UCC2802M datasheet(13/55 Pages) TI1

13 / 55 page

Rmax=

VIN:min;-VVCC:max;

IVCC+Qg ×f

OUT

´ f

UCC1800, UCC1801, UCC1802, UCC1803, UCC1804, UCC1805

UCC2800, UCC2801, UCC2802, UCC2803, UCC2804, UCC2805

UCC3800, UCC3801, UCC3802, UCC3803, UCC3804, UCC3805

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SLUS270E – MARCH 1999 – REVISED JUNE 2016

Product Folder Links: UCC1800 UCC1801 UCC1802 UCC1803 UCC1804 UCC1805 UCC2800 UCC2801 UCC2802

UCC2803 UCC2804 UCC2805 UCC3800 UCC3801 UCC3802 UCC3803 UCC3804 UCC3805

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Feature Description (continued)

In these two equations, switching frequency (f) is in Hz, R is in Ω, and C is in farads.

The two equations are different due to different reference voltages. The recommended range of timing resistor

values is between 10 kΩ and 200 kΩ; the recommended range of timing capacitor values is between 100 pF and

1000 pF. The peak-to-peak amplitude of the oscillator waveform is 2.45 V versus 1.7 V in UC3842 family. For

best performance, keep the timing capacitor lead to GND as short as possible. TI recommends separate ground

traces for the timing capacitor and all other pins. The maximum duty cycle for the UCCx802 and UCCx803 is

approximately 99%; the maximum duty cycle for the UCCx803 and UCCx804 is approximately 49%. The duty

cycle cannot be easily modified by adjusting RT and CT, unlike the UC3842A family. The maximum duty cycle

limit is set by the ratio of the external oscillator charging resistor RT and the internal oscillator discharge transistor

on-resistance, like the UC3842. However, maximum duty cycle limits less than 90% (for the UCCx802 and

UCCx803) and less than 45% (for the UCCx804 and UCCx805) can not reliably be set in this manner. For better

control of maximum duty cycle, consider using the UCCx807.

9.3.1.5 GND

GND pin is the signal and power returning ground. TI recommends separating the signal return path and the high

current gate driver path so that the signal is not affected by the switching current.

9.3.1.6 OUT

OUT is the output of a high-current power driver capable of driving the gate of a power MOSFET with peak

currents exceeding 750 mA. OUT is actively held low when VCC is below the UVLO threshold. The high-current

power driver consists of FET output devices, which can switch all of the way to GND and all of the way to VCC.

The output stage also provides a low impedance to overshoot and undershoot. This means that in many cases,

external Schottky clamp diodes are not required.

The output of the UCCx80x is a CMOS output versus a Bipolar output on the UC3842 family. Peak output current

remains the same ±1 A. The CMOS output provides very smooth rising and falling waveforms, with virtually no

overshoot or undershoot. Additionally, the CMOS output provides a low resistance to the supply in response to

overshoot, and a low resistance to ground in response to undershoot. Because of this, Schottky diodes may not

be necessary on the output. Furthermore, the UCCx802 has a self-biasing, active low output during UVLO. This

feature eliminates the gate to source bleeder resistor associated with the MOSFET gate drive. Finally, no

MOSFET gate voltage clamp is necessary with the UCCx80x as the on-chip Zener diode automatically clamps

the output to VCC.

9.3.1.7 VCC

VCC is the power input connection for this device. In normal operation, VCC is powered through a current

limiting resistor. Although quiescent VCC current is very low, total supply current is higher, depending on the

OUT current. Total VCC current is the sum of quiescent VCC current and the average OUT current. Knowing the

operating frequency and the MOSFET gate charge (Qg), average OUT current can be calculated from

Equation 6.

(6)

The UCCx80x has a lower VCC (supply voltage) clamp of 13.5 V typical versus 30 V on the UC3842. For

applications that require a higher VCC voltage, a resistor must be placed in series with VCC to increase the

source impedance. The maximum value of this resistor is calculated with Equation 7.

(7)

In Equation 7, VIN(min) is the minimum voltage that is used to supply VCC, VVCC(max) is the maximum VCC

clamp voltage and IVCC is the IC supply current without considering the gate driver current and Qg is the external

power MOSFET gate charge and f is the switching frequency.

Additionally, the UCCx80x has an on-chip Zener diode to regulate VCC to 13.5 V. The turnon and turnoff

thresholds for the UCCx80x family are significantly different: 12.5 V and 8 V for the UCCx802 and UCCx804;

4.1 V and 3.6 V for the UCCx803 and UCCx805. 5-V PWM operation is now possible. To ensure against noise

related problems, filter VCC with an electrolytic and bypass with a ceramic capacitor to ground. Keep the

capacitors close to the IC pins.

UCC2802M Datasheet(PDF) 13 Page - Texas Instruments

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