laboratory 12 - smps

Analog System Lab Kit PRO

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The goal of the experiment is to configure the on-board evaluation module TPS40200 on the ASLK PRO Kit as a switched mode power supply that can provide a regulated output voltage of 5V or 3.3V for an input whose range is 6V-15V.

The TPS40200 evaluation module included on ASLK PRO. Kit uses the TPS40200 non synchronous buck converter to provide a resistor-selected, 3.3V or 5V output that delivers up to 2.5A from up to 16V input bus. See Figure 12-1 for a schematic diagram of the EVM. The evaluation module operates from a single supply and uses the single

12.1 Brief theory and motivation

Goal of the experiment

Figure 12.1: Schematic of the on-board EVM

P–channel Power FET and Schottky diode to produce a low cost buck converter. The regulated output of the EVM is resistance-selected and can be adjusted within the limited range by making the changes in the feedback loop, as shown below.

The feedback factor

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VV

V V

R RR

V V duty cycle

TP

TP

M

R

TP

J

TP

TP

R

C

209 207

209

205

207

209

20

201

203

204

201

213

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=

=

=

b

b+

can be changed by changing feedback resistance R209 to adjust the output. But in ASLK PRO, we do not have the provision of changing R209. We can therefore achieve this task by connecting an external resistance of suitable value between the terminals TP8 and the ground.

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VV

V V

R RR

V V duty cycle

TP

TP

M

R

TP

J

TP

TP

R

C

209 207

209

205

207

209

20

201

203

204

201

213

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RC1

SS2

COMP3

FB4 GND 5

DRV 6

ISNS 7

VDD 8

TPS4

0200

RC

SS

COMP

FB

VDD

ISNS

DRV

GND

U4

4

3

6521

Q101FDC5614P

VIN

6 –

15V

VOU

T 3.

3V o

r 5V

VIN

VOUT

GATE

SRC

DR

AIN

RC

SS

COMP

FB

ISNS

DRV

DC/DC IN

HD143VOUT

R34K7

C20268pF

C203220nF

C204220nF

C205

470pF

C2064.7nF

C20733pF

C208100nF

C21110uF

C21210uF

C213470pF

C214470nF

C201220uF

C209330uF

C210330uF

L201

33uH

R201100K

R2020.03

R203

1K

R204

0E

R 205100K

R 20625.5E

R207

100K

R208

49.9

R20927K4

R2101M

R21141K2

HD120

TP2HD121TP3

HD122TP1

HD123TP8

HD124

TP6

HD125TP9

HD126TP4

HD127

TP7

HD128TP5

LD3

JP9

D201MBRS340

CN6

VOUT

CN5

VIN

JP8

VCC+10

@0.

125

– 2.

5A

3.3V

5V

HD142

Vin


The unregulated input is connected at screw terminal CN5. Output load is connected to screw terminal at CN6.The switching waveform can be observed at the terminal TP4.The evaluation module has a switching frequency of 200 kHz. This frequency is decided by the combination of R201 and C213. The duty cycle of this waveform varies linearly with the input voltage for a constant output voltage, as shown below.

What should be the value of the external resistance to be connected between TP8andGround to configure theevaluationmodule togenerate regulatedoutput voltage of 5V?

Simulatetheconfiguredcircuitusingasimulator.Thetypicalwaveformswillbe of the form shown in Figure 12.2.

In this experiment, we wish to study the line and load regulation for the TPS40200 integratedcircuitwhenitisconfiguredtogeneratea5VDCoutput.

Configuretheonboardevaluationmoduletogenerateconstant5VDCoutputbymaking the changes in the feedback path using the available terminals.

12.2Specifications

12.3 Measurements to be taken

12.4 What should you submit?

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Figure 12.2: Simulation waveforms - TP3 is the PWM waveform and TP4 is the switching waveform

The output ripple voltage can be measured across terminals TP5 and TP7 by simply placing the oscilloscope probes. The oscilloscope must be set for

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VV

V V

R RR

V V duty cycle

TP

TP

M

R

TP

J

TP

TP

R

C

209 207

209

205

207

209

20

201

203

204

201

213

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impedance, AC coupling. The same terminals can be used for the measurement of the regulated output DC voltage using a voltmeter.

What should be the value of the external resistance for the regulated output of 5V?

Obtain the Line Regulation: Vary the input voltage from 10V to 15V in steps of 0.5V and plot the output voltage as the function of the input voltage for a constant output load.

Obtain the Load Regulation: Vary the load (within the permissible limits) such that load current varies and obtain the output voltage for constant input voltage. Plot the output voltage as a function of the load current.

1

1

3

4

2

2

TP3

TP4

Vin

Vout

1.00

0.0020.00

-10.0010.00

10.005.01

4.98

10.00m 10.02m 10.05m 10.07m 10.10m

Configure the on board evaluationmodule to generate a regulated outputvoltage of 5V, and observe the waveforms mentioned in Figure 12.2 and compare with the simulation results.

Vary the input voltage for a regulated output voltage of 5V and observe the change in the duty cycle of the PWM waveform. Use Table 12.1 to record the readings. Compare the readings with simulation results and plot the graph between the input voltage and duty cycle. Is the plot linear?

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VV

V V

R RR

V V duty cycle

TP

TP

M

R

TP

J

TP

TP

R

C

209 207

209

205

207

209

20

201

203

204

201

213

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Varytheinputvoltageforafixedloadandobservetheoutputvoltage.UseTable 12.2 for taking the readings for line regulation

Vary the load so that load current varies; observe the output voltage for a fixedinputvoltage.UseTable12.3fortakingthereadings.

Table 12.1: Variation of the duty cycle of PWM waveform with input voltage

Table 12.2: Line regulation

Table 12.3: Load regulation

S.No. Input voltage (Vin) Duty cycle

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2

3

4

S.No. Input voltage (Vin) Output voltage (Vout)

1

2

3

4

S.No. Load current Output voltage (Vout)

1

2

3

4

5

6

Notes on Experiment 12:

laboratory 12 - smps

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