DEMOTSM108

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 this 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 available on the PCB in order to make it adaptable to a wide range of converter output power. In a first step, this application note will describe the typical application. 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 1/5 AN1695 - APPLICATION NOTE Figure 2 : Typical application schematic Q4-B R8 Vin Vout R17 L1 R18 C4 Q4-A C7 R19 R9 U1 14 GD 200mV 1 VCC VS ICTRL 2 4 5 !STBY UV OV UV/OV/!STBY ICOMP VCOMP VCTRL VREF 2,52V TSM108 7 OSC 3 GND 6 13 12 R7 C3 R6 C2 9 8 11 10 R10 C10 G C1 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 are 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 material Reference U1 Q4 L1 L C1 C2-C3 C4-C7 C10 R8-R17-R18-R19 R6-R7 R9 R10 R16-R22 2/5 Value TSM108ID STS3DPFS30 P0250.154T short circuit 220pF 22nF 47µF-25V 100nF 1Ω 22kΩ-10% 15kΩ-1% 11kΩ-1% short circuit Description PWM controller Mosfet + diode 150µH - buck main inductor filtering inductor oscillator capacitor compensation capacitors buck input and output capacitors voltage reference bias capacitor shunt resistor compensation resistors divider bridge upper resistor divider bridge lower resistor Manufacturer STMicroelectronics STMicroelectronics Pulse Rubycon ZL AN1695 - APPLICATION NOTE 2.2 Performances As explained in the datasheet, the step-down converter using TSM108 can feature an accurate constant-voltage and constant-current regulation. The V/I output characteristics of the DC/DC converter is shown in Figure 4. Input voltage was set at 12V during this test. As explained in introduction, voltage regulation is set to 6V and current regulation is set to 800mA. At output voltage lower than 1V, the foldback can be observed in the current regulation. Figure 4 : Output voltage versus output current characteristics 7 6 Vout (V) 5 4 3 2 1 0 0 100 200 300 400 500 600 700 800 900 Iout (mA) The efficiency of the DC/DC converter was measured in different conditions, as shown in Figure 5. On the left chart, the influence of output power (Pout) over efficiency is studied. It should be noted that during this test, the converter was operating in constant-voltage mode, therefore with Vout=6V and Iout