Motore di ricerca datesheet componenti elettronici |
|
CS51221EDR16 Scheda tecnica(PDF) 8 Page - Cherry Semiconductor Corporation |
|
CS51221EDR16 Scheda tecnica(HTML) 8 Page - Cherry Semiconductor Corporation |
8 / 12 page Typical Performance Characteristics 8 Application Information: continued The VREF (ok) comparator monitors the 3.3V VREF output and latches a fault condition if VREF falls below 3.1V. The fault condition may also be triggered when the OV pin voltage rises above 2V or the UV pin voltage falls below 1V. The under-voltage comparator has a built-in hysteresis of 75mV (typ). The hysteresis for the OV comparator is programmable through a resistor connected to the OV pin. When an OV condition is detected, the over-voltage hys- teresis current of 12.5µA (typ) is sourced from the pin. In Fig.4, the fault condition is triggered by pulling the UV pin to the ground. Immediately, the SS capacitor is dis- charged with 5µA of current (typ) and the GATE output is disabled until the SS voltage reaches the discharge voltage of 0.3V (typ). The IC starts the Soft Start transition again if the fault condition has recovered as shown in Fig.4. However, if the fault condition persists, the SS voltage will stay at 0.10V until the removal of the fault condition. Figure 4: The fault condition is triggered when the UV pin voltage falls below 1V. The Soft Start capacitor is discharged and the GATE output is disabled. CH2: Envelop of GATE output, CH3: SS pin with 0.01µF capacitor, CH4: UV pin. Current Sense and Over Current Protection The current can be monitored by the ISENSE pin to achieve pulse by pulse current limit. Various techniques, such as a using current sense resistor or current transformer, can be adopted to derive current signals. The voltage of the ISET pin sets the threshold for maximum current. As shown in Fig. 5, when the ISENSE pin voltage exceeds the ISET voltage, the current limit comparator will reset the GATE latch flip- flop to terminate the GATE pulse. Figure 5: The GATE output is terminated when the ISENSE pin voltage reaches the threshold set by the ISET pin. CH2: ISENSE pin, CH4: ISETpin, CH3: GATE pin The current sense signal is prone to leading edge spikes caused by the switching transition. A RC low-pass filter is usually applied to the current signals to avoid premature triggering. However, the low pass filter will inevitably change the shape of the current pulse and also add cost. The CS51221uses leading edge blanking circuitry that blocks out the first 150ns (typ) of each current pulse. This removes the leading edge spikes without altering the cur- rent waveform. The blanking is disabled during Soft Start and when the VCOMP is saturated high so that the mini- mum on-time of the controller does not have the additional blanking period. The max SS detect comparator keeps the blanking function disabled until SS charges fully. The out- put of the max Duty Cycle detector goes high when the error amplifier output gets saturated high, indicating that the output voltage has fallen well below its regulation point and the power supply may be under load stress. Oscillator and Synchronization The switching frequency is programmable through a RC network connected to the RTCT Pin. As shown in Fig.6, when the RTCT pin reaches 2V, the capacitor is discharged by a 1mA current source and the Gate signal is disabled. When the RTCT pin decreases to 1V, the Gate output is turned on and the discharge current is removed to let the RTCT pin ramp up. This begins a new switching cycle. The CT charging time over the switch period sets the maximum duty cycle clamp which is programmable through the RT value as shown in the Design Guidelines. At the beginning of each switching cycle, the SYNC pin generates a 2.5V, 320nS (typ) pulse. This pulse can be utilized to synchronize other power supplies. |
Codice articolo simile - CS51221EDR16 |
|
Descrizione simile - CS51221EDR16 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEETIT.COM |
Lei ha avuto il aiuto da alldatasheet? [ DONATE ] |
Di alldatasheet | Richest di pubblicita | contatti | Privacy Policy | scambio Link | Ricerca produttore All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |