Features

100A typical startup supply current, 500A typical operating supply current, run to 1MHz, internal soft-start, internal fault soft-start, internal leading edge blanking for current sense signal, 1 amp totem pole output, current sense to gate drive output typical 70ns response
, 1.5% tolerance voltage reference, same pinout as UCC3802 , UC3842 and UC3842A All control and drive components required for frequency current mode switching power supplies with minimal part count.
These devices have the same pinout configuration as the UC3842/3/4/5 family, but also offer the additional features of internal full-cycle soft-start and internal leading edge blanking of the current sense inputs.
The UCC1313-0/- 1/- 2/- 3/- 4/- 5 series offers a variety of package options, temperature range selection, maximum duty cycle selection, and threshold voltage level selection. Lower reference parts such as the UCC3813-3 and UCC3813-5 are best for battery powered systems, while the higher reference and higher UV hysteresis of the UCC3813-2 and UCC3813-4 make these parts ideal for off-line power supplies .
The UCC2813-x series is suitable for operation from -40°C to +85°C, while the UCC3813-x series is suitable for operation from 0°C to +70°C.

block diagram

COMP: COMP is the output of the error amplifier and the input of the PWM comparator.
Unlike other devices, the error amplifier in the UCC3813 family is a true, low output impedance, 2 MHz op amp. Therefore, the COMP terminal can source and sink current at the same time. However, the error amplifier has limited internal current, so you can command zero duty cycle by externally forcing COMP to ground.
The UCC3813 series has a built-in full-cycle soft-start function. Soft-start is implemented as a clamping of the maximum COMP voltage.
FB: FB is the inverting input of the error amplifier. For best stability, keep the FB lead length as short as possible and keep the FB stray capacitance as small as possible.
CS: CS is the input to the current sense comparator. The UCC3813 family has two different current sense comparators: PWM comparators and overcurrent comparators.
The UCC3813 family includes digital current-sense filtering that disconnects the CS terminal from the current-detection comparator within a 100ns interval immediately following the rising edge of the output pin. This digital filtering, also known as leading edge blanking, means that in most applications, no analog filtering (RC filter) is required for CS. The leading edge blanking technique provides a smaller effective CS-to-OUT propagation delay compared to external RC filter techniques. However, note that the minimum non-zero turn-on time of the output signal is directly affected by the leading edge blanking and CS to OUT propagation delay.
The overcurrent comparator is used for fault detection only, exceeding the overcurrent threshold will cause a soft-start cycle.
RC: RC is the oscillator timing pin. For fixed frequency operation, set the timing capacitor charge current by connecting a resistor from REF to RC. The frequency is set by connecting a timing capacitor from RC to GND. For best performance, keep the timing capacitor leads as short and direct as possible to ground. If possible, use separate ground traces for timing capacitors and all other functions.

The oscillation frequency can be estimated by the following equation:
UCCx813-0/-1/-2/-4:F Standard RC 15.
UCCx813-3, UCCx813-5:F
RC
10.
where frequency is in Hertz, resistance is in inches, and capacitance is in farads. The recommended range for the timing resistor is 10k to 200k and the timing capacitor is 100pF to 1000pF. Never use a timing resistor smaller than 10k.
GND: GND is the reference ground and power ground for all functions in this part.
Output: The output is the output of a high current power driver capable of driving the gate of a power MOSFET with peak currents in excess of 750mA. OUT is low when VCC is below the UVLO threshold.
The high-current power driver consists of FET output devices, which can be switched all the way to GND and all the way to VCC. The output stage also provides a very low impedance overshoot and overshoot. This means that in many cases, external Schottky clamp diodes are not required.
VCC: VCC is the power input connection for this device. In normal operation, VCC is powered through a current limiting resistor. Although the quiescent VCC current is very low, the total supply current will be higher, depending on the output current. The total VCC current is the sum of the quiescent VCC current and the average output current. Knowing the operating frequency and the MOSFET gate charge (Qg), the average output current can be calculated from:
I see. To prevent noise issues, bypass VCC to GND using a 0.1F ceramic capacitor as close to the VCC pin as possible. In addition to ceramic capacitors, electrolytic capacitors can also be used.
REF:REF is the voltage reference for the error amplifier and for many other functions on the integrated circuit. REF is also used as a logic power supply for high-speed switching logic on the IC.
When VCC is greater than 1V and less than the UVLO threshold, REF is pulled to ground through a 5k resistor. This means that REF can be used as a logic output indicating the state of the power system. An important point for reference stability is to bypass REF to GND with a ceramic capacitor as close to the pin as possible. In addition to ceramic capacitors, electrolytic capacitors can also be used. At least 0.1F ceramic is required. For external loads greater than 2.5mA on the reference, additional reference bypassing is required.
To prevent noise problems with high-speed switching transients, bypass REF to ground with a ceramic capacitor very close to the IC package.

application information

UCC3813-0/-1/-2/-3/-4/-5 oscillators generate sawtooth waves on RC. The rise time is set by the time constants of RT and CT. The fall time is set by CT and the internal transistor on-resistance is about 125. At the fall time, the output is turned off and the maximum duty cycle is reduced to below 50% or 100% depending on the number of parts. Larger timing capacitors increase discharge time and reduce maximum duty cycle and frequency.