Abstract :UCC39421 / 2 is the highly efficient multi-mode high-frequency PWM controllers . This paper briefly introduces the UCC39421 / 2 of the features discussed in detail UCC39421 / 2 pin function theory and composition , given UCC9421 / 2 controller application methods and application circuit . Keywords :Multi-mode high-frequency PWM control of DC / DC transformation UCC39421 / 2 1 UCC39421 / 2 of the functional characteristics UCC39421 / 2 is an efficient low-power DC / DC converters. It is the work of a very wide power supply with high efficiency , and provides programming on reset function , the chip with a separate low-voltage detection comparator, while with pulse modulation , current limit and low current shutdown (5µA) function Can be widely used in cellular phones, pagers recorded , PDAs and other handheld devices. UCC39421 / 2 has the following features: * Use high efficiency single-ended primary inductance control boost , SEPIC or flyback (reverse boost ) topology, the input voltage can be higher or lower than the output voltage ; * Input voltage is low ( minimum 1.8V); * be able to drive external FETs for high current ; * with up to 2MHz oscillation frequency ; * can be synchronized ; * has a programmable frequency modes to optimize power and efficiency; * With pulse modulation limiting ; * low -power sleep mode supply current is 150µA, shutdown mode, supply current of only 5µA. Figure 1 UCC39421 / 2 structural block diagram Click to enlarge 2 constitutes a principle and pin functions 2.1 constitute the principle UCC39421 / 2 within the charge pump circuit , PWM oscillator, turn the control circuit , PWM circuit, current limit control circuit , low-power mode control circuit , the slope compensation circuit , PFM mode control circuit , error amplifier , low battery voltage comparator, Reset circuit , 1.24V reference source circuit and the comparator and logic circuits , etc., and its internal structure shown in Figure 1 . 2.2 Package and pin functions UCC39421 / 2 double- column 20/16 pin package , the pin arrangement shown in Figure 2 . The pin functions are as follows : COMP: error amplifier output . Application and to this end should be connected between the series compensation of a resistance-capacitance network ; CHRG: N -channel MOSFET gate driver output . This client application can be directly connected with the MOSFET gate ; CP: charge pump input. When using the charge pump when , CP capacitor connected with the pump ; do not use the charge pump circuit , CP access GND; FB: error amplifier feedback signal input. This client application is usually connected to the VOUT and GND resistor divider between the upper ; GND: Signal ground controller ; ISENSE: current sense amplifier input; LOWBAT: comparator input . Pin voltage higher than 1.25V when VDET , this end of the output is low ; f0 (MHz) = 50/RT (kO) SYNC / SD: synchronous / shutdown input . Their purpose is to control the switching frequency and internal clock frequency synchronization on or off the controller . VPUMP: charge pump output . Application status of this pin and connect a 1µF capacitor . VOUT: controller output pin ; VIN: power supply input pin . Application between this pin and GND with a 0.1µF to be decoupling capacitor ; VDET: Low battery voltage detection input terminal (UCC39421 no such pin ) . 3 Application 3.1 Topological Structure and the synchronous rectifier UCC39421 / 2 can be used to form the BOOST, Flyback and SEPIC topologies . At this point, the controller can be Vin = 1.8 ~ 8V to work . Applications according to the input voltage and output voltage select the appropriate topology type , Table 1 lists the UCC39421 / 2 of the VIN, VOUT and topological relationships. UCC39421 / 2 N sea can drive MOSFET, P -channel MOSFET can be driven synchronous rectifier . When RSEL pin connected to GND , RECT foot N -channel MOSFET can provide driving output signal; when RSEL feet and connected to VIN , RECT feet , compared with P -channel MOSFET to provide driver output signal. The topological type , VOUT and the relationship between the synchronous rectifier as shown in table 2 . 3.2 Typical Application Circuit Figure 3 shows a typical application circuit is the UCC39422 , the figure shows the connection of external components . For the UCC39421 , it compared with the UCC39422 , only one less independent low- battery voltage detection circuit reset circuit , the rest were the same. Circuit in Figure 3 , and the UCC39422 foot 11 (VDET) connected to the R1, R2 resistor divider consisting of the role is to detect low battery voltage . Figure 5 N -channel MOSFET synchronous use of integer charge pump converter with no input flyback converter Click to enlarge .3 Application Circuit boost transformation Figure 4 is the use of N -channel MOSFET for UCC39421 synchronous rectifier boost converter circuit . In Figure 4, the input voltage VIN of the range of 1.8V ~ 3.2V, output voltage Vout is 3.3V, which is listed in Table 1, line mode boost topology . RSENSE for the current sensing resistor , DPUMP, CFLY charge pump circuit consisting of the charging voltage can CFLY up to VOUT-VDIODE. CPUMP is the charge pump storage capacitors . 3.4 Application circuit flyback transform Figure 5 shows the use of N -channel MOSFET for UCC39421 synchronous rectifier , and does not take charge pump input flyback converter schematic . The figure , L1 first -class turns ratio of 1:1 . The advantages of this topology can be higher or lower than VOUT VIN.