AMETHERM AME5144

AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n General Description
n Features
The AME5144 is an efficient driver for up to ten white
LED applications. They are ideal for large LCD backlight
displays in Cell Phone, PDAs, and other handheld devices.
The AME5144 is switch-mode boost converter with constant LED current, rather than output voltage. The series
connection allows the LED currents to be identical for uniform brightness and minimizes the number of trace to the
LEDs. The AME5144 drives series-connected LEDs to
controlled-current pin which connected a typically 13Ω
sense resistor, not an expensive fraction-ohm value.
l Up to 10 LEDs at 25mA
l 86% Efficiency
l 1.7% Current-Regulation Accuracy
l Output Overvoltage Protection
l Flexible Dimming Control
Analog
Direct-PWM Internal Filter
l 1MHz PWM Switching Frequency
Fast 1MHz current-mode PWM operation allows for small
input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. Soft-start eliminates inrush current during startup. To control LED brightness, the LED current can be pulsed by applying a single
analog/PWM signal with a frequency range from 200Hz to
30KHz for the control pin CTRL.
The AME5144 is available in space saving, 8 pin, 3mm x
3mm x 0.75mm DFN package.
l 0.1uF Output Capacitor
l Soft-Start Eliminates Inrush Current
l 2.6V to 5.5V Input Range
l 0.3uA Shutdown current
l DFN 3mm x 3mm x 0.75mm Package with
Exposed Paddle
l All AME’ s Lead Free Products Meet RoHS
Standards
n Applications
l Cell Phones and Smart Phones
C
l PDAs, Palmtops, and Wireless Handhelds
l e-Books and Subnotebooks
l White LED Display Backlighting
ie
S
-
Rev.D.01
1
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Typical Application
L=22µH
Output
Up to 37V
VIN
CIN
OUT
SW
2.2µF
COUT
0.1µF
AME5144
IN
Analog or
PWM Dimming
PGND
CTRL
200Hz to 30KHz
CS
GND
COMP
CCOMP
0.1µF
2 to 10 LEDs
RSENSE
13Ω
n Function Block Diagram
170mV
Comp
Shutdown
8.2ms
CTRL
Bright
Control
OVLO
OUT
Gm
CS
SW
Ramp
Generator
PWM
Control
Driver
PGND
GND
Oscillator
2
Current
Limit
UVP
IN
Rev. D.01
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Pin Configuration
DFN-8C
(3mmx3mmx0.75mm)
Top View
8
7
6
5
AME5144-AVAxxx
1. OUT
2. IN
3. CTRL
4. CS
AME5144
5. COMP
6. GND
7. PGND
1
2
3
4
8. SW
* Die Attach:
Conductive Epoxy
n Pin Description
Pin Number
Pin Name
1
OUT
2
IN
Pin Description
Overvoltage Sense. When OUT is greater than 38.5V(Typ.), the internal nchannel MOSFET turns off until OUT drops below 37V(Min), then the IC reenters
soft-start Connect a 0.1uf ceramic capacitor from OUT to ground. In shutdown,
VOUT is one diode drop below VIN .
C
Input Voltage Supply. The input voltage range is 2.6V to 5.5V. Connect a
2.2uF ceramic capacitor from IN to GND.
Brightness Control pin. Either an Analog or PWM control signal can be used.
ie
The PWM signal must be between 200Hz and 30KHz. Varying the voltage from
+0.24V to +1.65V adjusts the brightness from dim to 100% brightness,
respectively. Any voltage above +1.65V does not increase brightness. Hold
CTRL below 100mV to shut down the IC after an 8.2ms delay.
3
CTRL
4
CS
Current Sense Feedback input. Connect a resistor from CS to GND to set the
LED bias current. The voltage at CS regulates to VCRTL/5 or 0.330V.
5
COMP
Compensation input. Connect a 0.1µF Ceramic Capacitor(Ccomp) from COMP
to GND. Ccomp stabilizes the converter, controls soft-start and lowpass filters
direct PWM dimming at CTRL. Ccomp discharges to 0V through an internal
20KΩ resistor in showdown.
6
GND
7
PGND
Power Ground. Connect to PGND and exposed pad directly under the IC.
