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BM1R00001-E2 Datasheet(PDF) 6 Page - Rohm |
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BM1R00001-E2 Datasheet(HTML) 6 Page - Rohm |
6 / 26 page 5/22 TSZ02201-0F4F0A2BM1R0-1-2 © 2016 ROHM Co., Ltd. All rights reserved. 20. Apr. 2016 Rev.002 www.rohm.com TSZ22111 • 15 • 001 BM1R00xxxF 0V -100mV -100mV MAX_TON TIMER -Vf Description of Block – continued 5. MAX_TON Block MAX_TON block sets the maximum ON time. DRAIN terminal voltage starts counting when the rising edge of the output voltage exceeds VCC × 1.4V (Typ). In addition, the recounting starts when it detects another rising edge. The synchronous rectification FET will be forced OFF after the set time has elapsed. The time can be adjusted by varying the resistance value of the resistor connected to the MAX_TON terminal. The relationship between the resistance value (RMAX_TON) and set time (TMAX_TON) is described as follows: Calculation Example: If you want to set the maximum ON time to 10µs, the value of RMAX_TON is as follows: However, the formula above is for an ideal approximation only; it is still strongly advised that the operation of the actual application should still be verified. By setting this time, it becomes possible to prevent the simultaneous ON operation of the primary side and the secondary side in continuous mode. The drive sequence in continuous mode operation is shown in the figure below: a capacitor C1 and a Moreover, in order to reduce as much as possible the influence of the switching noise, resistor R1 in series should be connected to the MAX_TON terminal. The capacitance should approximately be 1000pF, and the resistance value is recommended to be around 1kΩ.This also serves as phase compensation of MAX_TON terminal and therefore should be connected. This function may be disabled by pulling up the MAX_TON terminal to VCC pin in quasi-resonant and current resonance applications which do not operate on conti nuous mode. The 1000pF and 1kΩ resistor is also unnecessary. 6. AUTO SHUTDOWN Block The Auto Shutdown block automatically turns the synchronous rectification ON/OFF depending on the presence or absence of the DRAIN terminal pulse. Shutdown occurs if the input pulses on the DRAIN terminal has more than 200us between pulses. This stops the synchronous rectification operation. The IC will restart the synchronous rectification after it detects 256 occurrences of input pulses on the DRAIN terminal. 7. SHUNT REGULATOR Chip A high-accuracy shunt regulator with ultra-low consumption is used for controlling the output voltage of the AC/DC. Since the synchronous rectification and the shunt regulator are built in a completely different chip, GND separation is possible. Therefore, it becomes possible to place the shunt regulator on the secondary-side GND reference in the synchronous rectification applications in case of disposing the High Side FET. It can also be used as protection for the comparator, the secondary side OVP, FET overheat protection, etc. 8. PROTECTION Block When an abnormal condition is detected after the timer count is completed, the photo coupler from SH_OUT terminal is driven to stop the switching operation on the primary side. (1) Primary side FET = ON. Current I1 flows to the primary side FET. Secondary side drain voltage VDS2 rises. (2) The VDS2 = VCC × 1.4 detects the rise edge of the threshold, MAX_TON timer start. (3) Primary side FET = OFF. Current I2 flows through the Body Diode of the secondary side FET (OFF state). (4) Secondary side drain voltage VDS2<-100mV by I2 Current, Secondary side FET=ON. (5) Elapsed the set time in MAX_TON terminals, the secondary-side FET = compulsory OFF. (6) Since the I2 current flows through the Body Diode, Vf voltage occurs. k s k µs 100 / 10 10 s k µs t k R TON MAX TON MAX / 10 _ _ (1) (2) (3) (4) (6) (5) (1) Period allotted for G1 and G2 to avoid concurrent ON state at continuous mode operation. VDS2 I1 I2 VG1 VG2 tMAX_ON tMAX_ON VCC x 1.4 VOUT Primary Side Controller + - -100mV S Q R VCCx1.4 Compulsion ON TIME -6mV MAX_TON BLOCK MAX_TON GND LDO BLOCK + - SR_GND DRAIN_COMP SET_COMP RESET_COMP Compulsion OFF TIME VG1 I1 I2 VDS2 VG2 Np Ns VH RMAX_TON R1 C1 Vf D1 RDRAIN1 RDRAIN2 LFB Figure 2. The drive sequence in continuous mode operation |
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