, high efficiency,
low noise, low profile charge pump DC/DC converter,
ideal for multi-function LED photo-flash applications
where solution cost, size, and efficiency are critical.
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The dual charge pump in the AAT3170 is capable of
delivering 600mA output current. Two current-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 AAT3170 is ideally
suited for small, battery-powered applications.
VIN Range: 2.7V to 5.5V
600mA Output Current
Tri-Mode 1X/1.5X/2X in Current Mode
Voltage Mode Operation: 1.5X, 200mA
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 3x3mm Package
-40°C to +85°C Temperature Range
Applications
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The AAT3170 has a thermal management system to protect the device in the event of a short-circuit condition 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.
Camera Phones
Digital Still Cameras (DSCs)
PDAs and Notebook PCs
Smart Phones
The AAT3170 is available in the Pb-free, thermallyenhanced, 12-pin 3x3mm TDFN package.
Typical Application
C1
1μF
C1+
2.7V to 5.5V
C2
1μF
C1-
C2+
VIN
C IN
4.7μF
C2-
VOUT
C OUT
2.2μF
AAT3170
Flash
LED 1
Flash
LED 2
EN/SET
EN/SET
F1
CT
CT
0.1μF
3170.2007.11.1.2
F2
GND
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1
PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Pin Descriptions
Pin #
Symbol
1, 12
2
3
4
5
6
7
VIN
C1+
C1GND
F1
F2
EN/SET
8
CT
9
10
11
EP
C2C2+
VOUT
Function
Input power supply pin. Requires 4.7μF or larger ceramic bypass capacitor to ground.
Flying capacitor C1 positive terminal. Connect a 1μF ceramic capacitor between C1+ and C1-.
Flying capacitor C1 negative terminal.
Ground connection.
Current sink input #1.
Current sink input #2.
AS2Cwire serial interface control pin.
Flash timer control capacitor input. Connect a 100nF capacitor from CT to GND for a one second timeout
duration.
Flying capacitor C2 negative terminal.
Flying capacitor C2 positive terminal. Connect a 1μF ceramic capacitor between C2+ and C2-.
Charge pump output. Requires 2.2μF or larger ceramic capacitor connected between this pin and ground.
Exposed paddle (bottom); connect to GND directly beneath package.
Pin Configuration
TDFN33-12
(Top View)
VIN
C1+
C1GND
F1
F2
2
1
12
2
11
3
10
4
9
5
8
6
7
VIN
VOUT
C2+
C2CT
EN/SET
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3170.2007.11.1.2
PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted.
Symbol
VIN
VEN
VEN(MAX)
IOUT
TJ
TS
TLEAD
Description
Input Voltage
EN to GND Voltage
Maximum EN to Input Voltage
Maximum DC Output Current
Operating Junction Temperature Range
Storage Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
-0.3 to 6.0
VIN + 0.3
700
-40 to 150
-65 to 150
300
V
V
V
mA
°C
°C
°C
Value
Units
50
2
°C/W
W
Thermal Information2, 3
Symbol
θJA
PD
Description
Maximum Thermal Resistance
Maximum Power Dissipation
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
3. Derate 20mW/°C above 40°C ambient temperature.
3170.2007.11.1.2
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PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Electrical Characteristics1
CIN = 4.7μF, COUT = 2.2μF, C1 = C2 = 1.0μF; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C,
VIN = 3.6V.
