Microchip AT9933DB1 Manual

Microchip Ikke kategoriseret AT9933DB1

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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”

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.

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	AT9933DB1

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