Microchip AT9933DB1 Handleiding

Microchip Niet gecategoriseerd AT9933DB1

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Supertex inc.
Supertex inc.
www.supertex.com
AT9933DB1
Doc.# DSDB-AT9933DB1
A032713
General Description
The AT9933DB1 is an LED driver capable of driving up
to 7 1-watt LEDs in series from an automotive input of
9 - 16V DC. The demoboard uses Supertex’s AT9933
in a boost-buck topology. The converter operates at
frequencies in excess of 300kHz and has excellent output
current regulation over the input voltage range. It can also
withstand transients up to 42V and operate down to 6V
input. The converter is also protected against open LED
and output short circuit conditions. Protection against
reverse polarity up to 20V is also included.
Board Layout
High Bright LED Driver IC Demoboard
Meeting Automotive Requirements
Specications
Parameter Value
Input voltage (steady state): 9.0 - 16VDC
Input voltage (transient): 42VDC
Output LED string voltage: 28V max
Output current: 350mA +/-5%
Output current ripple: 5% typical
Switching frequency:
300kHz (9.0V input)
430kHz (13.5V input)
500kHz (16.0V input)
Efciency: 80% (at 13.5V input)
Open LED protection: Included; clamps
output voltage at 33V
Output short circuit protection: Included; limits current
at 350mA
Reverse polarity protection: -20V max
Input current limit: 1.9A
PWM dimming frequency: Up to 1.0kHz
Conducted EMI:
Meets SAE J1113
conducted EMI
standards
Connections:
Input:
The input is connected between the terminals of connector
J1 as shown in the Connection Diagram.
Output:
The output is connected between the terminals of connector
J2 as shown.
Enable/PWM Dimming:
To just enable the board, short pins 1 and 2 of connector J3
as shown. For PWM dimming, connect the external push-pull
square wave source between terminals 1 and 3 of connector
J3 as shown by the dotted lines.
Note:
During PWM dimming, pin 2 of connector J3 should be left
open. Also, the PWM signal must have the proper polarity
with the positive connected to pin 1 of J3. Note that pin 3
of J3 is internally connected to the return path of the input
voltage
Actual Size: 2.25” x 1.25”
2
AT9933DB1
Supertex inc.
www.supertex.com
Doc.# DSDB-AT9933DB1
A032713
Testing the Demoboard
Normal Operation: Connect the input source and the output
LEDs as shown in the Connection Diagram and enable the
board. The LEDs will glow with a steady intensity. Connect-
ing an Ammeter in series with the LEDs will allow measure-
ment of the LED current. The current will be 350mA +/- 5%.
Open LED test: Connect a voltmeter across the output ter-
minals of the AT9933DB1. Start the demoboard normally
and once the LED current reaches steady state, unplug one
end of the LED string from the demoboard. The output volt-
age will rise to about 33V and stabilize.
Short Circuit Test: When the AT9933DB1 is operating in
steady state, connect a jumper across the terminals of the
LED string. Notice that the switching frequency drops, but
the average output current remains the same.
PWM Dimming: With the input voltage to the board discon-
nected, apply a TTL compatible, push-pull square wave sig-
nal between PWMD and GND terminals of connector J3 as
shown in the Connection Diagram. Turn the input voltage
back on and adjust the duty cycle and / or frequency of the
PWM dimming signal. The output current will track the PWM
dimming signal. Note that although the converter operates
perfectly well at 1.0kHz PWM dimming frequency, the best
PWM dimming ratios can be obtained at lower frequencies
like 100 or 200Hz
Typical Results
Fig.1 shows the efciency plot for the AT9933DB1 over the
input voltage range. The converter has efciencies greater
than 80% over 13V input. Note that these measurements
so not include the 0.3 - 0.5W loss in the reverse blocking
diode.
Fig.2 shows the variation of the switching frequency over
the input votage range. The frequency varies from 300kHz
to 500kHz over the entire input voltage range and avoids
the restricted frequency band of 150 to 300kHz and the AM
band greater than 530kHz. This makes it easier to meet the
conducted and radiated EMI specications for the automo-
tive industry.
Fig.3 shows the output current variation over the input volt-
age range. The LED current has a variation of about 2mA
over the entire voltage range.
The waveforms in Fig.4 show the drain voltage of the FET
(channel 1 (blue); 10V/div) and the LED current (channel 4
(green); 100mA/div) at three different operating conditions
– 9V in, 13.5V in and 16V in.
Fig. 5 shows the operation of the converter during cold
crank conditions as the input voltage decreases from 13.5
to 6V and increases back to 13.5V. In these cases, the input
current reaches the limit set and the output current drops
correspondingly. Thus, the LEDs continue to glow, but with
reduced intensity. Once the voltage ramps back up, the out-
put current goes back to its normal value and the converter
comes out of the input current limit.
Fig.6 shows the LED current during an input step change
from 13.5 to 42V and back to 13.5V (similar to a clamped
load dump). It can be seen that the LED current drops briey
when the input voltage jumps, but there are no overshoots.
Fig. 7a shows the operation of the converter during an Open
LED condition and Fig. 7b shows the operation during output
short circuit condition. In both cases, it can be seen that the
AT9933DB1 can easily withstand faults and come back into
normal operation almost instantly.
Fig. 8 shows the PWM dimming performance of the
AT9933DB1 with a 100Hz, 3.3V square wave signal. The
converter can easily operate at PWM dimming duty cycles
from 1 - 99%.
Fig. 9 shows the rise and fall times of the output current dur-
ing PWM dimming. The converter has nearly symmetric rise
and fall times of about 25µs. These rise and fall times can
be reduced (if desired) by reducing the output capacitance
C10. However, this will lead to increased ripple in the output
current.
3
AT9933DB1
Supertex inc.
www.supertex.com
Doc.# DSDB-AT9933DB1
A032713
Fig. 1. Efficiency vs. Input Voltage
84
82
80
78
76
74
72
70
Input Voltage (V)
E ) ffi (%ciency
500
450
400
350
300
Input ltage (V) Vo
Switching Frequency (kHz)
Fig.2. Switching Frequency vs ag. Input Volt e
350.5
350.0
349.5
349.0
348.5
348.0
Input Voltage (V)
Output Current (mA)
Fig. 3. Output Current evs. Input Voltag
8.0 10 12 14 16 18
8.0 10 12 14 16 18
8.0 10 12 14 16 18

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: AT9933DB1

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