UCC2541

SLUS621A − AUGUST 2004 − SEPTEMBER 2005

9

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APPLICATION INFORMATION

The UCC2541 is a high-efficiency synchronous buck controller that can be used in many point-of-load

applications.

CEA− and VEA− pins: Current Limit and Hiccup Mode

Typical power supply load voltage versus load current is shown in Figure 2. This figure shows steady state

operation for no-load to overcurrent shutdown (soft-start retry is not depicted in the diagram). During the voltage

regulation conditions, the voltage error amplifier output is lower than the current error amplifier, allowing the

voltage error amplifier to control operation. During the current limit conditions, the current error amplifier output

is lower than the voltage error amplifier, allowing the current error amplifier to control operation. The boundary

between voltage and current control occurs when the difference between CEA− and VEA− tries to exceed

50 mV.

Current limiting begins to occur when the difference between CEA− and VEA− exceeds 50 mV. For currents

that exceed this operating condition, the UCC2541 controls the converter to operate as a pure current source

until the output voltage falls to half of its rated steady state level. Then the UCC2541 sets both G1 and G2 outputs

to LOW and it latches a fault that discharges the soft-start voltage at 30% of its charging rate. The UCC2541

inhibits a retry until the soft-start voltage falls below 0.5 V. A functional diagram of the voltage and current error

amplifiers is shown in Figure 3.

UDG−04053

Shutdown

Limited

Current

ILOAD − Load Current − A

VREG

Figure 2. Typical Power Supply Load Voltage vs Current