Datasheet

1.5

UCCx813 0 / 1/ 2 / 4 : F

R C

UCCx813 3, UCCx813 5 : F

R C

- - - - =

- - =

UCC2813-0, UCC2813-1, UCC2813-2, UCC2813-3, UCC2813-4, UCC2813-5

UCC3813-0, UCC3813-1, UCC3813-2, UCC3813-3, UCC3813-4, UCC3813-5

SLUS161D –APRIL 1999–REVISED JUNE 2013

www.ti.com

RC: RC is the oscillator timing pin. For fixed frequency operation, set the timing-capacitor charging current by

connecting a resistor from REF to RC. Set frequency by connecting a timing capacitor from RC to GND. For best

performance, keep the timing capacitor lead to GND as short and direct as possible. If possible, use separate

ground traces for the timing capacitor and all other functions.

The frequency of oscillation is estimated with the following equations:

where

• frequency is in hertz

• resistance is in ohms

• capacitance is in farads (1)

The recommended range of timing resistors is between 10 and 200 k and timing capacitor is 100 to 1000 pF.

Never use a timing resistor less than 10 k.

REF: REF is the voltage reference for the error amplifier and also for many other functions on the IC. REF is also

used as the logic power supply for high speed switching logic on the IC.

When VCC is greater than 1 V and less than the UVLO threshold, REF is pulled to ground through a 5-kQ

resistor which means that REF is used as a logic output indicating power-system status. For referencing stability,

bypassing REF to GND with a ceramic capacitor as close to the pin as possible is important. An electrolytic

capacitor is also used in addition to the ceramic capacitor. A minimum of 0.1-µF ceramic is required. Additional

REF bypassing is required for external loads greater than 2.5 mA on the reference.

To prevent noise problems with high speed switching transients, bypass REF to ground with a ceramic capacitor

very close to the IC package.

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 will be higher, depending on

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 2.

OUT

= Q

× F (2)

To prevent noise problems, bypass VCC to GND with a 0.1-µF ceramic capacitor in parallel as close to the VCC

pin as possible. An electrolytic capacitor can also be used in addition to the ceramic capacitor.

Product Folder Links: UCC2813-0 UCC2813-1 UCC2813-2 UCC2813-3 UCC2813-4 UCC2813-5 UCC3813-0

UCC3813-1 UCC3813-2 UCC3813-3 UCC3813-4 UCC3813-5