Analogic AAT3170IWP-T1 High current led flash driver charge pump ic Datasheet

AAT3170
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.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
The dual charge pump in the AAT3170 is capable
of delivering 600mA output current. Two currentcontrolled 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.
ChargePump™
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
•
•
•
•
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+
C IN
4.7µF
C2-
VOUT
VIN
C OUT
2.2µF
AAT3170
Flash
LED 1
Flash
LED 2
EN/SET
EN/SET
F1
CT
CT
0.1µF
3170.2006.10.1.0
F2
GND
1
AAT3170
High Current LED Flash Driver Charge Pump IC
Pin Descriptions
Pin #
Symbol
Function
1, 12
2
3
4
5
6
7
8
VIN
C1+
C1GND
F1
F2
EN/SET
CT
9
10
11
EP
C2C2+
VOUT
Input power supply pin. Requires 4.7µF bypass capacitor to ground.
Flying capacitor C1 positive terminal. Connect a 1.0µF 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 capacitor between C2+ and C2-.
Charge pump output. Requires 2.2µF 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
3170.2006.10.1.0
AAT3170
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
2.0
°C/W
W
Thermal Information2
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.
3170.2006.10.1.0
3
AAT3170
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
VIN
Input Voltage Range
ICC
Operating Current
ISHDN(MAX)
IOUT(MAX)2
VIN Pin Shutdown Current
Maximum Output Current
I(D-Match)
Current Matching Between
Outputs; High Current
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
Current Matching Between
Outputs; Low Current
Output Current Accuracy
Clock Frequency
Voltage Mode Regulation
Soft-Start Time
Min
Typ Max Units
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
Enable Threshold Low
VIN = 2.7V
Enable Threshold High
VIN = 5.5V
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
5.5
V
10
µA
300
2.0
3.0
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
4.0
6.0
1.0
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.
2. Mounted on an FR4 board.
4
3170.2006.10.1.0
AAT3170
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
50
95mA/ch
VF = 3.1V
40
30
20
VOUT
(2V/div)
VSINK
(1V/div)
IIN
(200mA/div)
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)
Time (200µs/div)
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)
3170.2006.10.1.0
Time (200µs/div)
5
AAT3170
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
VIN
(100mV/div)
Output Voltage (V)
4.7
VOUT
(200mV/div)
VSINK
(200mV/div)
IOUT = 10mA
4.6
4.5
4.4
IOUT = 80mA
4.3
IOUT = 30mA
IOUT = 120mA
4.2
4.1
4.0
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)
Time (2µs/div)
Voltage Mode Load Regulation
Flash Timer Duration
4.8
1.8
4.7
1.6
4.6
VIN = 4.2V
VIN = 3.7V
4.5
4.4
VIN = 3.3V
4.3
85°C
1.4
1.2
1.0
25°C
0.8
0.6
4.2
-40°C
0.4
0
50
100
150
200
Load Current (mA)
6
Flash Time (s)
Output Voltage (V)
(CT = 0.1µF; Data = 1)
250
300
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)
3170.2006.10.1.0
AAT3170
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
TLAT vs. VIN
(CT = 0.1µF; Data = 16)
350
140
300
85°C
100
80
25°C
60
250
TLAT (µs)
Flash Time (ms)
120
-40°C
25°C
200
150
85°C
100
40
50
0
20
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
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)
Input Voltage (V)
TOFF vs. VIN
VIH vs. VIN Over-Temperature
1.0
350
300
-40°C
0.9
25°C
200
150
-40°C
0.8
VIH (V)
250
TOFF (µs)
-40°C
85°C
0.7
85°C
25°C
0.6
100
50
0.5
0
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
Input Voltage (V)
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
Input Voltage (V)
VIL vs. VIN Over-Temperature
1.0
0.9
-40°C
VIL (V)
0.8
0.7
0.6
85°C
25°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
Input Voltage (V)
3170.2006.10.1.0
7
AAT3170
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
8
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 voltage 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
3170.2006.10.1.0
AAT3170
High Current LED Flash Driver Charge Pump IC
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 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 on-time, 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.
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.
3170.2006.10.1.0
9
AAT3170
High Current LED Flash Driver Charge Pump IC
AS2Cwire latches data or address after the EN/SET
pin has been held high for time TLAT. 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, 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 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.
AS2Cwire Serial Interface Addressing
EN/SET
Address Rising Edges
0
17
1
2
3
4
5
6
18
19
20
21
22
23
Data Register
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)
10
Data
F1
F2
1
2
3
4
LO
HI
LO
HI
LO
HI
HI
LO
ON/OFF Register (Address 4)
Data
MODE
1
2
ON
OFF
Timer Register (Address 5)
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
Voltage Register (Address 6)
Data
MODE
1
2
Current
Voltage
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.
3170.2006.10.1.0
AAT3170
High Current LED Flash Driver Charge Pump IC
AS2Cwire Serial Interface Timing
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
2
Address
17
18
1
0
0
Data Reg 2
0
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.
n <= 16
1
Data Reg 1
Applications Information
2...
n-1
ting 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.
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 100mA load, it is capable of driving five
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 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 set-
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.
3170.2006.10.1.0
11
AAT3170
High Current LED Flash Driver Charge Pump IC
C1
1µF
C1+
2.7V to 5.5V
C2
1µF
C1-
C2+
C2-
VOUT
VIN
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
CIN
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.
LED Selection
Device Power Efficiency
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 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.
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.
12
η=
POUT
PIN
3170.2006.10.1.0
AAT3170
High Current LED Flash Driver Charge Pump IC
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.
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=
VF
VF · ILED
=
VIN · 1.5IIN 1.5 · VIN
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:
η=
3170.2006.10.1.0
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 turn-on 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 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 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.
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.
13
AAT3170
High Current LED Flash Driver Charge Pump IC
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.
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.
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 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.
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 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.
Figure 3: Example PCB Layout.
14
3170.2006.10.1.0
AAT3170
High Current LED Flash Driver Charge Pump IC
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN33-12
QLXYY
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 Information
TDFN33-12
2.40 ± 0.05
Detail "B"
3.00 ± 0.05
Index Area
(D/2 x E/2)
0.3 ± 0.10 0.16 0.375 ± 0.125
0.075 ± 0.075
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
Pin 1 Indicator
(optional)
0.23 ± 0.05
Detail "A"
0.45 ± 0.05
0.1 REF
0.05 ± 0.05
0.229 ± 0.051
+ 0.05
0.8 -0.20
7.5° ± 7.5°
Option A:
C0.30 (4x) max
Chamfered corner
Side View
Option B:
R0.30 (4x) max
Round corner
Detail "B"
Detail "A"
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
© 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.
Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech
warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. 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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
3170.2006.10.1.0
15
Similar pages