Features Fixed 60kHz switching frequency 9V to 38V Wide range VDD voltage Current mode control Auxiliary undervoltage lockout with hysteresis W-8, 13 W for DIP-8 – Europe (85-265 VAC) 5 W for SO-8, 8 W for DIP-8
Description The Viper12A combines a dedicated current-mode PWM controller and a high-voltage power MOSFET on the same silicon die.
Typical applications include offline power for battery charger adapters, backup power for TVs or monitors, auxiliary power for motor control, and more. The internal control circuitry provides the following advantages: large input voltage range on the VDD pin to accommodate changes in auxiliary supply voltage (this feature is ideal for battery charger adapter configurations), automatic burst mode at low load conditions and overdrive in HICCAP mode. voltage protection.

Rectangular UI Output Feature Rectangular UI Output Feature for Battery Charger

A complete regulation scheme enables combined and precise output characteristics. Secondary feedback is provided through an optocoupler driven by the TSM101 . The device provides two op amps and a voltage reference, allowing the output voltage and current to be regulated. The combination of integrated or functional execution of the two resulting error signals results in dual voltage and current limiting, known as the rectangular output characteristic. This type of power supply is especially suitable for battery chargers, whose output is mainly used in current mode in order to provide a specified charge rate. Precise voltage regulation is also handy for lithium-ion batteries that require both modes of operation.

Wide voltage range for vdd
"The voltage range of the vdd pin extends from 9 V to V 38. This feature provides great flexibility in implementing various behaviors in the design. In understanding the long-term configuration of C 4 7 pages have been chosen to supply the device with two benefits: At the start of fast device switching, it immediately receives some energy from auxiliary winding. C5 can lower therefore and small ceramic chip (100 NF) sufficient to insure the filtering function. In total, start time from voltage on switch input to output The voltage presence also decreased dramatically. The synchronous output current characteristic can be maintained even with very low or zero output voltages. Since "tsm101 is also supplied in forward mode, it enables "current regulation of what the output voltage is." The voltage at the vdd pin Possible or XB6 input voltage, that is to say a wide range of applications with a ratio of about 4 parts.

How the Feedback Pin Works The feedback pin controls the operation of the device. Unlike traditional PWM control circuits that use a voltage input (the inverting input of an op amp), the FB pin is sensitive to current. The internal current mode structure is given.
The internal current control structure power MOSFET provides an induced current proportional to the main current ID. R2 receives this current and the current from the FB pin. Then, the voltage across R2 is compared to a fixed reference voltage of about 0.23 V. The MOSFET is turned off when the following equation is reached:
Current limit is obtained by shorting the FB pin to ground (VFB=0 V). This will result in a negative current supplied by this pin and is expressed as:
The leakage current limit idlim can be obtained by reporting this expression in the previous expression:
In practical applications, the FB pin is driven by an optocoupler, which acts as a pull-up. Therefore, it is impossible to actually short this pin to ground and the above leakage current values are impossible to achieve. However, capacitor C averages the voltage on the FB pin, and when the optocoupler is turned off (started or shorted), the corresponding voltage can be assumed to be very close to 0 V. For low leakage current, as long as IFB meets IFB Internal threshold for VIPER12A. If the IFB exceeds this threshold, the device will stop switching. As shown in Figure 12 on page 14, if the BSD value is specified in the PWM comparator section. In fact, as long as the drain current is about 12% of IDLIM, that is, 50 mA, the device will enter burst mode operation by missing switching cycles. This is especially important when the converter is lightly loaded.
IFB transfer function

Then, the overall DC transfer function can be constructed between ID and IFB, which also takes into account the internal blanking time and its associated minimum turn-on time. This creates a minimal leakage current at which the device can no longer control it in a linear fashion. This leakage current depends on the primary inductance value of the transformer and the input voltage. Two things can happen, depending on the current value versus the fixed 50 mA value, as described above.

Startup Sequence Startup Sequence The device includes a high voltage startup current source connected to the drain of the device. As long as a voltage is applied to the input of the converter, this startup current source is activated as long as VDD is below VDDON. When vddon is reached, the startup current source is turned off and the device starts to work by turning its main power MOSFET on and off. Since the FB pin does not receive any current from the optocoupler, the device operates at full current capacity and the output voltage rises until it reaches the regulation point where the secondary loop starts sending current to the optocoupler. At this point, the converter enters a regulated operation, where the FB pin receives the required amount of current to provide the correct power on the secondary side. This sequence is shown in Figure 7. Note that during the actual start-up phase TSS, the device consumes some energy from the VDD capacitor, waiting for continuous power from the auxiliary winding. If the value of this capacitor is too low, the start-up phase terminates and the converter never starts before any energy is received from the auxiliary winding. This is also illustrated in the same figure in dashed lines.

Over Voltage Threshold An over voltage detector on the Vdd pin allows the viper12a to reset itself when vdd exceeds vddovp. the entire sequence of overvoltage events. Note that this event is only latched for the time it takes for VDD to reach VDDOFF, after which the device automatically resumes normal operation.
Overvoltage Sequence