8
SW
Inductor Connection. Connect SW to the node between the inductor and
schottky diode. SW is high impedance in shutdown.
Rev.D.01
Ground. Connect to PGND and exposed pad directly under the IC.
3
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Ordering Information
AME5144 - x x x xxx
Output Voltage
Number of Pins
Package Type
Pin Configuration & Special Feature
Pin Configuration &
Special Feature
A
(DFN-8C)
1. OUT
2. IN
3. CTRL
4. CS
5. COMP
6. GND
7. PGND
8. SW
Package
Type
Number of
Pins
V: DFN
A: 8
Output Voltage
ADJ: Adjustable
n Available Options
Part Number
Marking*
Output Voltage
Package
Operating Ambient
Temperature Range
AME5144-AVAADJ
A5144
AMYMXX
ADJ
DFN-8C
-40OC to +85OC
Note:
1. The first 2 places represent product code. It is assigned by AME such as AM.
2. Y is year code and is the last number of a year. Such as the year code of 2008 is 8.
3. A bar on top of first letter represents Green Part such as A5144.
4. The last 3 places MXX represent Marking Code. It contains M as date code in "month", XX as LN code and
that is for AME internal use only. Please refer to date code rule section for detail information.
5. Please consult AME sales office or authorized Rep./Distributor for the availability of output voltage and package
type.
4
Rev. D.01
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Absolute Maximum Ratings
Parameter
Maximum
Unit
-0.3 to 6.0
V
-0.3 to (V IN + 0.3)
V
SW, OUT to GND
-0.3 to 40
V
PGND to GND
-0.3 to 0.3
V
VIN , to GND
CTRL, CS, COMP, to GND
B*
ESD Classification
Caution: Stress above the listed absolute maximum rating may cause permanent damage to the device.
* HBM B: 2000V ~ 3999V
n Recommended Operating Conditions
Parameter
Rating
Unit
Storage Temperature Range
-65 to +150
o
Ambient Temperature Range
-40 to +85
o
Junction Temperature Range
-40 to +125
o
C
C
C
C
n Thermal Information
Parameter
ie
Package
Die Attach
Thermal Resistance*
(Junction to Case)
Thermal Resistance
(Junction to Ambient)
DFN-8C
Conductive
Epoxy
Symbol
Maximum
θJC
17
o
C/W
θJA
125
o
C/W
PD
800
Internal Power Dissipation
Solder Iron (10 Sec)**
350
Unit
mW
o
C
* Measure θJC on backside center of molding compund if IC has no tab.
** MIL-STD-202G 210F
Rev.D.01
5
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Electrical Specifications
VIN = 3V, L=22µH, CIN=2.2µF, COUT=0.1µF, CCOMP=0.1µF, RSENSE =13Ω, TA = 25oC, unless otherwise noted.
Parameter
Input voltage
Symbol
Test Condition
VIN
Typ
Max Units
2.6
5.5
V
37
V
2.55
V
Adjustable Output Range
VOUT
Note 1
VIN -VD
Input Undervoltage Locked
UVP
Rising edge
2.10
Input Undervoltage Locked
Hysteresis
UVP
Hysteresis
2.38
30
mV
Quiescent Current
IQ
No Switching, VCS=0.5V
0.5
0.7
mA
Shutdown Current
ISHDN
CTRL=GND,
VOUT=VIN
0.3
2
µA
Over Voltage Protection
OVP
VOUT Rising
38.5
40
V
Over Voltage Protection
Hysteresis
OVP,HYST
OUT Input Bias Current
IB,OUT
VCTRL=1.5V,
VCS
CS Input Bias Current
ICS
VCS=VCTRL/5
VCS(MAX)
VCTRL=3V
CTRL Input Resistance
VIN=2.6V to 5.5V
RCTRL
VDM
CTRL Dual-Mode Hysteresis
VDM
Hysteresis
V
20
35
0.01
1
µA
0.290 0.300 0.310
V
0.01
1
µA
330
347
mV
310
VCTRL(MAX)
CTRL Dual-Mode Threshold
CTRL Shutdown Enable Delay
9
OUT=IN,
CTRL=GND
CTRL to CS Regulation
CS Maximum Brightness Clamp
Voltage
CTRL Voltage for CS Maximum
Brightness Clamp
37
2
VOUT=32V, VCTRL>0.24V
6
Min
1.65
VCTRL<=1.5V
V
250
500
780
KΩ
100
170
240
mV
5
Note 2
6.0
8.2
mV
10.5
mS
Rev. D.01
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Electrical Specifications (contd.)
