Linear Technology 1215 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1215

5A, 15V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR

LTC3605

DESCRIPTION

DESCRIPTIONDESCRIPTION

DESCRIPTION

Demonstration circuit 1215 is a step-down con-

verter, using the LTC3605 monolithic synchronous

buck regulator. The DC1215A has a maximum input

voltage 15V, and is capable of delivering up to 5A of

output current at a minimum input voltage of 4V.

The output voltage of the DC1215A can be set as

low as 0.6V, the reference voltage of the LTC3605.

At low load currents, the DC1215A operates in dis-

continuous mode, and during shutdown, it con-

sumes less than 10 uA of quiescent current. In

continuous mode operation, the DC1215A is a high

efficiency circuit - over 80%. The LTC3605 has

phase lock circuits, allowing high current multi-

phase operation of several DC1215As in parallel.

The DC1215A can also track another voltage with

the LTC3605 track function. Because of the high

switching frequency of the LTC3605, which is pro-

grammable up to 4 MHz, the DC1215A uses low

profile surface mount components. All these fea-

tures make the DC1215A an ideal circuit for use in

industrial applications and distributed power sys-

tems. Gerber files for this circuit are available.

Call the LTC Factory.

Design files for this circuit are available. Call

the LTC Factory

LTC is a trademark of Linear Technology Corporation

Table 1. Performance Summary (TA= 25°C)

PARAMETER CONDITIONS VALUE

Minimum Input Voltage 4V

Maximum Input Voltage 15V

GND = Shutdown

Run/Shutdown VIN = Run

VIN = 4V to 15V, IOUT = 0A to 5A 2.5V ±4% (2.4V – 2.6V)

VIN = 4.5V to 15V, IOUT = 0A to 5A 3.3V ±4% (3.168V – 3.432V)

Output Voltage VOUT Regulation

VIN = 6.4V to 15V, IOUT = 0A to 5A 5V ±4% (4.8V – 5.2V)

Typical Output Ripple VOUT VIN = 12V, VOUT = 2.5V, IOUT = 2.5A (20 MHz BW) < 40mVP–P

Discontinuous Mode VIN = 12V, VOUT = 2.5V < 2A

Nominal Switching Frequency RT= 162k 1 MHz

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1215

5A, 15V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR

QUICK START PROCEDUR

QUICK START PROCEDURQUICK START PROCEDUR

QUICK START PROCEDURE

Demonstration Circuit 1215 is easy to set up to evalu-

ate the performance of the LTC3605. For proper

measurement equipment configuration, set up the

circuit according to the diagram in Figure 1

Figure 1Figure 1

Figure 1. Before

proceeding to test, insert shunts into the OFF position

of the RUN header JP7, the forced continuous mode

position (FCM) of the MODE header JP6, the 2 phase

position of the PHMODE header JP5, and the 3.3V

output voltage header, JP2.

When measuring the input or output voltage ripple,

care must be taken to avoid a long ground lead on the

oscilloscope probe. Measure the input or output volt-

age ripple by touching the probe tip directly across

the Vin or Vout and GND terminals. See Figure 2

Figure 2Figure 2

Figure 2 for

proper scope probe measurement technique.

With the DC1215 set up according to the proper

measurement configuration and equipment in Figure

FigureFigure

Figure

1, apply 6.3V at Vin (Do not hot-plug Vin or increase

Vin over the rated maximum supply voltage of 15V, or

the part may be damaged.). Measure Vout; it should

read 0V. Turn on the circuit by inserting the shunt in

header JP7 into the ON position. The output voltage

should be regulating. Measure Vout - it should

measure 2.5V +/- 2% (2.45V to 2.55V).

Vary the input voltage from 4V to 15V and adjust the

load current from 0 to 5A. Vout should read 2.5V +/-

4% (2.4V to 2.6V).

Adjust the output current to 5A. Measure the output

ripple voltage; it will measure less than 40 mVAC.

Observe the voltage waveform at the switch node

(pins 16 thru 19). Verify the switching frequency is

between 800 kHz and 1.2 MHz (T = 1.25 us and 0.833

us), and that the switch node waveform is rectangular

in shape.

