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

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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

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AN2448	List of figures

List of figures

Figure 1. EVALTSM1052 demo board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3. Vin = 115 Vrms - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 4. Vin = 230 Vrms - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 5. Maximum supply voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

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

Figure 7. Vin = 115 Vac - no-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 8. Vin = 230 Vac - no-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 9. Vin = 115 Vac - short circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 10. Vin = 230 Vac - short circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 11. Efficiency vs. output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 12. Output characteristics at 115 Vac with CDC (cable drop compensation) . . . . . . . . . . . . . . 13

Figure 13. Power down at 115 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Figure 14. Power down at 230 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 15. CE peak measure at 115 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 16. CE peak measure at 230 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 17. Vin = 115 Vac - full load - bottom and top sides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 18. Vin = 230 Vac - full load - bottom and top sides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 19. THT components placing (top side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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

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Adapter features	AN2448

1 Adapter features

1.1Main characteristics

●Input:

–Vin: 90 ~ 264 Vrms

–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

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AN2448

.2 Figure

Electrical

1mH

diagram

10 Ohm 2W

AC1

Vout

1N4148WS

1uF

1.5nF

330K

TR1A

TR1C

IC1B

90÷264VAC

250V

EF12.6LP

S1ZB60

SFH617-A3 X007

2.2µF

4.7µF

400V

100 Ohm

22K

UF108G

680 Ohm

330 Ohm

R14

22K

4.7nF

AC2

C11

IC2

1.8nF

5.1V - 600mA

5 6 7 8

22nF

1N4148WS

VIPER12AS-E

STPS3L40S

IC3

D D D D

R15

Vcc

0 Ohm

Vctrl

R12

VDD

R13

2.2K

220K

Gnd

S S

TR1B

IC1A

Out

Ictrl

2 1

EF12.6LP

SFH617-A3 X007

TSM1052

22K 1%

470µF

TR1D

16V

EF12.6LP

33µF

50V

C10

330nF

10nF

R10

4.7K

10K

2.2 Ohm

GND

R11

0.33 Ohm

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features Adapter

Adapter features	AN2448

1.2Circuit 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 (VOUT = 0), the IC is correctly supplied. The wide VDD 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.

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 Ωof resistance).

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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. Vin = 115 Vrms - 60 Hz

CH1: VIPer12A-E supply voltage (yellow)

CH2: VIPer12A-E feedback pin (red)

CH3: VIPer12A-E drain voltage (green)

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