ST AN1695 Application note

AN1695

APPLICATION NOTE

TSM108 EVALUATION BOARD

12V to 6V DC/DC CONVERTER

by Anthony BOIMOND

1 - Introduction

The TSM108 is a step down controller that features constant voltage and constant current regulation. It can drive either a P-channel Mosfet or a PNP bipolar transistor. The principle of operation of the TSM108 is widely described in the application note attached to the datasheet. The goal of t his document is to describe the TSM108 Evaluation Board.

The Evaluation Board was designed to allow different converter configurations. Several options for power semiconductor footprints are avai lable on the PCB in order to make it adaptable to a wide range of converter output power. In a first step, this applicati on note will des cribe th e typical appli cation . Then the various options available on the Evaluation Board PCB will be explained.

2 - TSM108 typical application

2.1 Description

The TSM108 is especially suited for cigarette lighter accessories. The typical application described in this note is a battery charger with the following characteristics:

Input voltage: Vin = 12V Output voltage: Vout = 6V Maximum output current: Iout = 800mA A picture of the Evaluation Board in the typical application configuration is shown on Figure 1. The related

schematic is described on Figure 2.

Figure 1 : TSM108 Evaluation Board

January 2003

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AN1695 - APPLICATION NOTE

Figure 2 : Typical application schematic

Vin Vout

C4 C7

VCC

!STBY

TSM108

Q4-B

Q4-A

UV/OV/!STBY

OSC

GND

200mV

ICTRL

ICOMP

VCOMP

VCTRL

VREF

2,52V

C10

R8 R17 R18 R19

R10

The list of components used in the typical application board is shown in the bill of material here below. All other components are not mounted. Passive components like capacitors and resistors used in this Evaluation Board a re through-hole components to be more easily changed by the user. Of course, in real-life application, surface-mounted devices will be used and the whole application can fit into a very small PCB area.

Table 3 : Bill of mater ial

Reference Value Description Manufacturer

U1 TSM108ID PWM controller STMicroelectronics Q4 STS3DPFS30 Mosfet + diode STMicroelectronics

L1 P0250.154T 150µH - buck main inductor Pulse

L short circuit filtering inductor

C1 220pF oscillator capacitor C2-C3 22nF compensation capacitors C4-C7 47µF-25V buck input and output capacitors Rubycon ZL

C10 100nF voltage reference bias capacitor

R8-R17-R18-R19 1Ω shunt resistor

R6-R7 22kΩ-10% compensation resistors

R9 15kΩ-1% divider bridge upper resistor

R10 11kΩ-1% divider bridge lower resistor

R16-R22 short circuit

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