DTL2A Просмотр технического описания (PDF) - DATEL Data Acquisition products

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DTL2A

100 Watt, Digitally Programmable Serial-Input, Electronic Loads

DATEL Data Acquisition products  

DTL Series

100 WATT, SERIAL-INPUT ELECTRONIC LOADS

Initialization

Preparing the DTL2A to accept new digital data is accomplished by applying

logic "1's" to Control Strobe (CS, pin 7), Latch Data (LD, pin 4) and Clock

(CLK, pin 6) with all signals present and stable for a minimum of 1µsec.

During this interval, it does not matter whether or not data is present on the

Serial Data In (SDI, pin 5) line.

Serial Data

Following initialization, the 12-bit digital word representing the desired output

current is applied to the SDI pin. The serial data should appear starting with

the most significant bit (MSB, bit 1, D11) and ending with the least significant

bit (LSB, bit 12, D0). With each data bit present and stable on the SDI line,

the CLK must be toggled through a low-to-high transition to register that bit.

Twelve rising clock edges, at rates up to 500kHz, are required to clock all 12

digital bits into the DTL2A’s input register.

Latching Data and Presenting It to the D/A

After loading the LSB, the serial data word is latched by bringing the Control

Strobe (pin 7) high and then toggling the Latch Data pin (pin 4) through a

high-low-high sequence. Approximately 100µsec later, the output current will

settle to its final desired value.

Software: C Language

The following steps describe a typical timing sequence when using the

DTL2A’s 4 digital inputs and a programming language such as C. Using 4 bits

of a typical 8-bit port, assign BIT_0 to the Control Strobe (CS, pin 7), BIT_1

to Latch Data (LD, pin 4), BIT_2 to Serial Data In (SDI, pin 5), and BIT_3

to the Clock (CLK, pin 6).

1. Initialize with Control Strobe, Latch Data, and Clock high:

BIT_0 = 1, BIT_1 = 1, BIT_2 = X (don’t care), BIT_3 = 1

2. Bring the Control Strobe low.

BIT_0 = 0

3. Apply the MSB (D11) of the serial data word to Serial Data In.

BIT_2 = 0 or 1

4. Toggle the Clock high-low-high.

BIT_3 = 1 to 0 to 1

5. Apply D10 of the serial data word to Serial Data In.

BIT_2 = 0 or 1

6. Toggle the Clock high-low-high.

BIT_3 = 1 to 0 to 1

7. Repeat the process for remaining data bits D9 through D0.

8. Drive the Control Strobe high.

BIT_0 = 1

9. Toggle the Latch Data input high-low-high.

BIT_1 = 1 to 0 to 1.

Output Compliance Voltage and the Fault Line

For proper operation, the DTL2A’s output/load voltage must always be

between 2.5 and 50 Volts. The device cannot be used to directly load low-

voltage, e.g. 1.8V or 2.5V, power components or to simulate a true short

circuit (0 Volts). Voltages greater than 50V can damage the device. Voltages

<2.5V will result in insufficient biasing of the output current source and

consequently unpredictable or no operation. Accordingly, we have installed

an internal output/load-voltage monitoring circuit. If the output/load voltage

drops below 2.5V and the DTL2A’s output is at risk of becoming disabled,

the Fault line activates.

The Fault line is an optically isolated, active-low function with an open-

collector output (internal 10kΩ pull-up resistor to +5V). Under normal condi-

tions, its output is high (logic "1"). Under fault conditions (VOUT < 2.5V), its

output drops to a logic "0." There is no output/load-voltage monitoring circuit

for voltages greater than 50V, and operation above 50V can damage the

device.

An "offset supply" can be inserted between the DTL2A’s –Load output (pins

8 and 9) and the power device under test (DUT) to "translate" the DTL2A’s

47.5V output/load voltage range. The offset supply must have adequate

current capabilities and be connected with the polarities indicated in Figure 2

below. Under no circumstances should the voltage across the DTL2A’s output

be allowed to experience a polarity reversal.

If a 5V/20A offset supply is inserted as shown, the range of DUT voltages

will be –2.5 to +45 Volts. Such a configuration can be used for true short-

circuit testing. A mechanical relay can be used to short the outputs of the

DUT while the offset supply ensures the DTL2A always sees at least 5 Volts

across its outputs.

11

+LOAD

10

DTL2A

9

–LOAD

8

5V

–

+

+

DUT

–

SHORT

CIRCUIT

RELAY

Figure 2. An "Offset Supply" Enables

True Short-Circuit Testing

Thermal Considerations

The DTL2A can reliably handle 100W loads if its case temperature is

maintained at or below +50°C. With no heat sinking or auxiliary cooling, the

device can only handle loads up to 10 Watts. Please refer to the Temperature

Derating Curve for additional information. DATEL’s Electronic Load Applica-

tions Engineers can assist you in developing heat-sink solutions for your

higher-power DTL2A applications. Please contact us for details.

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