Parameter
Symbol
Test Condition
Min
Typ
CS to Comp Transconductance
Gm
VCOMP=1.5V
32
50
COMP Input Resistance to
Ground
In shutdown, UVLO or OVLO
Switch Frequency
fOSC
Minimum Duty Cycle
DMIN
Max Units
82
20
0.75
1.0
PWM Mode
12
Pulse Skipping
0
µS
KΩ
1.25
MHz
%
Maximum Duty Cycle
DMAX
CTRL=IN, CS=GND
94
Switch On-Resistance
RDS,ON
ISW =190mA
0.8
1.35
Ω
Switch Leakage Current
ISW,LK
VSW =37V,
CTRL=GND
0.01
5
µΑ
Switch Current Limit
ISW,CL
Duty Cycle=90%
700
900
mA
500
95
%
Note 1: VD is the forward-voltage drop of the Schottky diode in Typical Application.
Note 2: Time from CTRL going below the Dual-Mode threshold to IC shutdown.
C
ie
Rev.D.01
7
AME
AME5144
n Detailed Description
The high efficiency and small size of the AME5144 make
them ideally suited to driver up to ten series-connected
LEDs. They operate as a boost DC-DC converter that controls output current rather than voltage. A low 300mV current-sense threshold minimized the losses. The AME5144
provide even illumination by sourcing the same output current through each LED, eliminating the need for expensive
factory calibration. The fast 1MHz internal oscillator allows for small inductor and small input and output capacitors while minimizing input and output ripple.
The single analog control input (CTRL) allows easy adjustment of LED brightness and on/off control. This allows
simple logic-level on/off control, analog voltage control, or
PWM duty-cycle control of both brightness and shutdown.
In shutdown, supply current is reduced to a low 0.3µA
(Typ.). A soft-start gradually illuminates the LEDs, eliminating the inrush current during startup.
Shutdown
The AME5144 enter shutdown when VCTRL is less than
100mV for more than 8.2ms. When shutdown, the supply
current is reduced to 0.3µA (Typ.) approximately.
The 0.3uA supply current is applied for the voltage-detection circuitry. CCOMP is discharge during shutdown, allowing the device to reinitiate soft-start when enabled. Although the internal n-channel MOSFET does not switch in
shutdown, there is still a DC current path between the
input and the LEDs through the inductor and Schottky diode. The minimum forward voltage of the LED array must
exceed the maximum input voltage to ensure that the LEDs
remain off in shutdown. However, with two or more LEDs,
the forward voltage is enough to keep leakage current low,
less than 1µA (Typ.).
Soft-Start
The AME5144 attain soft-start by charging CCOMP gradually with a current source. When V COMP rises above 1.25V,
the internal MOSFET begins switching at a reduced duty
cycle. When VCOMP rises above 2.25V, the duty cycle is
at its maximum. See the Typical Operation Characteristics for an example of soft-start operation.
8
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
Over Voltage Protection
OVP is designed to prevent the output voltage from exceeding the maximum switch voltage rating of 38.5V (Typ.).
The protection circuitry stops the internal MOSFET from
switching. There is a 1.5V hysteresis associated with
this circuitry which will cause the output to fluctuate between 38.5V and 37V.
Adjusting LED Current
Adjusting the output current of the AME5144 changes
the brightness of the LEDs. An analog input (CTRL) and
the sense-resistor values set the output current. Output
current is given by:
ILED =VCTRL/(5xRSENSE)
The VCTRL voltage range for adjusting output current is
0.24V to 1.65V. To set maximum current, calculate
RSENSE when VCTRL is at its maximum as follows:
RSENSE=1.65V / (5 x ILED )
Power dissipation in RSENSE is typical less than 10mW,
allowing the use of small surface-mount resistor.
