Datasheet

EVM Test Setup

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5.1 Output Load (LOAD1)

For the output load to VOUT, a programmable electronic load set to constant-current mode and capable of

sinking between 0A

and 30A

, is used. Using a dc voltmeter, V2, making all output voltage

measurements directly at J9 and J10 pins is advised. Unless the load has remote-sense capability,

measuring VOUT at LOAD1 results in some voltage measurement error, especially at higher load current,

due to finite voltage drops across the wires between J8 and the electronic load.

5.2 DC Input Source (VIN)

The input voltage is a variable DC source capable of supplying between 0 V

and 72 V

at no less than

3.5 A

, and connected to J1 and A1 as shown in Figure 2. For fault protection to the EVM, limiting the

source current to no more than 4 A

for a 36 V input is a good common practice. A dc ammeter, A1 is

also inserted between VIN and J1 as shown in Figure 2.

5.3 Network Analyzer

A network analyzer connects directly to J6 and J7. The UCC2891EVM-520 provides a 51.1-Ω resistor

(R25) between the output and the voltage feedback to allow easy non-invasive measurement of the

control-to-output loop response.

5.4 Output Ripple Measurement

An oscilloscope probe is connected using scope jack J13 to measure output ripple as shown in Figure 2.

Set the scope to be AC coupled, 50 mV/div. amplitude resolution, 2-µs/div. time resolution and 20-MHz

bandwidth limited.

5.5 Recommended Wire Gauge

The connection between the source voltage, VIN and J1 of the EVM carry as much as 3.25A

. The

minimum recommended wire size is AWG #20 with the total length of wire less than 8 feet (4-feet input, 4-

feet return). The connection between J8 of the EVM and LOAD1 carries as much as 30A

. The minimum

recommended wire size is AWG #16, with the total length of wire less than 8 feet (4-feet output, 4-feet

return).

5.6 Fan

Most power converters include components that are hot to the touch when approaching temperatures of

605°C. Because this EVM is not enclosed to allow probing of circuit nodes, a small fan capable of 200-400

LFM is recommended to reduce component temperatures when operating at or above 50% maximum

rated load current.

48-V to 3.3-V Forward Converter With Active-Clamp Reset Using the SLUU407A–June 2010–Revised May 2013

UCC2891 Active-Clamp Current-Mode PWM Controller

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