AOZ1935QI - Alpha & Omega Semiconductor

AOZ1934/1935
High Efficiency Boost 20-, 30- LED Driver
General Description
Features
The AOZ1934/5 is an ideal power solution for white LED
backlighting for medium to small size LCD panels. It is a
highly integrated step up DC-DC converter with input
voltage range from 2.7V to 25V, accommodating
1-, 2-, 3-, or 4-cell lithium ion batteries or 3.3V, 5V, 12V
or 20V regulated supplies. The AOZ1934/5 integrates a
40V power MOSFET as well as compensation and soft
start circuitry, which results in a simpler and smaller
solution with much fewer external components. A high
switching frequency (800kHz) allows the use of a smaller
inductor and capacitor to further reduce the solution size.
 Wide input range: 2.7V to 25V
Each of the regulated current sinks in the AOZ1934/5
provides 20mA factory programmed current. With a
maximum of 40V at the output of the step-up converter,
each string can connect up to ten LEDs in series, for a
total of 20 LEDs for AOZ1934 and 30 LEDs for AOZ1935.
The AOZ1934/5 is equipped with fast PWM dimming
control for wide dimming range and has an enable pin for
IC ON/OFF control. Various protection features are built
into the AOZ1934/5, including cycle-by-cycle input
current limit protection, output over-voltage protection,
LED fault (open or short) protection and thermal
shutdown protection. The leakage current in shutdown
mode is 0.1µA.
The AOZ1934/5 is available in a 16-lead 3 x 3 x 0.75mm
thin QFN package.
 Drive up to 30 LEDs
– AOZ1934 up to 20 LEDs (10s2p)
– AOZ1935 up to 30 LEDs (10s3p)
 Up to 92% efficiency
 High frequency step-up converter (800kHz)
 Highly integrated solution
– Integrated 40V Power MOSFET
– Internal compensation and soft start
 Integrated current sinks:
AOZ1934 – 2 channels, AOZ1935 – 3 channels
– ±2% Typ. current accuracy
– 1.5% Typ. current matching
 PWM dimming with <1µs delay time
 Low operating quiescent current (500µA)
 LED open/short protection
 Both internal fixed and external adjustable
Over-voltage protection
 Cycle-by-cycle inductor current limit (2.5A)
 0.1µA shutdown current
 Green Package: 3 x 3 QFN-16
 -40°C to +85°C temperature range
Applications
 Netbook
 Tablet PCs
 GPS
 Portable media players
 1-, 2-, 3-, 4-cell Li Ion LED applications
Rev. 1.2 June 2013
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Page 1 of 15
AOZ1935
Typical Application Circuit
LED Power Input
Voltage Range:
3V to 25V
L = 4.7µH
C OUT
C IN
10µF
1µF
White LEDs
AOZ1935
VIN
IC Supply:
2.7V to 5.5V
LX
AVCC
Up to 10 in series
OV
C AVCC
1µF
VOUT
S1
Enable
PWM Dimming
Control
EN
S2
PWM
S3
GND
PAD
PGND
Ordering Information
Part Number
Ambient Temperature Range
Package
Environmental
AOZ1934QI*
-40°C to +85°C
3x3 QFN-16
Green Product
AOZ1935QI
-40°C to +85°C
3x3 QFN-16
Green Product
*Contact manufacturer for product availability
AOS Green Products use reduced levels of Halogens, and are also RoHS compliant.
Please visit www.aosmd.com/media/AOSGreenPolicy.pdf for additional information.
Rev. 1.2 June 2013
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Page 2 of 15
AOZ1935
Pin Configuration
VIN
AVCC PGND PGND
13
OV
12
VOUT
11
14
15
16
1
LX
2
LX
PAD
S1
10
3
PWM
S2
9
4
NC
8
7
S3*
GND
6
5
EN
NC
3x3 QFN-16
(Bottom View)
Pin Description
Pin Number
Pin Name
1, 2
LX
3
PWM
4, 5
NC
Not internally connected
6
EN
IC enable
7
GND
8
S3*
Regulated output current sink #3*
9
S2
Regulated output current sink #2
10
S1
Regulated output current sink #1
11
VOUT
12
OV
Over voltage feedback sense pin. Programmable with a resistor divider, this pin has an
internal 1.2V threshold
13
VIN
Boost converter power supply’s input voltage sense pin
14
AVCC
Input supply pin for the IC
15, 16
PGND
Power Ground pin
PAD
Pin Function
Switching node of the step-up converter
Pulse width controlled dimming input. Connect this pin to AVCC when not used
Analog Ground pin
Output voltage sense pin
Exposed Backside Paddle. Connect to ground for electrical and thermal usage. PAD is
internally connected to Analog Ground pin.
