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TPS61103RGER Datasheet(PDF) 5 Page - Texas Instruments |
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TPS61103RGER Datasheet(HTML) 5 Page - Texas Instruments |
5 / 35 page www.ti.com DETAILED DESCRIPTION SYNCHRONOUS RECTIFIER CONTROLLER CIRCUIT DEVICE ENABLE LDO ENABLE POWER GOOD TPS61100, TPS61103 TPS61106, TPS61107 SLVS411B – JUNE 2002 – REVISED APRIL 2004 The device integrates an N-channel and a P-channel MOSFET transistor to realize a synchronous rectifier. Because the commonly used discrete Schottky rectifier is replaced with a low RDS(ON) PMOS switch, the power conversion efficiency reaches 95%. To avoid ground shift due to the high currents in the NMOS switch, two separate ground pins are used. The reference for all control functions is the GND pin. The source of the NMOS switch is connected to PGND. Both grounds must be connected on the PCB at only one point close to the GND pin. A special circuit is applied to disconnect the load from the input during shutdown of the converter. In conventional synchronous rectifier circuits, the backgate diode of the high-side PMOS is forward biased in shutdown and allows current flowing from the battery to the output. This device however uses a special circuit which takes the cathode of the backgate diode of the high-side PMOS and disconnects it from the source when the regulator is not enabled (EN = low). The benefit of this feature for the system design engineer is that the battery is not depleted during shutdown of the converter. No additional components have to be added to the design to make sure that the battery is disconnected from the output of the converter. The controller circuit of the device is based on a fixed frequency multiple feedforward controller topology. Input voltage, output voltage, and voltage drop on the NMOS switch are monitored and forwarded to the regulator. So changes in the operating conditions of the converter directly affect the duty cycle and must not take the indirect and slow way through the control loop and the error amplifier. The control loop, determined by the error amplifier, only has to handle small signal errors. The input for it is the feedback voltage on the FB pin or, at fixed output voltage versions, the voltage on the internal resistor divider. It is compared with the internal reference voltage to generate an accurate and stable output voltage. The peak current of the NMOS switch is also sensed to limit the maximum current flowing through the switch and the inductor. The nominal peak current limit is set to 1500 mA. An internal temperature sensor prevents the device from getting overheated in case of excessive power dissipation. The device is put into operation when EN is set high. It is put into a shutdown mode when EN is set to GND. It also can be enabled with a low signal on ENPB. This forces the converter to start up as long as the low signal is applied. During this time EN must be set high to prevent the converter from going down into shutdown mode again. If EN is high, a negative signal on ENPB is ignored. In shutdown mode, the regulator stops switching, all internal control circuitry including the low-battery comparator is switched off, and the load is isolated from the input (as described in the synchronous rectifier section). This also means that the output voltage can drop below the input voltage during shutdown. During start-up of the converter, the duty cycle and the peak current are limited in order to avoid high peak currents drawn from the battery. An undervoltage lockout function prevents device start-up if the supply voltage on VBAT is lower than approximately 0.7 V. When in operation and the battery is being discharged, the device automatically enters the shutdown mode if the voltage on VBAT drops below approximately 0.7 V. This undervoltage lockout function is implemented in order to prevent the malfunctioning of the converter. When the voltage is applied at VBAT, the LDO can be separately enabled and disabled by using the LDOEN pin in the same way as the EN pin at the dc/dc converter stage described above. The PGOOD pin stays high impedance when the dc/dc converter delivers an output voltage within a defined voltage window. So it can be used to enable the converter after pushbutton start-up, or to enable any connected circuitry such as cascaded converters (LDO) or processor circuits. 5 Not Recommended for New Designs |
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