ICE3BRxx65JF is the latest integrated power IC; F3R CoolSET in Fullpak package. The PWM controller is inherited from the F3R DIP-8 CoolSET. Combined with the state-of-art MOSFET; CoolMOS and housed in the TO-220 6-lead Fullpak package, it can work in medium power range from 40W to 150W with reduced PCB area. It is suitable for medium power applications such as DVD player/recorder, blue ray player/recorder, set-top box, adapter, auxiliary supply, LCD monitor, LCD TVD, etc.
The two most distinguished features are active burst mode and frequency jittering which can provide very high energy efficiency at standby mode and low EMI radiation. Other basic features include wide Vcc range, soft start, adjustable blanking time for over load, propagation delay compensation, built-in auto-restart protection features such as Vcc OVP, OLP, open loop, OTP, external protection enable pin, etc.
The ICE3BRxx65JF can meet Efficiency Level Mark IV easily. With all those technologies and features in a Fullpak package, ICE3BRxx65JF is an ideal solution for medium power application.
LIST OF IMPORTANT FEATURES• 650V avalanche rugged CoolMOS with built-in Startup Cell
• 67kHz fixed switching frequency with frequency jittering feature
• BiCMOS technology provide wide VCC range
• Active Burst Mode leads best-in class low standby power
• Soft gate driving with frequency jitter feature for low EMI performance
• Auto restart protection mode for over-load, open loop, Vcc over-voltage, Vcc under-voltage & over-temperature
• Built-in and extendable blanking window for short duration of maximum system power
• External auto-restart enable protection pin
APPLICATION CIRCUITSince ICE3BRxx65JF is a PWM controller integrated with MOSFET and with all necessary features and functions, the circuitry connected to the device is much simplified and it can save a lot of PCB area. A full featured power supply control is done by just adding a few capacitors and resistors (refer to Figure 1).
Figure 1: 100W, 18V/5.56A basic application circuit using ICE3BR0665JF.KEY FUNCTIONS DESCRIPTIONActive Burst ModeTo obtain a very low standby power, it needs to minimize at both conduction and switching losses at light load. ICE3BRxx65JF is a BiCMOS design with start-up cell which can effectively reduce the power consumption due to IC controller and the external power up resistors. However, the major losses come from the switching loss of the switching elements. The active burst mode is employed to reduce the effective switching frequency in response to the output loading by means of skipping switching cycles. The burst mode scheme is very robust and it would not make the system unstable but it can achieve an extreme low standby power.
The control scheme of the active burst mode is as below.
During light load operation, the feedback voltage drops with the load. When the VFB voltage falls below 1.22V for 20ms, the ICE3BRxx65JF enters the Active Burst Mode. After entering the burst mode, the feedback control level is shifted to operate between 3.1V and 3.6V. The system will stop switching when the feedback voltage hits 3.1V which means the output voltage is still within regulation. When the feedback voltage increases and hits 3.6V, the system starts switching which means the output voltage is dropped to the lower limit of regulation. During the burst on period, the current sense limit is reduced to 1/4 of the normal control, which can effectively reduce the audible noise. When the output loading increases to nominal load, the feedback voltage will rise with the output voltage drops. When it hits 4.5V, the system is released from active burst mode and recovers to normal operation (refer to Figure 2). Since the ICE3BRxx65JF is continuously monitoring the feedback voltage, the response on the load jump is fast and with minimum output drops.
Figure 2: Operating diagram for the active burst mode.The measured standby power at no load is 92mW, at 0.3W load is 0.51W and at 0.5W load is 0.76W for 265Vac input voltage (refer to figure 3).
Figure 3: Standby power of power supply employing ICE3BR0665JF (no load, 0.3W and 0.5W load).Switching frequency Modulation (frequency jittering) The purpose of implementing the switching frequency modulation is to obtain good EMI performance by means of evening out the peak energy in one particular frequency to a spread of frequency. The selected frequency spread width is +/-4% of the switching frequency; 67kHz ± 2.7kHz and the switching modulation period is 4ms (250Hz). The frequency modulation is achieved by an internal saw tooth signal which being generated by digital method, controls the jittering pattern of the switching clock such that the switching frequency reaches maximum at trough and decrease linearly to the minimum at the crest of the saw tooth waveform (refer to figure 4).
Figure 4: Switching frequency modulation and measured waveform.An EMI plot of 100W system employed with ICE3BR0665JF is showed in Figure 5. It shows there is at least 5~10dB level from the average limit line.
