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ICE2A0565 데이터시트(PDF) 14 Page - Infineon Technologies AG |
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ICE2A0565 데이터시트(HTML) 14 Page - Infineon Technologies AG |
14 / 36 page Version 2.6 14 25 Dec 2006 CoolSET™-F2 Functional Description the Current-Limit Comparator cannot switch off the gate drive. 3.5.2 Propagation Delay Compensation In case of overcurrent detection by ILimit the shut down of CoolMOS™ is delayed due to the propagation delay of the circuit. This delay causes an overshoot of the peak current Ipeak which depends on the ratio of dI/dt of the peak current (see Figure 17). . Figure 17 Current Limiting The overshoot of Signal2 is bigger than of Signal1 due to the steeper rising waveform. A propagation delay compensation is integrated to bound the overshoot dependent on dI/dt of the rising primary current. That means the propagation delay time between exceeding the current sense threshold Vcsth and the switch off of CoolMOS™ is compensated over temperature within a range of at least. Figure 18 Dynamic Voltage Threshold Vcsth The propagation delay compensation is done by means of a dynamic threshold voltage Vcsth (see Figure 18). In case of a steeper slope the switch off of the driver is earlier to compensate the delay. E.g. Ipeak = 0.5A with RSense = 2. Without propagation delay compensation the current sense threshold is set to a static voltage level Vcsth=1V. A current ramp of dI/dt = 0.4A/µs, that means dVSense/dt = 0.8V/µs, and a propagation delay time of i.e. tPropagation Delay =180ns leads then to a Ipeak overshoot of 14.4%. By means of propagation delay compensation the overshoot is only about 2% (see Figure 19). Figure 19 Overcurrent Shutdown 3.6 PWM-Latch The oscillator clock output applies a set pulse to the PWM-Latch when initiating CoolMOS™ conduction. After setting the PWM-Latch can be reset by the PWM- OP, the Soft-Start-Comparator, the Current-Limit- Comparator, Comparator C3 or the Error-Latch of the Protection Unit. In case of resetting the driver is shut down immediately. 3.7 Driver The driver-stage drives the gate of the CoolMOS™ and is optimized to minimize EMI and to provide high circuit efficiency. This is done by reducing the switch on slope when reaching the CoolMOS™ threshold. This is achieved by a slope control of the rising edge at the driver’s output (see Figure 20) to the CoolMOS™ gate. Thus the leading switch on spike is minimized. When CoolMOS™ is switched off, the falling shape of the driver is slowed down when reaching 2V to prevent an overshoot below ground. Furthermore the driver circuit is designed to eliminate cross conduction of the output stage. At voltages below the undervoltage lockout threshold VVCCoff the gate drive is active low. t I Sense I Limit t Propagation Delay I Overshoot1 I peak1 Signal2 Signal1 I Overshoot2 I peak2 0 RSense dIpeak dt ------------ × dVSense dt --------------- ≤≤ t V csth V OSC Signal1 Signal2 V Sense max. Duty Cycle off time t Propagation Delay 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 with compensation without compensation dt dV Sense V V/us |
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