EPC EPC9144 Manual de início rápido - Página 3

Procurar online ou descarregar pdf Manual de início rápido para Placa-mãe EPC EPC9144. EPC EPC9144 9 páginas. Development board for a 15 v high current pulsed laser diode driver

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QUICK START GUIDE

OPERATING PRINCIPLE

THE EPC9144 is intended as both a demonstration board and a flexible

development platform. It is functional out of the box, but is designed

to be easily modified to accommodate a broad range of applications.

It is highly recommended that the user read the entire guide, but

especially the section MODIFICATIONS, in order to get maximum

value from the EPC9144.

The EPC9144 is shipped as a rectangular pulse laser diode driver. Please

refer to the block diagram (Fig. 2) and the schematics (Figures 7 & 8).

It has several possible modifications (section MODIFICATIONS), but only

the basic operation will be covered in this section. The EPC9144 basic

operating principle is to act as a current gate to allow current from the

voltage bus to flow through the laser diode or other load when the FET

Q1 is turned on, and stop the load current when the Q1 is turned off.

The speed of the driver and FET means that turn-on and turn-off can be

accomplished as fast as 500 ps and 250 ps, respectively, even for load

currents of approximately 10 A.

The FET Q1 is controlled via an input pulse that is delivered to MMCX

connector J5, which is terminated on the demo board with 50 Ω. J5 is

followed by a logic level translator. As shipped, the level translator is set

for 3.3 V logic levels, but the EPC9144 may be modified to accommodate

other logic levels (See MODIFICATIONS for further details).

After the level translator, the input pulse goes through a narrow pulse

generator circuit. The input pulse should be set > 10 ns longer than the

desired output pulse. As shipped, the pulse width is set to approximately

5 ns, but it may be adjusted to values in the range of 1.2 ns to 20 ns via

trimpot P1, with the lower limit determined by the LMG1020 gate driver IC.

Please note that it is possible to reduce the adjust the input pulse to a

value below the minimum pulse width capability of the LMG1020 gate

driver. In this case, the output will fail to function properly, and the P1

adjustment must be increased. Finally, in the case where one wishes to

control the pulse width externally via the input pulse, the narrow pulse

generator may be bypassed as discussed in the section MODIFICATIONS.

When the input goes high, the gate driver turns on Q1, allowing current

flow through the laser diode or load U2. After the narrow pulse generator

output goes low, Q1 turns off. If there is current remaining in the power

loop inductance, diode-connected EPC2036 FET Q2 can conduct and

help prevent overvoltage of the laser and FET.

The voltage bus for the laser diode or other load is bypassed via the

capacitor bank {C22, C23, C24, C25}. This capacitor bank is part of the

main power loop inductance, and the layout is designed to minimize

the effect of resulting parasitic inductance. The capacitor bank is fed

through a relatively small resistance formed by {R10, R11, R12, R13}.

The resistance served to limit the laser or load current continuous value

in the case of long pulses, and also serves to damp parasitic resonance

of the power loop.

Measurements of key waveforms can be made through the MMCX test

points provided. These test points can provide waveform measurements

with equivalent bandwidths > 3 GHz. As a result, they have requirements

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Signal generator

Signal Generator

Pulse width

adjust

Figure 2: Connection and measurement setup

Figure 3: Output terminals of the EPC9144

and properties that differ from most conventional oscilloscope

probes. More details on the usage of these test points is provided in

section MEASUREMENT CONSIDERATIONS.

LASER DIODE OR LOAD CONSIDERATIONS

The EPC9144 can be used as is to mount a laser diode or other load.

Figure 3 highlights the output pad locations. However, many laser

suppliers have different mounting footprints, making it difficult to

optimize the performance of the driver and still maintain the desired

flexibility. The use of an interposer PCB provides a solution to this

problem with a small added performance penalty in the form of an

additional 50 pH to 100 pH power loop inductance. The EPC9144 ships

with the EPC9989 interposer PCB, shown in Fig. 4. The EPC9989 has

an assortment of 5 mm square interposer PCBs that can be snapped

off the board. These interposers have various footprints on the top

side that can accommodate several surface mount laser diodes, an

MMCX connector, and several patterns designed to accommodate a

wide variety of possible loads. These interposers mount between the

EPC9144 and the laser diode or other load. The EPC9989 is updated

as new lasers or loads become available, so Fig. 4 may not show the

latest board.

Demonstration System EPC9144

VBUS

BUS

– +

–

Note

Note polarity

Polarity

Laser anode

Laser cathode

(FET drain)

GND (for alternate

applications)

Laser

diode

or load

Oscilloscope

(50 inputs)

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