Symbol
Description
Conditions
Power Supply
Input Voltage Range
VIN
ICC
ISHDN(MAX)
IOUT(MAX)
I(D-Match)
I(D-Match)
IDX
FCLK
VREG
TSS
EN/SET
VIL
VIH
TEN/SET LO
TEN/SET HI MIN
TEN/SET HI MAX
TOFF
TLAT
Input Current
Operating Current
VIN Pin Shutdown Current
Maximum Output Current
Current Matching Between
Outputs; High Current
Current Matching Between
Outputs; Low Current
Output Current Accuracy
Clock Frequency
Voltage Mode Regulation
Soft-Start Time
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
Minimum EN/SET High Time
Maximum EN/SET High Time
EN/SET Off Timeout
EN/SET Latch Timeout
EN/SET Input Leakage
Min
Typ
2.7
ON/OFF Standby Mode, Code Address = 4, Data = 2
1X, No Load Current
3.0 ≤ VIN ≤ 5.5, 1.5X Mode, No Load Current
3.0 ≤ VIN ≤ 5.5, 2X Mode, No Load Current
EN = 0
VF = 3.6V
VIN = 3.6V, TA = 25°C, 428mA; Code Address = 3,
Data = 2; Code Address = 0, Data = 4
VIN = 3.6V, TA = 25°C, 100mA; Code Address = 3,
Data =1; Code Address = 0, Data = 1
TA = 25°C, Code 1, HI Scale
EN/SET Code Address = 6, Data = 2
VIN = 2.7V
VIN = 5.5V
10
300
2.0
3.0
Units
5.5
V
μA
4.0
6.0
1.0
μA
mA
8
%
8
%
330
1
4.5
200
4.9
0.4
1.4
0.3
75
50
-1
mA
600
270
4.1
Max
75
500
500
1
mA
MHz
V
μs
V
V
μs
ns
μs
μs
μs
μA
1. The AAT3170 is guaranteed to meet performance specifications from 0°C to 70°C. Specification over the -40°C to +85°C operating temperature range is assured by design,
characterization, and correlation with statistical process controls.
4
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3170.2007.11.1.2
PRODUCT DATASHEET
AAT3170
ChargePumpTM
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.
Efficiency vs. Supply Voltage
Turn-On to 1X Mode
(VIN = 4.2V; 50mA/ch Load)
100
Efficiency (%)
90
50mA/ch
VF = 2.9V
80
70
EN
(2V/div)
152mA/ch
VF = 3.2V
60
VOUT
(2V/div)
VSINK
(1V/div)
50
95mA/ch
VF = 3.1V
40
30
IIN
(200mA/div)
20
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
Time (200µs/div)
Supply Voltage (V)
Turn-On to 1.5X Mode
Turn-On to 1X Mode
(VIN = 3.2V; 50mA/ch Load)
(VIN = 4.2V; 300mA/ch Load)
EN
(2V/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(200mA/div)
IIN
(500mA/div)
Time (200µs/div)
Time (500µs/div)
Turn-On to 2X Mode
Turn-Off from 1.5X Mode
(VIN = 3.2V; 300mA/ch Load)
(VIN = 3.2V; 50mA/ch Load)
EN
(2V/div)
EN
(2V/div)
VOUT
(2V/div)
VSINK
(1V/div)
VF
(1V/div)
IIN
(500mA/div)
IIN
(200mA/div)
Time (500µs/div)
3170.2007.11.1.2
Time (200µs/div)
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PRODUCT DATASHEET
AAT3170
ChargePumpTM
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
Load Characteristic
(VIN = 3.0V; 1.5X Mode; 50mA/ch Load)
(VIN = 3.6V; 1.5X Mode; 152mA/ch Load)
VIN
(100mV/div)
VIN
(100mV/div)
VOUT
(200mV/div)
VOUT
(200mV/div)
VSINK
(200mV/div)
VSINK
(200mV/div)
Time (2µs/div)
Time (2µs/div)
Load Characteristic
Voltage Mode Line Regulation
(VIN = 2.8V; 2X Mode; 152mA/ch Load)
4.8
Output Voltage (V)
VIN
(100mV/div)
VOUT
(200mV/div)
VSINK
(200mV/div)
4.7
IOUT = 10mA
4.6
4.5
4.4
IOUT = 80mA
4.3
IOUT = 30mA
IOUT = 120mA
4.2
4.1
4.0
Time (2µs/div)
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)
Voltage Mode Load Regulation
Flash Timer Duration
1.8
4.7
1.6
4.6
VIN = 4.2V
4.5
VIN = 3.7V
4.4
VIN = 3.3V
4.3
4.2
0
50
100
150
200
250
Flash Time (s)
Output Voltage (V)
(CT = 0.1µF; Data = 1)
4.8
1.2
0.8
-40°C
0.4
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Supply Voltage (V)
Load Current (mA)
6
25°C
1.0
0.6
300
85°C
1.4
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3170.2007.11.1.2
PRODUCT DATASHEET
AAT3170
ChargePumpTM
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.