*S3 is only for the AOZ1935.
Rev. 1.2 June 2013
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Page 3 of 15
AOZ1935
Functional Block Diagram
Backlight Unit
LED Power Input
3V to 25V
LX
VOUT
Converter
Control
PGND
Over
Voltage
Control
OV
Up to 10 LEDs
in Series
VIN
S1
ICC Supply
2.7V to 5.5V
AVCC
IC Bias,
Vref
Voltage
Optimizing
Control
S2
GND
S3*
*S3 is only for the AOZ1935
Enable
PWM
Brightness
Control
EN
Constant
Current
Control
Logic
Control
PWN
AOZ1934/35
Rev. 1.2 June 2013
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Page 4 of 15
AOZ1935
Absolute Maximum Ratings (TA=25C unless otherwise noted(1)
Exceeding the Absolute Maximum ratings may damage the device.
Symbol
Value
Unit
Boost Converter Input Voltage
-0.3 to 28
V
AVCC
IC Input Voltage
-0.3 to 6
V
LX, Sx
High Voltage Nodes
-0.3 to 44
V
VOUT
Output Voltage Node
-0.3 to 44
VIN
EN, PWM, OV
Description
Input Nodes
-0.3 to AVCC+0.3
V
TJ
Operating Temperature Range
-40 to 150
C
TS
Storage Temperature Range
-65 to 150
C
300
C
2
kV
TLEAD
ESD
Maximum Soldering Temperature (at leads, 10 seconds)
Human Body Model
Note:
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.
Thermal Capabilities
Symbol
Description
Ambient(2)
Value
Unit
50
C/W
JA
Thermal Resistance – Junction to
PD
Maximum Power Dissipation at TA  25C
2.0
W
Derating Factor Above TA = 25C
-20
mW/C
PD / T
Note:
2. Junction to Ambient thermal resistance is highly dependent on PCB layout. Values are based on thermal properties of the device when soldered to
an EV board.
Rev. 1.2 June 2013
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Page 5 of 15
AOZ1935
Electrical Characteristics
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
IC SUPPLY
Boost Converter Input Range
2.7
25
V
AVCC
IC Supply Voltage Range
2.7
5.5
V
UVLO
IC Supply Under Voltage Lockout
2.65
V
VIN
UVLOHYST
IQ
ISHDN_AVCC
ISHDN_VIN
Rising Edge
2.5
UVLO Hysteresis
0.15
V
IC Standby Current
Not Switching
0.5
mA
IC Operating Current
Switching
1.15
mA
AVCC Pin Shutdown Current
EN = GND
0.1
1.0
µA
VIN Pin Shutdown Current
EN = GND
0.1
1.0
µA
STEP-UP CONVERTER
NMOS On-resistance
0.35
Ω
ILIM
Peak NMOS Current Limit
2.5
A
FSW
Oscillator Frequency
800
kHz
Dmax
Maximum Duty Cycle
95
%
VOV
OV Pin Threshold
1.2
V
VOVP
Internal OVP – VOUT Threshold
40
V
Start-up Time
1
ms
RDS(ON)
TS
92
CURRENT SINK
ID
Output Current Accuracy
Output current matching(3)
V_sov
Current Sink Over-voltage Threshold
TFAULT
Current Sink Fault Delay
Current Setting = 20mA
(DATA = 1), TA=25°C
±1
±4
Current Setting = 20mA
(DATA = 1)
±1
±6
Current Setting = 20mA
(DATA = 1)
1.5
3.5
PWM 100% Duty Cycle
%
%
6.0
V
80
ms
CONTROL
VTH-L
EN, PWM Pin Logic Low Threshold
VTH-H
EN, PWM Pin Logic High Threshold
TPWM(ON)_MIN
0.4
V
1.4
Minimum PWM On Time
V
1
100
µs
FPWM
PWM Dimming Frequency
30000
Hz
TJ-TH
IC Junction Thermal Shutdown
Threshold
150
°C
IC Junction Thermal Shutdown
Hysteresis
15
C
Note:
3.The device is guaranteed to meet performance specifications over the –40°C to +85°C operating temperature range by design, characterization
and correlation with statistical process controls.
4.The current matching between channels is defined as |Id-Iavg|max/Iavg .