PWM Dimming Control
A. Using DC Signal for CTRL Pin
For CTRL, applying a DC signal in the range of 0.24V to
1.65V control the LED current. CTRL can be overdriven;
however, applying a CTRL greater than 1.65V does not
increased the LED current above the level at 1.65V.
B. Using PWM signal forc CTRL pin
The CTRL input is used as a digital input allowing LED
brightness control with a logic-level PWM signal applied
directly to CTRL. The frequency range is from 200Hz to
30KHz, while 0% duty cycle corresponds to minimum current, and 100% duty cycle corresponds to full current.
The error amplifier and compensation capacitor form a
low pass filter so PWM dimming results in DC current to
the LEDs without the need for any additional RC filters.
Rev. D.01
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
Capacitor Selection
Schottky Diode Selection
Ceramic capacitors with X5R, X7R, or better dielectric
are recommended for stable operation over the entire operating temperature range. The exact values of input and
output capacitors are not critical. The typical value for
input capacitor is 2.2µF, and the typical value for output
capacitor is 0.1µF. Higher values capacitors can be used
to reduce input and output ripple, but at the expense of
size and higher cost. CCOMP stabilizes the converter and
control soft-start. Connect a 0.1µF capacitor from COMP
to GND.
Inductor values range from 10µH to 47µH. A 22µH inductor optimizes the efficiency for most applications while
maintaining low 12mVp-p input ripple. Inductor with low
DCR can be more efficiency. To prevent core saturation,
ensure that the inductor-saturation current rating exceeds
the peak inductor current for the application. Calculate
the peak inductor current with the following formula:
VOUT ( MAX ) × I LED( MAX )
0.9 × VIN ( MIN )
I DIODE( RMS) = I OUT × I PEAK
200mA, 40V Schottky diode SOD-523 or Central Semiconductor CMOSH-4E are recommended for applications.
Inductor Selection
I PEAK =
The high switching frequency of the AME5144 demands
a high-speed rectification diode (D1) for optimum efficiency.
A Schottky diode is recommended due to its fast recovery
time and low forward-voltage drop. Ensure that the diode's
average and peak current rating exceed the average output current and peak inductor current. In addition, the
diode's reverse breakdown voltage must exceed V OUT. The
RMS diode current can be approximated from:
+
VIN ( MIN ) × 0.9us
2× L
Layout Consideration
Due to fast switching waveforms and high-current paths,
careful PC board layout is required. When laying out a
board, minimum trace lengths between the IC and RSENSE,
the inductor, the diode, the input capacitor and output capacitor. Keep trace short and wide. Keep noisy traces,
such as the SW node trace, away from CS.
22µH, 250mA inductor Murata LQH32CN220K and
The input bypass capacitor CIN should be placed as close
C to the IC as possible. This will reduce copper trace resisSumida CDRH5D16NP- 220MB are recommended.
tance, which effect the input voltage ripple of the IC. The
output capacitor, COUT, should also be placed close to the
i e IC and connected directly between the OUT and GND pins.
PGND and GND should be connected directly to the exposed paddle underneath the IC. The ground connections
of CIN and COUT should be as close together as possible.
Any copper trace connections with the COUT capacitor can
increase the series resistance which directly effects output ripple and efficiency. The current setting resistor,
RSENSE, should be kept close to the CS pin to minimize
copper trace connections that can inject noise in to the
system. The traces from IN to the inductor and from
Schottky diode to the LEDs can be longer.
Rev.D.01
9
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
Duty Cycle
The maximum duty cycle of the switching regulator determines the maximum boost ratio of output-to-input voltage that the converter can attain in mode of operation.
The duty cycle for a given boost application is defined as:
This applies for continuous mode operation.
