Switching Regulator

Output voltage
This is the maximum voltage that can be applied to the output pins. Voltage cannot be applied externally to the output pin of a 3-terminal regulator, but a voltage from 0 V to the rated value can be applied to the output pin (s) of a control IC.

Output current
This is the current that flows into the on-chip output transistors.

Miss-operation prevention circuit for low level supply voltage
This circuit stops operation of the IC until the operation start voltage is reached after the power supply voltage rises. It also stops operation when the power supply voltage drops to a certain level.

Standby current
This is the current that flows in the IC when operation has been stopped by the miss-operation prevention circuit for low level supply voltage. The smaller the standby current, the better.

Circuit (operating) current
This is the current that flows in the IC while the IC is operating. The smaller the circuit current, the better.

Threshold voltage
The threshold voltage values are the upper and lower limits of the triangular waveform generated by the IC internally. The output duty at the threshold voltage is either 0% or 100% (or maximum value in the case of the uPC494) .

Master-slave operation
This means the synchronous operation of multiple switching regulators via the on-chip oscillator of another switching regulator IC.

At the beginning of the uPC1909 Data Sheet, there is a sentence that goes, "It is necessary to obtain license from Vicor Corporation before using the uPC1909 in an active-clamp type circuit."
What is the patent number?

The patent number of active clamp is "USP No.4,441,146".
It seems that Vicor call it Reset Patent.
For details, see the home page of Vicor.

Note that negotiations concerning use of the patent should be directly made between Vicor and the customer, and that NEC has nothing to do with such negotiations.

How is the output circuit of a switching regulator configured?

There are three types of configurations.

• Totem pole
• Open collector/open drain
• Push-pull

(1) Totem pole
A power MOS FET is generally used as the main switching element of a switching power supply. In order to drive a power MOS FET at high speeds, the gate capacitor of the power MOS FET must be charged and discharged very quickly.
A totem pole circuit is a pre-driver circuit that can supply a large peak current to enable the power MOS FET's gate capacitor to be charged and discharged as quickly as possible.
A simple switching power supply circuit can be configured by incorporating a totem pole circuit in the control IC.

Totem Pole Driver



(2) Open collector/open drain
Using this type of configuration makes it possible to design a driver that ideally matches the characteristics of the main switching element.

Open Collector and External Driver



(3) Push-pull
"Push-pull" is the name of a switching power supply circuit system. With this system, two main switching elements are used and the switching transformers are driven alternately. This system raises the utilization ratio of the transformers, making it ideal for switching power supplies with large outputs.

In push-pull switching power supplies, dead time is built in to prevent two transistors turning on at the same time. Setting this dead time is easy in the uPC494.

Can a negative voltage be output when a positive voltage is input?

Yes, it can.
The output that can be obtained differs depending on the circuit configuration, as follows.

• Output voltage lower than input voltage (step down)
• Output voltage higher than input voltage (step up)
• Output voltage that has reverse polarity to input voltage (inverted)

How can I calculate the total power dissipation of the uPC494?

The power consumption or dissipation of the uPC494 when operating can be calculated by monitoring the VCC pin voltage and the current that flows into the device.
Since the output stage is an open collector, the dissipation at the output stage can also be calculated by monitoring the output voltage and output current waveforms in a similar manner. The total power dissipation can therefore be determined by adding these two dissipation values together.

(2006/09)

Can the uPC494 shut off the output if the dead time control input pin (pin 4) is made high?

Yes, it can.
If a voltage of 3.3 V or more (less than VREF) is applied to this pin, the transistor at the output stage is turned off.

An offset voltage of about 0.1 V is given to the dead time comparator of the uPC494.
If the capacitance of the timing capacitor increases, however, there is a possibility that the dead time duty decreases to 0%.
For this reason, care must be exercised when using the uPC494 in the push-pull mode.

For details, refer to "4.5 Oscillation Frequency - Threshold Voltage of PWM Comparator (dead time control)" in the Application Note.

What is the difference between the "standby current" and "off current" of the uPC1099.

Standby current:	The output is shut down if the supply voltage drops below 8 V. The supply current in this state is called the standby current.
Off current:	The supply current when the uPC1099 is turned off by using the ON/OFF pin while it operates normally is called the off current.

It seems that the uPC1100 operates when its timer latch voltage exceeds 2.25 V.
Because the voltage of the triangular wave is 1.45 to 2.05 V, however, it is suspected that the output is in the ON state (DC) and the driver elements such as MOS are damaged at 2.25 V.

What should be done to produce an output at a specific duty factor even if the output is short-circuited?

As pointed out, settings must be performed so that the output is not in the DC state.
For this setting, the dead time control pins are used.

The DC state can be avoided if the voltage on the dead time control pins is set to a value lower than the peak of the triangular wave (2.05 V).

Adjust the voltage of the dead time control pins (pins 6 and 11) so that the output is not in the ON state, by referring to Figure 3 Operation Waveform in "5. Block Diagram and Operation Waveform" of the User's Manual (Japanese).

The output of the uPC1100 overshoots when the power is provided.

Generally, it is recommended to use the soft start function (by connecting a capacitor to pin 6).

How can one check if the uPC1935 oscillates?

Unfortunately, there is no way to check whether or not it oscillates.
If no output waveform is produced, the chances are that the output is shut down because the timer latch circuit operates due to noise, etc.
Therefore, short-circuit the DLY pin to GND to disable the timer latch circuit and check the operation.

Exercise care in short-circuiting the output when conducting an experiment because the output short-circuit protection feature is not activated in this status.

I designed my circuit according to the description in the manual, but it still won't operate.

Check the following.

• Is there any incorrect wiring?
• The GND wiring can sometimes be a cause of malfunction. Make sure that the GND pins for signal lines and power lines are separate, and that each is grounded to a separate point.
• Is there a capacitor connected between the V_REF (REFERENCE, REF) and GND pins? If so, be sure to use a film, tantalum, or ceramic capacitor.

A pulse is sometimes output continuously during push-pull operation.

Noise may have entered the GND pin causing malfunction. Check your ground wiring.
Is there a capacitor connected between the Ref Out pin (pin 14) and GND pin (pin 7)? If so, be sure to use a film, tantalum, or ceramic capacitor.

My device sometimes operates and sometimes doesn't.

The timer latch circuit may be malfunctioning. Check the following.

• Is there any incorrect wiring?
• The GND wiring can sometimes be a cause of malfunction. Make sure that the GND pins for signal lines and power lines are separate, and that each is grounded to a separate point.
• Is there a capacitor connected between the REF OUT pin (pin 16) and GND pin (pin 8)? If so, be sure to use a film, tantalum, or ceramic capacitor.
• Be sure to ground the GND side of the delay capacitor C_DLY connected to the DLY pin (pin 15) as close as possible to the GND pin (pin 8).
• When using the ON/OFF control pin (pin 4), ensure that the signal input to this pin rises at no more than 0.07V/us.

If I short-circuit one output in the uPC1100, only that output is cut off (both outputs are not cut off).

The timer latch circuit may be malfunctioning. Check the items listed in A1 above.