Flash Timer Duration
EN/SET Latch Timeout vs. Supply Voltage
(CT = 0.1µF; Data = 16)
EN/SET Latch Timeout (µs)
Flash Time (ms)
140
120
85°C
100
80
25°C
60
-40°C
40
20
350
300
250
200
50
0
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Supply Voltage (V)
EN/SET Off Timeout vs. Supply Voltage
EN/SET High Threshold Voltage
vs. Supply Voltage and Temperature
300
-40°C
25°C
200
150
85°C
100
50
0
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
EN/SET High Threshold Voltage (V)
EN/SET Off Timeout (µs)
85°C
100
Supply Voltage (V)
350
1.0
0.9
-40°C
0.8
0.7
0.6
25°C
85°C
0.5
0.4
Supply Voltage (V)
EN/SET Low Threshold Voltage (V)
25°C
150
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
250
-40°C
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Supply Voltage (V)
EN/SET Low Threshold Voltage
vs. Supply Voltage and Temperature
1.0
0.9
-40°C
0.8
0.7
0.6
25°C
85°C
0.5
0.4
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Supply Voltage (V)
3170.2007.11.1.2
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PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Functional Block Diagram
C1+
C1-
C2+
C2-
VIN
Charge Pump
Section 1
Charge Pump
Section 2
OUT
1MHz
Oscillator
Soft Start
Control
F1
EN/SET
System Control;
AS 2Cwire;
Timing
F2
GND
CT
Functional Description
The AAT3170 is a high efficiency, low noise, dual stage
tri-mode 1X/1.5X/2X charge pump device intended for
photo-flash LED applications. The AAT3170 requires
only four external components: two 1.0μF ceramic
capacitors for the charge pump flying capacitors, one
4.7μF ceramic capacitor for CIN, and one 2.2μF ceramic
capacitor for COUT.
The charge pump is designed to deliver load currents up
to 600mA. The dual stage charge pump section contains
soft-start circuitry to prevent excessive in-rush current
during start-up. System efficiency is maximized with a
tri-mode, dual stage charge pump topology. The internal
clock oscillator, which operates at 1MHz, allows the use
of small external components.
The tri-mode charge pump architecture optimizes power
conversion efficiency. Depending upon the combination
of load current, input voltage, and nominal LED forward
voltage, the charge pump will operate in a 1X, 1.5X, or
2X mode to generate the output voltage required to
power the load for a programmed constant current setting. This results in significant power savings over volt-
8
age doubling architectures, especially when the LEDs are
continuously operated at lower current levels in movie
viewing or flashlight modes.
Constant Current Channels
The AAT3170 contains two programmable constant current sinks for integrated flash circuit control. Efficiency is
optimized with the low dropout characteristic of the current sinks. The low dropout performance extends the
battery operating range for 1X and 1.5X modes, improving efficiency and extending battery life. Each constant
current sink is programmable through the AS2Cwire
serial interface. Independent current settings can be
used for a multistage flash LED control. This feature
allows users to conveniently drive separate dual flash
LEDs directly while achieving good brightness matching.
Also, F1 and F2 can be connected together for single
output configuration.
Modes of Operation
In addition to the data registers that set the current levels for the two current sinks, the AAT3170 has three
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3170.2007.11.1.2
PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
mode registers. Register 3 is the HI/LO mode register.
It sets the maximum per channel current level to either
300mA or 50mA. Each channel can be set independently so one channel can be for flash while the other
can be in a low constant current mode.
Register 4 is the ON/OFF register. When set with Data
= 1, both current sources are enabled (default); when
set with Data = 2, both current sources are disabled.
When Register 4 is set to OFF, the device is in standby
mode with significantly reduced quiescent current.
The AAT3170 has a software programmable timer function to automatically adjust the flash on-time duration.
This feature can be used directly to set the flash ontime, or it can be used indirectly for fault tolerant flash
protection. When used for flash protection, the user can
be sure that the flash will still turn off in the event of any
system software or hardware malfunction.
