ST AN2448 APPLICATION NOTE

AN2448

Application note

EVALTSM1052: Ultra small battery charger using TSM1052

Introduction

This document describes a low power adapter that can be used in travel battery charger
applications. It uses the new Constant Voltage Constant Current (CVCC) controller
TSM1052, which is housed in one of the smallest packages available (SOT23-6L). Thanks
to its low consumption and low operating voltage, good electrical performance is achieved.
Another important feature of this SMPS is the absence of the Y1 safety capacitor between
primary and secondary grounds.

Figure 1. EVALTSM1052 demo board

July 2007 Rev 1 1/21

www.st.com

Contents AN2448

Contents

1 Adapter features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.1 Main characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Electrical behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Electrical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.2 Output characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3 Hold-up time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4 Conducted noise measurements (pre-compliance test) . . . . . . . . . . . 16

5 Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

6 BOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7 PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2/21

AN2448 List of figures

List of figures

Figure 1. EVALTSM1052 demo board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3. V
Figure 4. V

Figure 5. Maximum supply voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 6. Minimum supply voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 7. V
Figure 8. V
Figure 9. V
Figure 10. V

Figure 11. Efficiency vs. output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 12. Output characteristics at 115 V
Figure 13. Power down at 115 V
Figure 14. Power down at 230 V
Figure 15. CE peak measure at 115 V
Figure 16. CE peak measure at 230 V
Figure 17. V
Figure 18. V

Figure 19. THT components placing (top side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 20. SMT components placing (bottom side) and copper tracks. . . . . . . . . . . . . . . . . . . . . . . . 20

= 115 Vrms - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

in

= 230 Vrms - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

in

= 115 Vac - no-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

in

= 230 Vac - no-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

in

= 115 Vac - short circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

in

= 230 Vac - short circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

in

with CDC (cable drop compensation) . . . . . . . . . . . . . . 13

- 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

ac

- 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

ac

= 115 Vac - full load - bottom and top sides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

in

= 230 Vac - full load - bottom and top sides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

in

ac

and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

ac

and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

ac

3/21

Adapter features AN2448

1 Adapter features

1.1 Main characteristics

● Input:

–V

– f: 45 ~ 66 Hz

● Output:

–5.1Vdc ± 2%

– 600 mA

– Cable drop compensation (0.33 mV/mA)

● No-load:

– Pin below 0.3 W

● Short circuit: protected with nominal current regulation

● PCB type & size:

–CEM-1

– Single side 35 µm

– 48 x 18 mm

● Safety: according to EN60065

● EMI: according to EN55022 - class B

: 90 ~ 264 Vrms

in

4/21

AN2448 Adapter features

Figure 2. Electrical diagram

Vout

C9

D5

1N4148WS

1uF

IC1B

12

TR1C

EF12.6LP

TR1A

EF12.6LP

21

R1

330K

C4

1.5nF

250V

GND

5.1V - 600mA

R12

2.2K

R9

22K

1%

R7

5

4

6

Vs

C8

R14

SFH617-A3 X007

R6

330 Ohm

R5

100 Ohm

8 6

D2

UF108G

R2

680 Ohm

Vcc

4.7nF

Vctrl1Gnd2Out

IC3

3

22K

R13

220K

C7

22nF

R15

0 Ohm

C11

1.8nF

D4

STPS3L40S

IC2

VIPER12AS-E

8

S

D

7

S

D

6

D

5

D

FB

VDD

4

4

R10

10K

1%

R8

4.7K

C10

10nF

22K 1%

Ictrl

TSM1052

C6

16V

470µF

TR1D

EF12.6LP

1
2

3

R3 1K

3

IC1A

SFH617-A3 X007

C3

33µF

R11

0.33 Ohm

9 7

C5

330nF

50V

D3

1N4148WS

TR1B

EF12.6LP

R4

C2

4.7µF

400V

I1 1mHF1

C1

2.2µF

400V

3

2

10 Ohm 2W

AC1

1

-+

4

D1

S1ZB60

90÷264VAC

AC2

54

2.2 Ohm

5/21

Adapter features AN2448

1.2 Circuit description

The circuit used implements a flyback topology, which is ideal for a low power, low cost
isolated converter.

At primary side a VIPer12A-E has been used. This IC includes a current mode PWM
controller and a Power MOSFET in a small SO-8 package. The converter works in both
continuous and discontinuous conduction mode depending on the input voltage (the circuit
has a wide range input) and the output load. The switching frequency is internally fixed at 60
KHz. The design has been developed to reduce overall component count and adapter cost.

The input section includes a resistor for inrush current limiting, a diode bridge, two
electrolytic bulk capacitors and an inductor as front-end ac-dc converter and EMC filter. The
transformer is a layer type, uses a standard EF12.6 ferrite core and is designed to have a
reflected voltage of about 90 V. The peculiarity of this transformer is the winding technique
which allows the elimination of the usual Y1 safety capacitor between the primary and the
secondary. A RCD clamp network is used for leakage inductance demagnetization. The
power supply for the VIPer12A-E is obtained with a self supply winding from the transformer
connected in forward configuration. This circuit provides a voltage that is directly
proportional to the input rectified voltage and independent from the load voltage. In this way
even in short circuit condition (V
operating range (9 V to 38 V) of the VIPer12A-E allows a wide range mains input voltage.

At secondary side, the TSM1052 constant voltage constant current (CVCC) controller is
used. Like the VIPer12A-E, the TSM1052 is also supplied with a forward configuration, in
order to obtain the same benefit. The voltage is taken on one half of the secondary winding
(between pins 8 and 6), rectified with diode D5 and added to the output voltage. Under all
working conditions, the voltage supply for the TSM1052 and the photodiode IC1B is equal to
the output voltage plus forward rectified voltage on half secondary. With this configuration a
correct supply is provided over the whole input range, even with the output short circuited.

= 0), the IC is correctly supplied. The wide VDD

OUT

With this configuration a small ripple at twice line frequency is present at the output. This is
due to the supply of the photodiode IC1B, which is a replica of the voltage on C2. Usually
this is not a problem in battery chargers. There are two ways to eliminate this phenomenon
if necessary:

● C9 can be substituted by an electrolytic capacitor (at least 47 µF)

● The TSM1052 and IC1B can be attached directly to the output voltage. In this case the

current regulation is guaranteed only for output voltages down to 1.7 V

Resistor R7 has been added for cable drop compensation (the higher the output current the
higher the output voltage). R7 has been chosen according to the cable characteristics (it has
about 0.3 Ω of resistance).

6/21

AN2448 Electrical behavior

2 Electrical behavior

Figure 3 and Figure 4 show all the VIPer12A-E waveforms during normal operation at full

load. The converter operates in DCM at both 115 Vrms and 230 Vrms:

Figure 3. V

CH1: VIPer12A-E supply voltage (yellow)
CH2: VIPer12A-E feedback pin (red)
CH3: VIPer12A-E drain voltage (green)

= 115 Vrms - 60 Hz

in

7/21