Linear Technology DC1345 User manual

DEMO CIRCUIT 1345

QUICK START GUIDE

WIDE INPUT VOLTAGE RANGE

NO RSENSE STEP-DOWN DC/DC CONVERTER

LTC3879EMSE

DESCRIPTION

Demonstration circuit 1345 is a wide input voltage

range, no Rsense step-down dc/dc converter featuring

the LTC3879EMSE. Its output voltage is 1.2V with a

load rating of 12A and the input voltage range is 4.5V

to 34V.

The fixed on-time valley current mode architecture of

the LTC3879EMSE provides a very fast load step re-

sponse. Other features of the board include a RUN pin,

a TRACK pin, a PGOOD pin and a MODE jumper to

select either CCM or DCM operation at light load.

Design files for this circuit board are available. Call

the LTC factory.

Table 1. Performance Summary (T

= 25°C)

PARAMETER CONDITION VALUE

Minimum Input Voltage 4.5V

Maximum Input Voltage 34V

Output Voltage V

OUT

= 4.5V to 34V, I

OUT

= 0A to 12A 1.2V ±2%

Maximum Output Current 12A

Typical Output Voltage Ripple V

= 12V, I

OUT

= 12A (20MHz BW) 20mV

P–P

Nominal Switching Frequency V

= 12V, I

OUT

= 12A 300kHz

Efficiency (see Figure 3 for efficiency curves) V

= 12V, I

OUT

= 12A 90% Typical

QUICK START PROCEDURE

Demonstration circuit 1345 is easy to set up to evalu-

ate the performance of the LTC3879EMSE. Refer to

Figure 1 for proper measurement equipment setup and

follow the procedure below:

NOTE:

When measuring the output voltage ripple, care

must be taken to avoid a long ground lead on the oscil-

loscope probe. See Figure 2 for proper scope probe

technique. Short, stiff leads should be soldered to the

(+) and (-) terminals of an output capacitor. The

probe’s ground ring needs to touch the (-) lead and the

probe tip needs to touch the (+) lead.

Place jumpers in the following positions:

RUN ON

MODE CCM

With power off, connect the input power supply to

Vin and GND.

Turn on the power at the input.

Check for the proper output voltages.

Vout = 1.176V to 1.224V

Once the proper output voltages are established,

adjust the loads within the operating range and ob-

serve the output voltage regulation, ripple voltage,

efficiency and other parameters.

DEMO CIRCUIT 1345

QUICK START GUIDE

Vin Load

Iout

Vout

Vin

supply

Iin

Figure 1.

Proper Measurement Equipment Setup

VOUT GND

COUT

Figure 2.

Measuring Output Voltage Ripple

DEMO CIRCUIT 1345

QUICK START GUIDE

Fsw = 300kHz, CCM

0 2 4 6 8 10 12 14

Load current (Amps)

Efficiency

Vin=5V

Vin=12V

Vin=24V

Vin=34V

Parameters:

QT = Infineon BSC093N04LSG

QB = Infineon BSC035N04LSG

L = Wurth 744325072

0.72uH, DCR=1.3mΩ+/- 10%

Ron = 576kΩ

Figure 3.

Typical Efficiency Curves

DEMO CIRCUIT 1345

QUICK START GUIDE

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