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PDF AS3492 Data sheet ( Hoja de datos )
| Número de pieza | AS3492 | |
| Descripción | Highly Efficient 2-10 LEDs Backlight Driver | |
| Fabricantes | ams | |
| Logotipo |  |
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Datasheet
AS3492
Highly Efficient 2-10 LEDs Backlight Driver with 2 PWM Inputs
1 General Description
The AS3492 is an inductive highly efficient DCDC boost
converter. The DCDC converter operates at a fixed fre-
quency of 2MHz and includes soft startup to allow easy
integration into noise sensitive RF systems. A predict-
able startup is guaranteed even with very low duty cycle
PWM input signals. The voltage on the output capacitor
is controlled to minimize ripple and to avoid any acoustic
effects for low frequency PWM input signals.
The output of the DCDC converter is used for five cur-
rent sources connected to up to 10 LEDs. If a current
source is not required, it shall be connected to VOUT or
GND - the AS3492 detects this condition and disables
this current source automatically; this keeps the effi-
ciency of the system constantly high.
The AS3492 is controlled by two enable inputs, ON13
and ON45. These inputs can also be used to connect a
PWM input (like DLS or DBC).
The AS3492 includes several protection functions like
undervoltage lockout, overcurrent and overtemperature.
No microvias are required to assemble the AS3492 if
only four channels are used and ON13=ON45.
The AS3492 is available in a space-saving WL-CSP
package measuring only 1.7x1.4x0.5mm and operates
over the -30ºC to +85ºC temperature range.
Figure 1. AS3492 Typical Operating Circuit
2 Key Features
2 MHz DCDC Boost converter
- Small 4.7µH external coil
- Very high system efficiency of 86% (DCDC and
current sources combined)
- Very low voltage changes on output to avoid
acoustic noise on output capacitor even with PWM
- Smooth startup even under low duty cycle PWM
conditions
Five Current sources up to 25mA
- Low voltage compliance (150mV)
- High side current source to simplify layout and
thermal management of the LEDs
- Automatically detect and disable failing or not used
LEDs to keep efficiency high
- Current matching <4%
- Current accuracy <7.5%
Excellent LED current output ripple <500µA
Support DLS (Dynamic Luminance Scaling or DBC)
Undervoltage lockout and overcurrent protection
Overtemperature protection
Available in a tiny WL-CSP package
- 3x4 balls, 0.4mm pitch, 1.7x1.4x0.5mm
3 Applications
Display backlight driver for mobile phones, digital cam-
eras, PND and PMPs.
AS3492
www.austriamicrosystems.com/AS3492
(ptr)
1.2
1 - 18
1 page  
AS3492
Datasheet - Electrical Characteristics
Table 3. Electrical Characteristics (Continued)
Symbol
Parameter
ILED1..5
MATCH
LED1...LED5 current
source matching
Condition
ILED1..5 = 20mA
Min Typ
-4.0
ILED1..5
RIPPLE
LED1...LED5 ripple
current
BW=10MHz
ILED > 5mA
ILED < 5mA
ILED1..5
PWMLIN
LED1...LED5
linearity2
ILED=20mA,
PWM frequency 300Hz
PWM>=25/255
25/255>
PWM>=1/255
-2
-10
fPWM PWM input frequency
on pin ON13 or ON45
100
ILED1..5 LED1...LED5 leakage
LEAKAGE
current
current source off, TAMB < +50ºC
-0.5
LED1...LED5 current
VILED_COMP
source voltage
compliance
Minimum voltage between pin VOUT and
LED1...LED5, ILED<20mA3
100
Current Reference (pin ISET)
VISET
ISET voltage
ILED2ISET
LED current to
ISETcurrent
Protection Functions (see page 12)
VVOUT_MAX
VOUT overvoltage
protection
8.6
VVOUT_OPE VOUT open LED
NLED
detection threshold
Voltage level on VOUT where open LED
detection is performed
8.0
VLED_OPEN
VVLED1..5 open
detection
an open LED is assumed if the voltage on the
current source is less than VLED_OPEN and
VOUT=VVOUT_OPENLED
VLED_SHORT
VLED1..5 short
detection
voltage on LED1..5 where a shorted LED is
assumed
tLED_ERROR
_DEB_OPEN
VLED1..5 open
debounce time
Open LED detection debounce time
tLED_ERROR
_DEB_SHORT
VLED1..5 short
debounce time
Short LED detection debounce time4
ILIMIT
Current Limit for coil
LSW (Pin SW)
510
TOVTEMP
TOVTEMPHY
ST
Overtemperature
Protection
Overtemperature
Hysteresis
Junction temperature
VUVLO Undervoltage Lockout
Falling VVIN
Rising VVIN
1.8
VUVLO
+0.05
Digital Interface
VIH
High Level Input
Voltage
1.07
VIL
Low Level Input
Voltage
0.0
RPULLDOWN Pulldown resistor
1.8V on pad 90
300
0
1.25
400
8.5
92
0.95
600
144
5
1.9
2.2
250
Max
+4.0
10
500
+2
+10
800
+0.5
10.0
8.8
125
4.8
9.0
685
2.1
2.3
VVIN
0.68
Unit
%
% of
ILED
µA
%
%
Hz
µA
mV
V
A/A
V
V
mV
V
µs
µs
mA
ºC
ºC
V
V
V
V
k
1. Excluding variation of external resistor RISET; voltage difference between any set of drivers less than 200mV
www.austriamicrosystems.com/AS3492
1.2
5 - 18
5 Page 
AS3492
Datasheet - Detailed Description
Startup
In order to avoid inrush-current during startup the supplies are smoothly ramped up according to Figure 17 even under
low PWM duty cycle conditions. This allows the easy integration into mobile battery powered systems:
Figure 17. Startup Procedure
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Open and short LED detection
After the startup is finished, the AS3492 continuously monitors open and shorted LEDs. If an open or shorted LED
string is detected, this LED string is disabled and the driver continuous its normal operation. The driver is disabled to
keep the efficiency of AS3492 for different LED configurations high. The error is cleared once the AS3492 enters shut-
down4.
Shorted LED
After startup is finished, for any LED, enabled by the inputs ON13 or ON45, is below VLED_SHORT, for at least
tLED_ERROR_DEB_SHORT, a shorted LED is assumed.
Open LED
LED outputs (LED1...LED5) which are not used by the application shall be connected permanently to VOUT or GND.
The AS3492 detect this condition upon startup and automatically disables the current sources for these LEDs - see
Figure 18 and Figure 19, immediately after the rising edged of ON13 or ON45.
For LEDs, which are open during operation of the device, following procedure of the AS3492 is used for detection:
After startup is finished, if the voltage on VOUT=VVOUT_OPENLED5and the voltage across any current source, enabled
by the inputs ON13 or ON45, is below VLED_OPEN (VOUT-LED1...5), for at least tLED_ERROR_DEB_OPEN, an open LED
is assumed.
Figure 18 shows the waveform for the detection of a single open LED, Figure 19 for all LEDs open.
4. The error is automatically cleared as the open/short LED error might be temporarily (e.g. bouncing of the
connections to the LED)
5. If the current limit of the coil (ILIMIT) is reached before VOUT=VVOUT_OPENLED, an open LED is not
detected.
www.austriamicrosystems.com/AS3492
1.2
11 - 18
11 Page | ||
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| PDF Descargar | [ Datasheet AS3492.PDF ] | |
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