Linear Technology DC1409 Manuale utente

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1409

LTC3788

DESCRIPTION

Demonstration circuit DC1409 is DC/DC boost

converter featuring the LTC3788 constant fre-

quency current mode boost controller. The

DC1409A operates over 5V to 24V input and pro-

vides 8A to 10A of output current at 12V output.

Also, the DC1409A provides a second 24V output

capable of delivering 3A to 5A. The 300kHz con-

stant frequency operation results in small and effi-

cient circuit. The converter provides high output

voltage accuracy (typically ±3%) over wide load

range with no minimum load requirement.

The demonstration circuit can be easily modified

to generate different output voltages. Also, the two

outputs can be connected together to generate

single output with two phase operation. Please

consult LTC factory for details.

The DC1409 has small circuit footprint. It is a high

performance and cost effective solution for Tele-

com, Automotive and Power Over Ethernet appli-

cations.

Design files for this circuit board are available.

Call the LTC factory.

PowerPath is a trademark of Linear Technology Corporation

Table 1. Performance Summary

PARAMETER CONDITION VALUE

Minimum Input Voltage DC1409A-A IOUT1 = 0A to 3A,

IOUT2 = 0A to 8A

Maximum Input Voltage IOUT1 = 0A to 5A

IOUT2 = 0A to 10A

24V

VOUT1

VOUT2

VIN = 5V to 24V, IOUT1 = 3A

VIN = 5V to 12V, IOUT2 = 8A

24V ±3%

12V ±3% (see text)

Typical Output Ripple VOUT1

VOUT2

VIN = 6V, IOUT = 3A

VIN = 12V, IOUT = 8A

200mVP–P

Nominal Switching Frequency 350kHz

QUICK START PROCEDURE

Demonstration circuit DC1409 is easy to set up to

evaluate the performance of the LTC3788. For

proper measurement equipment setup refer to

Figure 1 and follow the procedure below:

NOTE:

When measuring the input or output voltage

ripple, care must be taken to minimize the length

of oscilloscope probe ground lead. Measure the

input or output voltage ripple by connecting the

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1409

probe tip directly across the VIN or VOUT and

GND terminals as shown in Figure 2.

With power off, connect the input power supply

to Vin and GND.

Check the Vcc Bias voltage-setting jumper JP5.

Move it into Vin position if required.

Turn the input power source on and slowly in-

crease the input voltage. Be careful not to ex-

ceed 24V.

NOTE:

Make sure that the input voltage Vin

does not exceed 24V. If higher operating volt-

age is required, power components with higher

voltage ratings should be used.

Set the input voltage to 6V and check for the

proper output voltage of 12V and 24V.

If there is no output, temporarily disconnect the

load to make sure that the load is not set too

high.

Once the proper output voltage is established,

adjust the load and observe the output voltage

regulation, ripple voltage, efficiency and other

parameters.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1409

Figure 1. Proper Measurement Equipment Setup

VIN

GND

Figure 2. Measuring Input or Output Ripple

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1409

CHANGING THE OUTPUT VOLTAGE

To set the output voltage lower than 12V or 24V, change the bottom voltage divider resistors con-

nected to LTC3788 FB pin (see the schematic on page 6).

To get higher than 12V and 24V output voltages MOSFETs and capacitors with higher voltage rat-

ings may be required. Please contact LTC factory for details.

Note that the output voltage will start following the input voltage when input voltage is greater than

the voltage set by the voltage divider. In this mode (wire mode) the output rectifier MOSFET is

turned continuously ON. The only losses in this mode are due to the current sense resistors, induc-

tor and output MOSFET DC resistance.

CONVERTER EFFICIENCY AND OUTPUT CURRENT

The DC1409 output current capability depends on the input voltage and proper cooling. Typical per-

formance of DC1409A is shown in Figure 3. As can be seen from Figure 3, the output current ca-

pability depends on the input voltage. Also, when input voltage is equal or higher than the output

voltge setting (wire mode) the efficiency is very high (99%) since the converter is not really running

and the output MOSFET is shorting Vin to Vout (blue trace in Figure 3).

LTC3788 Efficiency 12V and 24V output

89%

91%

93%

95%

97%

99%

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Iout [A]

Efficiency

5V in, 24V out

12V in, 24V out

5V in, 12V out

12V in, 12V out

Figure 3. DC1409A Efficiency

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1409

OUTPUT LOAD STEP RESPONSE

The load step response of DC1409A is very good even though relatively small amount of output

capacitance is present at the output. If higher load steps need to be handled more output capaci-

tance can be added in order to keep the voltage transients at the desired level. The load step tran-

sients are shown in Figure 5 and Figure 6. Also, note that load step response even from 0% load is

excellent thanks to synchronous rectification.

Figure 5. 12V Output load step response

Figure 6. 24V Output load step response

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1409

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DC1409A

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