Write to Address 5 to enable the flash timer and flash
channels. When the timer register is addressed and data
is latched, the ON/OFF register is automatically switched
to ON, enabling the current sinks for the duration of the
programmed time. When the timer expires, the ON/OFF
register is switched to OFF, disabling the current sinks.
The on-time T depends on the combination of the setting
of the timer register and the value of the timing capacitor, which are listed in the “Timer Register” table.
Calculate the timer capacitor value according to the following formula:
T (seconds) = 10 · CT (μF)
where CT is in micro-farads.
For example, using a 0.1μF timer capacitor value results
in an on-time duration of one second.
The AAT3170 also includes a regulated output voltage
mode setting. By setting Register 6 with Data = 2 for
voltage mode, the charge pump delivers a regulated
4.5V output that continuously operates in 1.5X mode. It
is suitable for driving loads of up to 200mA. The voltage
mode may be used to drive LEDs with ballast resistors.
Driving either F1 or F2 in current mode will override the
voltage mode state until F1 and F2 are set back to zero
current by either data or mode register. Setting Register
5 with Data = 1 will reset the mode back to current
mode and the charge pump output voltage will regulate
appropriately.
3170.2007.11.1.2
AS2Cwire Serial Interface
The AAT3170 utilizes the AS2Cwire serial interface to
enable/disable the charge pump, set the operating
mode, and adjust the output current level of each constant current sink. Each current sink can be independently programmed with sixteen current levels (see
table below). AS2Cwire incorporates addressing to program the operating modes and current level settings.
Constant Current Sink
Nominal Programming Levels
Data
300mA HI Scale
ISINK (mA/chnl)
50mA LO Scale
ISINK (mA/chnl)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
300
267
238
214
190
167
152
133
119
105
95
86
76
67
62
0
50
44
40
36
32
28
25
22
20
17
16
14
13
11
10
0
AS2Cwire relies on the number of rising edges of the EN/
SET pin to address and load the registers. AS2Cwire
latches data or address after the EN/SET pin has been
held high for time TLAT (500μs). Address or data is differentiated by the number of EN/SET rising edges.
Since the data registers are 4 bits each, the differentiating number of pulses is 24 or 16, so that Address 0 is
signified by 17 rising edges, Address 1 by 18 rising
edges, and so forth. Data is set to any number of rising
edges between 1 and including 16. A typical write protocol is a burst of EN/SET rising edges, signifying a particular address, followed by a pause with EN/SET held
high for the TLAT timeout period, a burst of rising edges
signifying data, and a TLAT timeout for the data registers.
Once an address is set, then multiple writes to that
address are allowed where only data is issued.
When EN/SET is held low for an amount of time greater
than TOFF (500μs), the AAT3170 enters into shutdown
mode and draws less than 1μA from the supply. Address
0 is the default address on the first rising edge after the
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PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Timer Register (Address 5)
AAT3170 has been disabled. After shutdown, if only data
is issued with the first rising edge (i.e., 1 - 16 edges, no
address given), both current sinks will be programmed
since the default will be Address 0.
Data
On-Time
T (sec) = 10 · CT (μF)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
16/16 x T
15/16 x T
14/16 x T
13/16 x T
12/16 x T
11/16 x T
10/16 x T
9/16 x T
8/16 x T
7/16 x T
6/16 x T
5/16 x T
4/16 x T
3/16 x T
2/16 x T
1/16 x T
AS2Cwire Serial Interface Addressing
Address
EN/SET
Rising Edges
Data Register
0
1
2
3
4
5
6
17
18
19
20
21
22
23
F1 and F2 Current Scale
F1 Current Scale
F2 Current Scale
HI/LO
ON/OFF
Timer
Voltage/Current Mode
HI/LO Scale Register (Address 3)
Data
F1
F2
1
2
3
4
LO
HI
LO
HI
LO
HI
HI
LO
Voltage Register (Address 6)
Data
MODE
1
2
Current
Voltage
ON/OFF Register (Address 4)
Data
MODE
1
2
ON
OFF
Thermal Protection
The AAT3170 has a thermal protection circuit that will
shut down the charge pump if the die temperature rises
above the thermal limit, as is the case during a short
circuit of the OUT pin.
