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PDF AT9919 Data sheet ( Hoja de datos )
| Número de pieza | AT9919 | |
| Descripción | High Brightness LED Driver | |
| Fabricantes | Supertex | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AT9919 (archivo pdf) en la parte inferior de esta página. Total 7 Páginas | ||
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Supertex inc.
AT9919
Hysteretic, Buck, High Brightness LED Driver
with High-Side Current Sensing
Features
►► Hysteretic control with high-side current sensing
►► Wide input voltage range: 4.5 to 40V
►► >90% Efficiency
►► Typical ±5% LED current accuracy
►► Up to 2.0MHz switching frequency
►► Adjustable constant LED current
►► Analog or PWM control signal for PWM dimming
►► Over-temperature protection
►► -40ºC to +125ºC operating temperature range
►► AEC-Q100 compliant
Applications
►► Automotive LED lighting applications
General Description
The AT9919 is a PWM controller IC designed to drive high
brightness LEDs using a buck topology. It operates from an
input voltage of 4.5 to 40VDC and employs hysteretic control
with a high-side current sense resistor to set the constant
output current.
The operating frequency range can be set by selecting the
proper inductor. Operation at high switching frequency is
possible since the hysteretic control maintains accuracy even
at high frequencies. This permits the use of small inductors
and capacitors minimizing space and cost in the overall
system.
LED brightness control is achieved with PWM dimming from
an analog or PWM input signal. Unique PWM circuitry allows
true constant color with a high dimming range. The dimming
frequency is programmed using a single external capacitor.
The AT9919 comes in a small, 8-Lead DFN package and is
qualified for automotive LED lighting applications.
Typical Application Circuit
CIN
RSENSE
L
0 - 2.0V
Doc.# DSFP-AT9919
A061212
CS VIN
RAMP
VDD
ADIM
GATE
DIM GND
AT9919
Supertex inc.
www.supertex.com
1 page  
AT9919
One possible application of the ADIM feature of the AT9919
may include protection of the LED load from over-tempera-
ture by connecting an NTC thermistor at ADIM, as shown in
Figure 1.
VDD
AT9919
ADIM
comparator with hysteresis (Figure 2). As the current through
the inductor ramps up and the voltage across the sense re-
sistor reaches the upper threshold, the voltage at GATE goes
low, turning off the external MOSFET. The MOSFET turns on
again when the inductor current ramps down through the
freewheeling diode until the voltage across the sense resis-
tor equals the lower threshold. Use the following equation to
determine the inductor value for a desired value of operating
frequency fS:
NTC
GND
L
=
(VIN - VOUT )VOUT
fSVIN∆IO
-
(VIN
-
VOUT
∆IO
)tDPDL
-
VOUT tDPDH
∆IO
Figure 1
Setting LED Current with External Resistor RSENSE
The output current in the LED is determined by the external
current sense resistor (RSENSE) connected between VIN and
CS. Disregarding the effect of the propagation delays, the
sense resistor can be calculated as:
RSENSE ≈
1
2
•
(VRS(HI) + VRS(LO)
ILED
)
=
200mV
ILED
Selecting Buck Inductor L
The AT9919 regulates the LED output current using an input
where:
∆IO
=
V - VRS(HI)
RS(LO)
RSENSE
and tDPDL, tDPDH are the propagation delays. Note, that the cur-
rent ripple ∆I in the inductor L is greater than ∆IO. This ripple
can be calculated from the following equation:
∆ I = ∆IO + (VIN - VLOU T)tDPDL
+
VOUTtDPDH
L
For the purpose of the proper inductor selection, note that
the maximum switching frequency occurs at the highest VIN
and VOUT = VIN/2.
VRS(HI)
RSENSE
ILED
VRS(LO)
RSENSE
tDPDL
TS
=
1
fS
tDPDH
ΔI
ΔIO
VDIM
t
Doc.# DSFP-AT9919
A061212
Figure 2
5
t
Supertex inc.
www.supertex.com
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet AT9919.PDF ] | |
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