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## TSM1051 Datasheet(PDF) 6 Page - STMicroelectronics

 Part No. TSM1051 Description CONSTANT VOLTAGE AND CONSTANT CURRENT CONTROLLER FOR BATTERY CHARGERS AND ADAPTORS Download 9 Pages Scroll/Zoom 100% Maker STMICROELECTRONICS [STMicroelectronics] Homepage http://www.st.com Logo

## TSM1051 Datasheet(HTML) 6 Page - STMicroelectronics

 6 / 9 page 6/91. Voltage and Current Control1.1. Voltage ControlThe voltage loop is controlled via a first transcon-ductance operational amplifier, the resistor bridgeR1, R2, and the optocoupler which is directly con-nected to the output.The relation between the values of R1 and R2should be chosen as written in Equation 1.R1 = R2 x Vref / (Vout - Vref)Eq1Where Vout is the desired output voltage.To avoid the discharge of the load, the resistorbridge R1, R2 should be highly resistive. For thistype of application, a total value of 100KΩ (ormore) would be appropriate for the resistors R1and R2.As an example, with R2 = 100KΩ, Vout = 4.10V,Vref = 1.210V, then R1 = 41.9KΩ.Note that if the low drop diode should be insertedbetween the load and the voltage regulation resis-tor bridge to avoid current flowing from the loadthrough the resistor bridge, this drop should betaken into account in the above calculations by re-placing Vout by (Vout + Vdrop).1.2. Current ControlThe current loop is controlled via the secondtrans-conductanceoperationalamplifier,thesense resistor Rsense, and the optocoupler.The control equation verifies:Rsense x Ilim = Vsenseeq2Rsense = Vsense / Ilimeq2’where Ilim is the desired limited current, andVsense is the threshold voltage for the currentcontrol loop.As an example, with Ilim = 1A, Vsense = -200mV,then Rsense = 200mΩ.Note that the Rsense resistor should be chosentaking into account the maximum dissipation(Plim) through it during full load operation.Plim = Vsense x Ilim.eq3As an example, with Ilim = 1A, and Vsense =200mV, Plim = 200mW.Therefore, for most adapter and battery chargerapplications, a quarter-watt, or half-watt resistor tomake the current sensing function is sufficient.Vsense threshold is achieved internally by a re-sistor bridge tied to the Vref voltage reference. Itsmiddle point is tied to the positive input of the cur-rent control operational amplifier, and its foot is tobe connected to lower potential point of the senseresistor as shown on the following figure. The re-sistors of this bridge are matched to provide thebest precision possible.The current sinking outputs of the two trans-con-ductance operational amplifiers are common (tothe output of the IC). This makes an ORing func-tion which ensures that whenever the current orthe voltage reaches too high values, the optocou-pler is activated.The relation between the controlled current andthe controlled output voltage can be describedwith a square characteristic as shown in the fol-lowing V/I output-power graph.Figure 9 : Output voltage versus output current2. CompensationThe voltage-control trans-conductance operation-al amplifier can be fully compensated. Both of itsoutput and negative input are directly accessiblefor external compensation components.An example of a suitable compensation network isshown in Fig.2. It consists of a capacitorCvc1=2.2nF and a resistor Rcv1=470KΩ in series,VoutIoutVoltage regulationTSM1051 Vcc : independent power supply0Secondary current regulationTSM1051 Vcc : On power outputPrimary current regulationTSM1051PRINCIPLE OF OPERATION AND APPLICATION HINTS

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