Rev. 1.2 June 2013
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Page 6 of 15
AOZ1935
Typical Operating Characteristics
Electrical Efficiency
100
95
Efficiency (%)
90
85
80
75
70
65
60
55
50
2
7
12
17
22
27
Vin (V)
LED Current Regulation
22.90
22.85
LED Current (mA)
22.80
22.75
22.70
22.65
22.60
22.55
22.50
22.45
22.40
2.7
7.7
12.7
17.7
Input Voltage (V)
22.7
PWM Dimming Linearity
Average LED Current (mA)
20
15
10
DBRIT = 1kHZ
DBRIT = 100HZ
DBRIT = 30kHZ
5
0
0
10
20
30
40
50
60
70
80
90
100
PWM Duty Cycle(%)
Rev. 1.2 June 2013
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Page 7 of 15
AOZ1935
Typical Operating Characteristics (Continued)
Start-up Waveform
Switching Waveform
(VIN = 5V, Full Brightness)
(VIN = 2.7V, Full Brightness)
EN
2V/div
LX
20V/div
Vout
20V/div
IS3
20mA/div
IL
1A/div
400µs/div
1µs/div
Switching Waveform
Switching Waveform
(VIN = 3.6V, Full Brightness)
(VIN = 5V, Full Brightness)
LX
20V/div
LX
20V/div
IL
1A/div
IL
1A/div
1µs/div
1µs/div
Switching Waveform
Switching Waveform
(VIN = 12V, Full Brightness)
(VIN = 25-V, Full Brightness)
LX
20V/div
LX
20V/div
IL
1A/div
IL
1A/div
1µs/div
Rev. 1.2 June 2013
1µs/div
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Page 8 of 15
AOZ1935
Typical Operating Characteristics (Continued)
PWM Dimming 10%
PWM Dimming 10%
(VIN = 3.6V, Frequency = 20kHz)
(VIN = 5V, Frequency = 20kHz)
DPWM
5V/div
DPWM
5V/div
VS1
20V/div
VS1
20V/div
IS1
20mA/div
IS1
20mA/div
IL
1A/div
IL
1A/div
10µs/div
10µs/div
PWM Dimming 50%
PWM Dimming 50%
(VIN = 3.6V, Frequency = 20kHz)
(VIN = 5V, Frequency = 20kHz)
DPWM
5V/div
DPWM
5V/div
VS1
20V/div
VS1
20V/div
IS1
20mA/div
IS1
20mA/div
IL
1A/div
IL
1A/div
10µs/div
10µs/div
PWM Dimming 90%
PWM Dimming 90%
(VIN = 3.6V, Frequency = 20kHz)
(VIN = 5V, Frequency = 20kHz)
DPWM
5V/div
DPWM
5V/div
VS1
20V/div
VS1
20V/div
IS1
20mA/div
IS1
20mA/div
IL
1A/div
IL
1A/div
10µs/div
Rev. 1.2 June 2013
10µs/div
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Page 9 of 15
AOZ1935
Typical Operating Characteristics (Continued)
Output, Short-to-Ground
LED Open Protection
(VIN = 5V, Full Brightness)
(VIN = 5V, Full Brightness)
VS3
5V/div
VS3
5V/div
Vout
20V/div
Vout
20V/div
IS3
20mA/div
IS3
20mA/div
IL
1A/div
IL
1A/div
40ms/div
2s/div
LED Short Protection
(VIN = 5V, Full Brightness)
VS3
5V/div
Vout
20V/div
IS3
20mA/div
IL
1A/div
20ms/div
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Page 10 of 15
AOZ1935
Detailed Description
The AOZ1934/5 is a unique current regulated step-up
(boost) converter. Two (or three for AOZ1935) current
regulating devices are integrated to drive two or three
strings of LEDs. Unused channels need to be connected
to ground (GND).
The voltage step-up is accomplished by a boost topology,
using an inductor-based DC-DC switching converter, in
which the inductor serves as an energy storage device in
the system. By integrating a high voltage optimized
MOSFET, the AOZ1934/5 internal switching frequency is
800kHz while still maintaining high power efficiency.
Unlike a traditional DC-DC boost converter with a fixed
output voltage, the AOZ1934/5 dynamically changes its
output voltage regulation parameters depending on the
load. The use of unique control schemes maintains
accurate current regulation in each current sink while
leaving the output voltage at a minimum, increasing the
overall conversion efficiency. The internal step-up
converter dynamically controls the voltage at the output
high enough to drive the LED string with the highest total
forward voltage. The wide input voltage range, from 2.7V
to 25V, allows maximum system flexibility; battery
powered devices using 1-, 2-, 3- or 4-cell Li Ion packs
can share the same power architecture. A low power
2.7V to 5.5V input to supply the IC bias circuitry is
required at AVCC pin.
LED brightness control is based on the popular PWM
dimming scheme via the PWM pin. The EN pin provides
ON/OFF control of the IC. By asserting a logic high on
the EN pin, the converter is enabled and will regulate
each of the current sinks at the factory programmed
current setting.
