ANALOG DEVICES DC2995A High Frequency, Step Down Supply, GaN FETs User Manual

: October 27, 2023
: Analog Devices

Table of Contents

DESCRIPTION
PERFORMANCE SUMMARY
PARTS LIST
SCHEMATIC DIAGRAM
Documents / Resources

ANALOG - logo1 DEMO MANUAL DC2995A

DESCRIPTION

Demonstration circuit 2995A is a buck regulator featuring the LTC®7891. The DC2995A operates from a 36V to 72V input voltage range and generates a 12V, 20A output.
The LTC7891 has a precision voltage reference which can generate an output voltage with 2% tolerance over the full operating conditions. The 500kHz switching frequency operation results in a small and efficient circuit. The con- verter achieves over 96% efficiency with 20A load.

LTC7891 High Frequency Step-Down Supply with GaN FETs

The demonstration circuit can be easily modified to regulate output voltages from 0.8V to 60V.
The DC2995A provides a high performance cost-effective solution for generating a 12V output. The LTC7891 data sheet gives a complete description of this part, its operation and application information and must be read in conjunction with this demo manual.
Design files for this circuit board are available.
All registered trademarks and trademarks are the property of their respective owners.

PERFORMANCE SUMMARY

Specifications are at TA = 25°C

PARAMETER	CONDITIONS	MIN	TYP	MAX	UNITS
Minimum Input Voltage	IOUT = 0A to 20A

36

| V
Maximum Input Voltage| IOUT = 0A to 20A|

72

| V
Output Voltage| VIN = 36V to 72V|

12 ±2%

| V
Output Voltage Ripple| VIN = 48V, IOUT = 20A|

300

| mVP-P
Nominal Switching Frequency| |

500

| kHz

QUICK START PROCEDURE

Demonstration circuit 2995A is easy to set up to evaluate the performance of the LTC7891. For proper measurement equipment setup refer to Figure 1 and follow the procedure below.
NOTE: When measuring the input or output voltage ripple, care must be taken to minimize the length of oscilloscope probe ground lead. Measure the input or output oltage ripple by connecting the probe tip directly across the VIN or VOUT and GND terminals as shown in Figure 2.

With power off, connect the input power supply to VIN and GND.
Keep the load set to 0A or disconnected.
Turn the input power source on and slowly increase the input voltage.
NOTE: Make sure that the input voltage VIN does not exceed 72V.
Set the input voltage to 48V and check for the proper output voltage of 12V. If there is no output, temporarily disconnect the load to make sure that the load is not set too high.
Once the proper output voltage is established, adjust the load, and observe the output voltage regulation, ripple voltage, efficiency, and other parameters.

ANALOG DEVICES DC2995A High Frequency Step Down Supply GaN
FETs ANALOG DEVICES DC2995A High
Frequency Step Down Supply GaN FETs - Output Ripple

QUICK START PROCEDURE

Changing the Output Voltage
To change the output voltage from the programmed 12V, change the voltage setting resistors connected to LTC7891 FB pin (see Schematic Diagram section). Also, change all the power components required to meet the desired output voltage.
Converter Efficiency and Output Current
Typical performance of DC2995A is shown in Figure 3.
The efficiency is high even at light loads thanks to Burst Mode® operation. ANALOG DEVICES DC2995A High Frequency Step Down Supply GaN FETs -
Output Current

Figure 3. The 12V Output Efficiency is 96.1% with 20A Load

Output Load Step Response
The load step response of DC2995A is dependent on the amount and type of output caps used. For higher load steps more output capacitance can be added to keep the voltage transients at the desired level. The 10A load step transients with 48V input are shown in Figure 4. Other types of low ESR and high value capacitors can be used if space is available to reduce load transients to desired level.

Figure 4. The LTC7891 Has Good Load Step Response with Small Output Capacitors

Start-Up and Soft-Start Function
The DC2995A features a soft-start circuit that ramps the output voltage up in monotonic fashion as shown in Figure 5. The soft-start circuit also prevents output voltage overshoot when output voltage ramp reaches regulation.
When RUN pin is enabled, the output voltage will start ramping up after 1ms delay that is required for INTVCC pin to reach the internal UVLO level.

Figure 5. The DC2995A Ramps the Output Slowly at Start-Up without Output Voltage Overshoot

Thermal Performance
The LTC7891 features excellent thermal performance due to high efficiency of synchronous buck circuit. The temperature rises of LTC7891 with 48V input and 20A load is shown in Figure 6.
The six-layer PCB layout features solid copper planes that provide heat spreading across the whole board. ANALOG DEVICES DC2995A High Frequency Step
Down Supply GaN FETs - whole board

Figure 6. The LTC7891 Has Only 54.2°C Temperature Rise with
48V Input, 12V Output and 20A Load. (TA = 25°C, No Cooling Fan)

PARTS LIST

ITEM| QTY| REFERENCE| PART DESCRIPTION| MANUFACTURER/PART NUMBER
---|---|---|---|---

Required Circuit Components

1	1	C1	CAP., 4.7µF, X5R, 25V, 10%, 0603	MURATA, GRM188R61E475KE11D
2	3	C2, C3, C17	CAP., 0.1µF, X7R, 25V, 10%, 0603	AVX, 06033C104KAT2A
3	1	C7	CAP., 1000pF, X7R, 25V, 10%, 0603	AVX, 06033C102KAT2A
4	2	C10, C24	CAP., 100pF, C0G, 25V, 10%, 0603	AVX, 06033A101KAT2A
5	1	C14	CAP., 4700pF, C0G/NP0, 50V, 5%, 0603	AVX, 06035A472JAT2A
6	1	C15	CAP., 1µF, X5R, 50V, 10%, 0603, AEC-Q200	MURATA,

Additional Demo Board Circuit Components

1| 0| C16| CAP., OPTION, 0603|
---|---|---|---|---
2| 0| CIN13-CIN16| CAP., 10µF, X7S, 100V, 10%, 1210| MURATA, GRM32EC72A106KE05L
3| 0| COUT6, COUT18| CAP., OPTION, 7343|
4| 0| D4| DIODE, SCHOTTKY, 100V, 12A, SO-8FL, AEC-101| ON SEMICONDUCTOR, NTS12100EMFST1G
5| 0| D5| DIODE, SCHOTTKY BARRIER 100V 200mA SOD-323| ON SEMICONDUCTOR, NSR02100HT1G
6| 0| R30, R31, R34, R38, R53, R61, R70-R77, R80, R82| RES., OPTION, 0603|
7| 0| R69| RES., OPTION, 2512|
8| 1| SW1| SWITCH SLIDE DPDT 300MA 6V THROUGH HOLE| C&K, JS202011CQN
9| 4| J1, J2, J5, J6| EVAL BOARD STUD HARDWARE SET, #10-32| ANALOG DEVICES, 720-0010
10| 0| L1| IND., OPTION, 3.6µH, PWR, SHIELDED, 20%, 30A, 1.82mΩ, 19.69mm × 19.56mm × 12.95mm, SER2013, AEC-Q200| COILCRAFT, SER2013-362MLB

SCHEMATIC DIAGRAM

ANALOG DEVICES DC2995A High Frequency Step Down Supply GaN FETs - UVLO
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ESD Caution

ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.

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