Texas Instruments manual 3 UCC2891EVM Electrical Performance Specifications, Schematic

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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 A ≤ IOUT ≤ 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 ≤ VIN≤ 72 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 A ≤ IOUT ≤ 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 the 48-V input voltage source connector and J8 is the output and return for the 3.3-V output 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 is low-side referenced, Q1 must be a P-channel type 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 –November 2003 –Revised December 2006 Using the UCC2891 Active Clamp Current Mode PWM Controller 5

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