AS2Cwire Serial Interface Timing
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
Address
10
2
17
18
1
0
2...
n <= 16
1
Data Reg 1
0
Data Reg 2
0
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n-1
3170.2007.11.1.2
PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Applications Information
LO scale by just giving a single burst of data edges. The
address edges are not needed because all registers are
reset during shutdown and address 0 is the default.
Further, a single burst of data edges can be used to
change from one setting to another for the last address.
The address register is not reset after each write; therefore, submitting address edges is only required when
changing the address.
AS2Cwire Programming
Generally, programming the AAT3170 is achieved by
submitting bursts of address and data edges to the EN/
SET pin. However, in some cases multiple bursts of
address and data are needed to enable a particular operating mode. In other cases, only a single burst of data
edges is required.
Additional Applications
To enable both flash channels to a current setting on the
LO scale, the user submits a single burst of address and
data edges. To enable both flash channels to a current
setting on the HI scale, the user must submit a burst of
address and data edges to program the current setting
level, and then submit a second burst of address and
data edges to program the HI/LO scale register to the HI
scale.
The constant voltage mode feature of the AAT3170
allows the user to combine the flash feature with additional applications. Additional applications such as auxiliary lighting and status LEDs can be added while eliminating the need for an additional power supply, which is
normally required. Since the constant voltage mode can
supply a regulated output at up to 200mA load, it is
capable of driving ten LEDs at 20mA each. It is suitable
for keypad lighting, status lighting, and other applications where a 4.5V power supply could be used.
Shortcuts can also be used. If the device is in shutdown,
both flash channels can be enabled to a setting on the
C1
1μF
C1+
2.7V to 5.5V
C2
1μF
C1-
C2+
C2-
VIN
VOUT
C IN
4.7μF
C OUT
2.2μF
AAT3170
EN/SET
EN/SET
Flash
LED
F1
CT
F2
AUX_EN
GND
Figure 1: Flash Plus Auxiliary Lighting.
C1
1μF
C1+
2.7V to 5.5V
C1-
C2+
C2+
VOUT
VIN
C IN
4.7μF
EN/SET
C2
1μF
C OUT
2.2μF
AAT3170
EN/SET
F1
CT
F2
Flash
LED
STAT1
STAT2
GND
Figure 2: Flash Plus Status Lighting.
3170.2007.11.1.2
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PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
When enabling constant voltage mode, the LED channels
F1 and F2 are automatically disabled so current does not
flow through the flash LED during constant voltage
mode. Because of this, very little programming is
required. The user just addresses the voltage mode register and programs it to voltage mode.
In 1.5X mode, the output voltage can be boosted to 3/2
the input voltage. The 3/2 conversion ratio introduces a
corresponding 1/2 increase in input current. For ideal
conversion, the 1.5X mode efficiency is given by:
η=
LED Selection
The AAT3170 is designed to drive high-intensity white
LEDs. It is particularly suitable for LEDs with an operating forward-voltage in the range of 4.2V to 1.5V.
The charge pump device can also drive other loads that
have similar characteristics to white LEDs. For various
load types, the AAT3170 provides a high-current, programmable ideal constant current source.
Similarly, when the input falls further, such that 1.5X
mode can no longer sustain LED current, the device will
automatically switch to 2X mode. In 2X mode, the output voltage can be boosted to twice the input voltage.
The doubling conversion ratio introduces a corresponding doubling of the input current. For ideal conversion,
the 2X mode efficiency is given by:
Device Power Efficiency
η=
The AAT3170 power conversion efficiency depends on
the charge pump mode. By definition, device efficiency
is expressed as the output power delivered to the LED
divided by the total input power consumed.
η=
POUT
PIN
When the input voltage is sufficiently greater than the
LED forward voltage, the device optimizes efficiency by
operating in 1X mode. In 1X mode, the device is working
as a bypass switch and passing the input supply directly
to the output. The power conversion efficiency can be
approximated by:
η=
VF · ILED VF
≈
VIN · IIN
VIN
Due to the very low 1X mode quiescent current, the
input current nearly equals the current delivered to the
LED. Further, the low-impedance bypass switch introduces negligible voltage drop from input to output.