Application Information
Power Up Sequence
It’s recommended to power up Vin, AVCC, and PWM
dimming in sequence, and EN pin needs to ramp up
simultaneously or later than AVCC, in order to avoid
latch-off, or mis-operation of device. We do not assume
any liability or responsibility for any loss or damage
arising from misuse or inappropriate use of the product.
Current Dimming Using PWM Pin
AOZ1934/5 allows maximum flexibility with a PWM signal
control input which can be used for dimming. The IC
must remain Enabled at EN pin during PWM dimming,
which means the step-up converter is active to reduce
the response time. Combining this with the fast response
of the step-up converter, each LED channel can typically
Rev. 1.2 June 2013
recover from no current within 1µs. This allows very short
PWM on-time or a duty-cycle with fine resolution.
Assume a 50µs minimum on-time for a 100Hz PWM
signal, a 200:1 ratio can be achieved by PWM.
The minimum PWM on-time of 1s is required in
AOZ1934/5’s application, this means minimum PWM
duty cycle of 2% for 20kHz dimming frequency and
0.02% for 200Hz dimming frequency. The amplitude of
PWM signal should not be higher than AVCC, otherwise
test mode will be triggered.
Fault Protection (LED Open or Short)
Each current sink is protected against LED short or
open conditions. If an LED short circuit condition
arises, the current sink continues to regulate until
VSINK > VSOV (6V). When any sink node voltage goes
above VSOV for more than 80ms (while PWM dimming
signal remains high), that channel’s current sink will be
turned off, and other channels will still work if they don’t
trigger this fault condition. For example, if one or more
LEDs on a channel are shorted, that channel’s sink
voltage will increase. If the voltage goes above 6V for
more than 80ms, the Current Sink Fault Protection will be
triggered and only this faulty string will be disabled by
shutting off this current sink. All other channels will
continue normal operation if they don’t have a fault
condition. When PWM dimming control is used, the 80ms
fault delay is accumulated only when PWM signal is high;
the PWM low time is not counted into the fault delay, so
the delay time will be 80ms / DPWM (DPWM is the duty
cycle of the PWM signal).
In case of an LED failing open, the current sink voltage of
the failed string will go close to ground and dominate the
boost converter control loop. As a result the output
voltage will move up to the over-voltage threshold, set
internally to 40V or by the external resistor divider,
whichever is lower. Once the over-voltage incident is
flagged internally, the faulty channel(s) will be disabled.
Then the output voltage of the boost converter will go
back to normal level. During the entire process, the rest
of the LED strings (healthy LED strings) would continue
normal operation.
The fault conditions are reset when the IC is powered
down and up again.
Output Over-Voltage Protection (OVP)
AOZ1934/5 has built in over-voltage protection function
with 40V threshold at VOUT pin. This level is suitable for
applications with ten series LEDs per string. However, for
applications with fewer series LEDs, the user can choose
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Page 11 of 15
AOZ1935
to program a lower over-voltage threshold using the OV
pin. The internal reference voltage to trigger OVP at OV
pin is 1.2V; a resistor divider can be connected as shown
in the following figure and the over voltage threshold can
be derived as

R 
V OUT_OV = 1.2   1 + ------1-
R 2

To limit the leakage current through the divider, make
sure 10M > R1+R2 > 1M. The lower value of the internal
40V OVP and the external OVP set by the resistor divider
determines the system OVP value.
Thermal Shutdown
Thermal shutdown feature is also included in the
AOZ1934/5. When IC junction temperature (TJ) reaches
150C, the IC will immediately enter shutdown mode.
Once TJ drops 15C to around 135C, the IC will be back
to normal operation.
Inductor Selection
A 4.7µH to 10µH inductor is recommended for all the
applications. If high efficiency is a critical requirement, a
low DCR inductor should be selected. The inductor’s
saturation current rating should also exceed the peak
input current.
Rev. 1.2 June 2013
Capacitor Selection
Small size ceramic capacitors with low ESR are ideal for
all the applications. A 10uF input capacitor at VIN, a 1µF
input capacitor at AVCC and a 1µF output capacitor at
VOUT are suggested. The voltage rating of these
capacitors should exceed the maximum possible voltage
at the corresponding pins. For example, for the
application of 3P10S LEDs from input voltage range of
5V to 22V and AVCC = 3.3V, a 25V capacitor is
recommended at the VIN pin, a 50V capacitor is
recommended at the VOUT pin, and a 10V capacitor is
recommended at the AVCC pin.