Figure 5: Conducted EMI plots with ICE3BR0665JF at 100W load 230VacPropagation Delay CompensationCurrent mode PWM control employs peak current control. However, the peak current control is inaccurate with the changes of input voltage. When the peak current is hit, there is a propagation delay time due to internal logic circuit before the switching pulse stops. This propagation delay time is fixed in the IC controller but the peak current is varied with current rise time; ΔI/Δt, which can be varied by 3 times between low input line and high input line. The peak current control becomes inaccurate along a wide input voltage range. And thus the maximum power control is also inaccurate.
The controlled peak current will have overshoot from the pre-set peak current limit. The degree of overshoot will depend on the rise time of the current; a faster current rate will have a larger overshoot and a slower one will have less overshoot. A very important relationship is found that the faster current rate has smaller duty ratio and slower one has larger duty ratio. It is employed as the basis of the propagation delay compensation. The compensation scheme is to vary the peak current limit with different duty ratio such that a faster current rate condition has a lower peak current limit and a slower one has a higher current limit (refer to Figure 6). With this compensation, the maximum power is almost independent on the input voltage.
Figure 6: Propagation delay compensation.The ICE3BRxx65JF implemented with propagation delay compensation circuit can effectively reduce the peak current inaccuracy. A demo board with ICE3BR0665JF is measured and the maximum peak output power is around 4% along a wide input voltage (refer to Figure 7).
Figure 7: Measured maximum power of the power supply using ICE3B0665JF.Average EfficiencyThe measured average efficiency of 25%, 50%, 75% and 100% load is 85.5% and 86.3% for 115Vac and 230Vac respectively. Together with the 92mW standby power at no load, it is very easy to meet the Efficiency Level Mark IV where the requirement is large than 85% average efficiency at 115Vac and 230Vac and the standby power for no load condition is less than 0.5W.
Figure 8: Average efficiency curve.Protection FeaturesProtection is one of the major factor to determine whether the system is safe and robust. Therefore sufficient protection is necessary. ICE3BRxx65JF provide all the necessary protections to ensure the system is operating safely. The protections include Vcc over-voltage, over-temperature, over-load, open loop, Vcc under-voltage, short opto-coupler, external protection enable, etc. When those faults are found, the system will go into auto-restart which means the system will stop for a short period of time and re-start. If the fault persists, the system will stop again. It is then until the fault is removed, the system resumes to normal operation. A list of protections and the failure conditions is showed in Table 1.
Table 1: List of protections
Blanking time (basic and extendable) for over-load protectionOver-load protection is very important for a power supply as it would protect the power supply from over-heating after pro-long over-load. However, if the timing to protect is too fast, it would become not flexible enough for the application. ICE3BRxx65JF provides a blanking time scheme which goes to protection after a desired blanking time elapsed such that it can provide sufficient protection and at the same time maintains certain degree of flexibility.
The blanking time scheme is divided into 2 modes; basic mode and extended mode. In basic mode scheme, the blanking time is set at 20ms; i.e. system will go to protection after 20ms blanking time. In the extended mode scheme, the blanking time can be increased by adding an external capacitor (CBK) at BA pin in addition to the basic mode; i.e. overall blanking time = basic + extended.
When there is an over-load fault, the feedback (FB) voltage will go up and hits 4.5V. Then the blanking time scheme activated. The scheme will first go to basic mode; 20ms. If there is no CBK capacitor at BA pin, the voltage at BA pin will charge up immediately from 0.9V to 4.0V by an internal current source; 13uA. Then it will trigger the auto-restart protection immediately. If there is a CBK capacitor at BA pin, the protection can only be triggered when the BA pin hits 4.0V with the additional charging time from 0.9V to 4.0V by 13uA. This period of charging is called the extended blanking time (refer to figure 9).
Figure 9: ICE3B0665JF Blocking diagram for blanking time during over-load protection.Total blanking time,
Figure 10 shows the captured waveform for basic mode (left) and extended mode (right) blanking time for over-load protection.
Figure 10: Blanking time for over-load protection; basic mode (left) and extended mode (right).CONCLUSIONICE3BRxx65JF series F3R CoolSET is the latest integrated power IC. It consists of best-in class CoolMOS, best-in class low standby power, good EMI performance, tight maximum power control, sufficient and flexible protection, easy to meet Efficiency Level Mark IV, etc. All those technologies and features make ICE3BRxx65JF the most suitable for the various medium power applications.
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