The AAT3170 further maintains optimized performance
and efficiency by detecting when the input voltage is not
sufficient to sustain LED current. The device automatically switches to 1.5X mode when the input voltage
drops too low in relation to the LED forward voltage.
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VF
VF · ILED
=
VIN · 1.5IIN 1.5 · VIN
VF
VF · ILED
=
VIN · 2IIN
2 · VIN
Capacitor Selection
Careful selection of the four external capacitors (CIN, C1,
C2, and COUT) is important because they will affect turnon time, output ripple, and transient performance.
Optimum performance will be obtained when low equivalent series resistance (ESR) (<100mΩ) ceramic capacitors are used. A value of 1μF for the flying capacitors is
a good starting point when choosing capacitors. If the
LED current sinks are only programmed for light current
levels, then the capacitor size may be decreased.
Ceramic composition capacitors are highly recommended
over all other types of capacitors for use with the
AAT3170. Ceramic capacitors offer many advantages
over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is
lowest cost, has a smaller PCB footprint, and is nonpolarized. 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 composition, and ambient
temperature. Capacitor ESR is typically measured in
milliohms for ceramic capacitors and can range to more
than several ohms for tantalum or aluminum electrolytic
capacitors.
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3170.2007.11.1.2
PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1μF are typically made
from NPO or C0G materials. NPO and C0G materials
typically have tight tolerance and are stable over temperature. Large capacitor values are typically composed
of X7R, X5R, Z5U, or Y5V dielectric materials. Large
ceramic capacitors are often available in lower-cost
dielectrics, but capacitors greater than 4.7μF are not
typically required for AAT3170 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.
PCB Layout
To achieve adequate electrical and thermal performance,
careful attention must be given to the PCB layout. In the
worst-case operating condition, the chip must dissipate
considerable power at full load. Adequate heat-sinking
must be achieved to ensure intended operation.
top layer PCB copper during the re-flow process. This
area should also be connected to the top layer ground
pour when available. Further, multiple copper plated
thru-holes should be used to electrically and thermally
connect the top surface paddle area to additional ground
plane(s) and/or the bottom layer ground pour.
The chip ground is internally connected to both the
paddle and the GND pin. The GND pin conducts large
currents and it is important to minimize any differences
in potential that can result between the GND pin and
exposed paddle. It is good practice to connect the GND
pin to the exposed paddle area using a trace as shown
in Figure 3.
The flying capacitors C1 and C2 should be connected
close to the chip. Trace length should be kept short to
minimize path resistance and potential coupling. The
input and output capacitors should also be placed as
close to the chip as possible.
Figure 3 illustrates an example of an adequate PCB layout. The bottom of the package features an exposed
metal paddle. The exposed paddle acts, thermally, to
transfer heat from the chip and, electrically, as a ground
connection.
The junction-to-ambient thermal resistance (θJA) for the
package can be significantly reduced by following a
couple of important PCB design guidelines.
The PCB area directly underneath the package should be
plated so that the exposed paddle can be mated to the
3170.2007.11.1.2
www.analogictech.com
Figure 3: Example PCB Layout.
13
PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN33-12
SZXYY
AAT3170IWP-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor
products that are in compliance with current RoHS standards, including the requirement that lead not
exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at
http://www.analogictech.com/pbfree.
Package Information3
TDFN33-12
Index Area
0.43 ± 0.05
0.1 REF
C0.3
0.45 ± 0.05
2.40 ± 0.05
3.00 ± 0.05
Detail "A"
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
0.23 ± 0.05
Pin 1 Indicator
(optional)
0.05 ± 0.05
0.23 ± 0.05
0.75 ± 0.05
Detail "A"
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
14
www.analogictech.com
3170.2007.11.1.2
PRODUCT DATASHEET
AAT3170
ChargePumpTM
High Current LED Flash Driver Charge Pump IC
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual
property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and
conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate
design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to
support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other
brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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