Texas Instruments UCC2891 User Manual
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UCC2891EVM Electrical Performance Specifications

3UCC2891EVM Electrical Performance Specifications

The UCC2891EVM electrical performance specifications are listed in Table 1.

Table 1. UCC2891EVM Performance Summary

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

Input Characteristics

 

 

 

 

 

Input voltage range

 

36

48

72

V

No load intput current

VIN = 36 V, IOUT = 0 A

 

75

100

mA

Maximum input current

VIN = 36 V, IOUT = 30 A

 

3.00

3.25

A

Input voltage ripple

VIN = 72 V, IOUT = 30 A

 

1.50

1.75

VP-P

Input voltage ripple

 

 

 

 

 

Output voltage

36 V VIN 72 V, 0 AIOUT 30 A

3.25

3.30

3.35

V

Output voltage regulation

Line regulation (36 V VIN 72 V, IOUT = 0 A)

 

0.003%

 

 

 

Load regulation (0 A IOUT 30 A, VIN = 48 V)

 

0.060%

 

 

Output voltage ripple

VIN = 48 V, IOUT = 30 A

 

30

35

mVP-P

Output load current

VIN = 48 V, IOUT = 30 A

0

 

30

A

Output current limit

36 V VIN72 V

 

 

32

 

 

 

Output current limit

 

 

 

 

 

Switching frequency

 

275

 

325

kHz

Control loop bandwidth

36 V VIN 72 V, IOUT = 10 A

5

 

8

 

 

Control loop bandwidth

36 V VIN 72 V, 2 AIOUT 30 A

30

 

50

°C

Peak efficiency

 

 

92%

 

 

Full load efficiency

VIN = 48 V, IOUT = 30 A

 

89%

 

 

4Schematic

A schematic of the UCC2891EVM is shown in Figure 1. Terminal block J1 is the48-Vinput voltage source connector and J8 is the output and return for the3.3-Voutput voltage.

On the primary side, U1 is the UCC2891 shown with the necessary discrete circuitry for configuring the controller to operate at 300 kHz with the maximum duty clamp set for 0.65. The EVM is programmed to start at VIN=36 V, as determined by R11 and R12. To minimize power dissipation in the current sense, a current sense transformer, T1 is used, as opposed to simply using a sense resistor between the source of Q2 and power ground. Q2 is the primary switching MOSFET and is selected based upon VDS and low RDS(on). Q1 is the AUX (active reset) MOSFET and is selected based upon preferred package only, with

only minor consideration given for RDS(on) and Qg. Since the active clamp used in this design islow-sidereferenced, Q1 must be aP-channeltype MOSFET. The reason for this is further explained in application note SLUA299[2]. C9 is the clamp capacitor used to maintain a constant dc voltage. The input voltage is subtracted from the clamp voltage to allow transformer reset during the active clamp period.

SLUU178A –November2003–RevisedDecember 2006

Using the UCC2891 Active Clamp Current Mode PWM Controller

5

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Schematic

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Figure 1. UCC2891EVM Schematic

6

Using the UCC2891 Active Clamp Current Mode PWM Controller

SLUU178A –November2003–RevisedDecember 2006

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