Diode Selection
Using a schottky diode is recommended because of its
low forward voltage drop and fast reverse recovery time.
The current rating of the schottky diode should exceed
the peak current of the boost converter. The voltage
rating should also exceed the target output voltage. For
applications driving 10 LEDs in series, 50V voltage rating
schottky diode is recommended.
Layout Considerations
PCB layout is very important for high frequency switching
regulators in order to keep the loop stable and minimize
noise. The AVCC pin’s capacitor should be very close to
the IC to get the best decoupling. The path of the
inductor, schottky diode and output capacitor should be
kept as short as possible to minimize noise and ringing.
Please see the AOZ1934/5 evaluation document for
detailed PCB layout guidelines.
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Page 12 of 15
AOZ1935
Package Dimensions, QFN-16 3mm x 3mm x 0.75mm
D
D1
9
12
12
9
8
13
13
8
E1
E
Pin 1 Dot
By Marking
5
5
16
16
Pin 1
Identification
L
1
4
4
TOP VIEW
1
e
Detail "A"
R0.3(4X)max
Round corner
b
BOTTOM VIEW
Detail "B"
C
A
S
Detail “A”
SIDE VIEW
A1
A2
Detail “B”
Dimensions in millimeters
Symbols
A
A1
A2
b
C
D
D1
E
E1
e
L
S
Min.
0.65
0.000
0.154
0.18
2.95
2.95
0.45
0.30
Nom.
0.75
0.025
0.203
0.23
0.3 Ref.
3.00
1.7 Ref.
3.00
1.7 Ref.
0.50
0.40
0.25 Ref
Max.
0.85
0.050
0.280
0.30
3.05
3.05
0.55
0.50
Dimensions in inches
Symbols
A
A1
A2
b
C
D
D1
E
E1
e
L
S
Min.
0.026
0.000
0.006
0.007
Nom. Max.
0.030 0.033
0.001 0.002
0.008 0.011
0.009 0.012
0.012 Ref.
0.116 0.118 0.120
0.067 Ref.
0.116 0.118 0.120
0.067 Ref.
0.018 0.020 0.022
0.012 0.016 0.020
0.010 Ref.
Note:
1. Controlling dimension is millimeter, converted inch dimensions are not necessarily exact.
Rev. 1.2 June 2013
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Page 13 of 15
AOZ1935
Tape and Reel Dimensions, QFN-16 3mm x 3mm x 0.75mm
Carrier Tape
D0
D1
P1
E1
K0
E2
E
B0
T
P2
A0
P0
Feeding Direction
UNIT: mm
Package
DFN 3x3 EP
A0
3.40
±0.10
B0
K0
3.35
±0.10
1.10
±0.10
D0
1.50
+0.10/-0
D1
E
E1
E2
P0
P1
P2
T
1.50
+0.10/-0
12.00
±0.30
1.75
±0.10
5.50
±0.05
8.00
±0.10
4.00
±0.10
2.00
±0.05
0.30
±0.05
Reel
W1
S
G
N
M
K
V
R
H
W
UNIT: mm
Tape Size
Reel Size
M
N
W
W1
H
K
S
G
R
V
12mm
ø330
ø330.0
±0.50
ø97.00
±0.10
13.00
±0.30
17.40
±1.00
ø13.0
+0.50/-0.20
10.60
2.00
±0.50
—
—
—
Leader/Trailer and Orientation
Trailer Tape
300mm min.
Rev. 1.2 June 2013
Components Tape
Orientation in Pocket
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Leader Tape
500mm min.
Page 14 of 15
AOZ1935
Part Marking
AOZ1935QI
(3 x 3 QFN-16)
Assembly Lot Code
Part Number Code
I 0 8 W
Week Code & Year Code
Extension Code
Option Code
Assembly Location Code
LEGAL DISCLAIMER
Alpha and Omega Semiconductor makes no representations or warranties with respect to the accuracy or
completeness of the information provided herein and takes no liabilities for the consequences of use of such
information or any product described herein. Alpha and Omega Semiconductor reserves the right to make changes
to such information at any time without further notice. This document does not constitute the grant of any intellectual
property rights or representation of non-infringement of any third party’s intellectual property rights.
LIFE SUPPORT POLICY
ALPHA AND OMEGA SEMICONDUCTOR PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL
COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS.
As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant into
the body or (b) support or sustain life, and (c) whose
failure to perform when properly used in accordance
with instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of
the user.
Rev. 1.2 June 2013
2. A critical component in any component of a life
support, device, or system whose failure to perform can
be reasonably expected to cause the failure of the life
support device or system, or to affect its safety or
effectiveness.
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Page 15 of 15