D=
VOUT + VDIODE - V IN
VOUT + VDIODE - VSW
Calculating Load Current
The load current is related to the average inductor current by the relation:
ILOAD = IIND (AVG) x (1 - D)
Where “ D” is the duty cycle of the application. The
switch current can be found by:
ISW = IIND (AVG) + 1 /2 (IRIPPLE)
Inductor ripple current is dependent on inductance, duty
cycle, input voltage and frequency:
IRIPPLE = D x (V IN-V SW) / (f x L)
Combining all terms, we can develop an expression
which allows the maximum available load current to be
calculated:
ILOAD = ( 1-D ) x ( ISW (max) -
10
D ( VIN-VSW )
)
2fL
Rev. D.01
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
Efficiency vs LED Current
Efficiency vs Input Voltage
95
100
3 LEDs
95
6 LEDs
3 LEDs
90
4 LEDs
90
85
Efficiency(%)
Efficiency(%)
85
80
75
6 LEDs
70
8 LEDs
65
60
10 LEDs
80
75
8 LEDs
10 LEDs
70
65
60
55
55
50
45
50
2
3
4
5
6
0
5
10
Input Voltage(V)
15
20
25
LED Current(mA)
LED Current vs Ambient Temperature
LED Current vs Direct-PWM Dimming
26
30
24
25
LED Current(mA)
LED Current(mA)
22
20
15
10
20
18
ILED =15mA
16
14
12
5
C
0
0
20
40
60
80
10
8
-40
100
Duty Cycle(%)
-20
0
20
40
60
80
100
Temperature(o C)
ie
Switching Waveforms
Soft-Start And Shutdown Response
20mV/div
AC-coupled
VIN
VLX
10V/div
VOUT
200mV/div
AC-coupled
IL
100mA/div
400 ns/div
Rev.D.01
VCTRL
2V/div
IIN
100mA/div
ILED
50mA/div
VOUT
10V/div
20ms/div
11
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
Ctrl Step Response
Direct-PWM Dimming Response
V CTRL
1V/ div
VCTRL
2V/div
32kHZ 50%
Duty cycle
IIN
100mA/div
V IN
20mV/div
AC -coupled
ILED
50mA/div
V OUT
500 mV/div
AC -coupled
VOUT
10V /div
I LED
20ms /div
10m A/div
10µs/div
VFB vs VIN
310
308
306
TA = -40OC
VF B(mV)
304
302
300
298
296
TA =85OC
T A=25OC
294
292
290
2.6
3.6
4.6
5.6
VIN(V)
12
Rev. D.01
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Date Code Rule
Month Code
1: January 7: July
2: February 8: August
3: March
9: September
4: April
A: October
5: May
B: November
6: June
C: December
n Tape and Reel Dimension
DFN-8C
(3mmx3mmx0.75mm)
P
PIN 1
W
AME
AME
C
ie
Carrier Tape, Number of Components Per Reel and Reel Size
Rev.D.01
Package
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
DFN-8C
(3x3x0.75mm)
12.0±0.1 mm
4.0±0.1 mm
3000pcs
330±1 mm
13
AME
High Efficiency, 37V Step-Up
Converter for 2 to 10 White LEDs
AME5144
n Package Dimension
DFN-8C (3mmx3mmx0.75mm)
b
D
e
L
E
E1
PIN #1
TOP VIEW
D1
BOTTOM VIEW
A
G1
G
REAR VIEW
SYMBOLS
14
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
0.700
0.800
0.028
0.031
D
2.900
3.100
0.114
0.122
E
2.900
3.100
0.114
0.122
e
0.600
0.700
0.024
0.028
D1
2.200
2.400
0.087
0.094
E1
1.400
1.600
0.055
0.063
b
0.200
0.320
0.008
0.013
L
0.375
0.575
0.015
0.023
G
0.153
0.253
0.0060
0.010
G1
0.000
0.050
0.0000
0.002
Rev. D.01
www.ame.com.tw
E-Mail: sa[email protected]
Life Support Policy:
These products of AME, Inc. are not authorized for use as critical components in life-support
devices or systems, without the express written approval of the president
of AME, Inc.
AME, Inc. reserves the right to make changes in the circuitry and specifications of its devices and
advises its customers to obtain the latest version of relevant information.
 AME, Inc. , December 2008
Document: 1241-DS5144-D.01
Corporate Headquarter
AME, Inc.
2F, 302 Rui-Guang Road, Nei-Hu District
Taipei 114, Taiwan.
Tel: 886 2 2627-8687
Fax: 886 2 2659-2989