Change the JP6 shunt from forced continuous mode

to discontinuous mode (DCM). Also set the input

voltage to 12V and the output current to any current

less than 1.5A. Observe the discontinuous mode of

operation at the switch node, and measure the output

ripple voltage. It should measure less than 150 mV.

Insert the JP7 shunt into the OFF position and move

the shunt in the 2.5V output JP1 header into any of

the two remaining output voltage option headers:

3.3V (JP2) or 5V (JP3). Just as in the 2.5V Vout test,

the output voltage should read Vout +/- 2% tolerance

under static line and load conditions and +/- 1% tol-

erance under dynamic line and load conditions (+/-

2% total). Also, the circuit operation in discontinu-

ous mode will be the same.

When finished, turn off the circuit by inserting the

shunt in header JP7 into the OFF position.

Low Output Voltage Configuration

For applications with output voltages less than 2V, the

inductor value of 1 uH on the DC1215 should be

changed to 0.33 uH. This is required so that the in-

ductor ripple current ramp has a large enough slope

for the current comparator can distinguish it from

noise voltages.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1215

5A, 15V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR

Figure 1.

Figure 1.Figure 1.

Figure 1.

Proper Equipment Measurement Set

Proper Equipment Measurement SetProper Equipment Measurement Set

Proper Equipment Measurement Set-

-Up

UpUp

Figure 2.

Figure 2.Figure 2.

Figure 2. Measuring Input or Output Ri

Measuring Input or Output RiMeasuring Input or Output Ri

Measuring Input or Output Rip

pple

pleple

ple

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1215

5A, 15V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR

Normal Switching Frequency & Output Ripple Voltage

Normal Switching Frequency & Output Ripple VoltageNormal Switching Frequency & Output Ripple Voltage

Normal Switching Frequency & Output Ripple Voltage

Waveforms

WaveformsWaveforms

Waveforms

Figure 3.

Figure 3.Figure 3.

Figure 3. Switch Waveform & Output Ripple Voltage

Switch Waveform & Output Ripple VoltageSwitch Waveform & Output Ripple Voltage

Switch Waveform & Output Ripple Voltage

ININ

= 12

1212

12V, V

V, VV, V

V, V

OUT

OUTOUT

OUT

= 2.5

2.52.5

2.5V, I

V, IV, I

V, I

OUT

OUTOUT

OUT

= 5

A, Fsw = 1 MHz

, Fsw = 1 MHz, Fsw = 1 MHz

, Fsw = 1 MHz

Trace 3: Output Ripple Voltage (20 mV/div AC)

Trace 3: Output Ripple Voltage (20 mV/div AC)Trace 3: Output Ripple Voltage (20 mV/div AC)

Trace 3: Output Ripple Voltage (20 mV/div AC)

Trace 1: Switch Voltage (5 V/div)

Trace 1: Switch Voltage (5 V/div)Trace 1: Switch Voltage (5 V/div)

Trace 1: Switch Voltage (5 V/div)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1215

5A, 15V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR

Load Step Response Wav

Load Step Response WavLoad Step Response Wav

Load Step Response Wave

eform

formform

form

Figure 4.

Figure 4.Figure 4.

Figure 4. Load Step Response

Load Step ResponseLoad Step Response

Load Step Response

ININ

= 12V, V

= 12V, V= 12V, V

= 12V, V

OUT

OUTOUT

OUT

= 2.5V, 5A Load Step (0A <

= 2.5V, 5A Load Step (0A <= 2.5V, 5A Load Step (0A <

= 2.5V, 5A Load Step (0A <-

> 5A)

5A)5A)

5A)

Forced Continuous Mode

Forced Continuous ModeForced Continuous Mode

Forced Continuous Mode Fsw = 1 MHz

Fsw = 1 MHzFsw = 1 MHz

Fsw = 1 MHz

Trace 3: Output Voltage (100mV/di

Trace 3: Output Voltage (100mV/diTrace 3: Output Voltage (100mV/di

Trace 3: Output Voltage (100mV/div AC)

v AC)v AC)

v AC)

Trace 4: Output Current (2

Trace 4: Output Current (2Trace 4: Output Current (2

Trace 4: Output Current (2A/div)

A/div)A/div)

A/div)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1215

5A, 15V, MONOLITHIC SYNCHRONOUS STEP-DOWN REGULATOR

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