The RT6255A is a synchronous step-down converter with Advanced Constant On-Time (ACOT™) mode control. with the input voltage range from 4.5V to 18V and provides 5A output current. This document explains the function and use of the RT6255A evaluation board (EVB), and provides information to enable operation, modification of the evaluation board and circuit to suit individual requirements. General Product Information
The RT6255A is a high-efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 5A output current from a 4.5V to 18V input supply.The RT6255A adopts ACOT architecture to allow the transient response to be improved and keep in constant frequency. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. Fault conditions also include output under voltage protection and thermal shutdown.
Key Performance Summary Table
Key Features
Evaluation Board Number: PCB074_V1
Default Input Voltage
12V
Max Output Current
5A
Default Output Voltage
5V
Default Marking & Package Type
RT6255AHGJ6F, TSOT-23-6 (FC)
Operation Frequency
Steady 500kHz at all loads
Carefully inspect all the components used in the EVB according to the following Bill of Materials table, and then make sure all the components are undamaged and correctly installed. If there is any missing or damaged component, which may occur during transportation, please contact our distributors or e-mail us at evb_service@richtek.com.
The EVB is provided with the test points and pin names listed in the table below.
Test point/
Pin name
Signal
Comment (expected waveforms or voltage levels on test points)
FB
Feedback Voltage Input
This pin is used to set the desired output voltage via an external resistive divider. The feedback reference voltage is 0.6V typically.
VIN
Input voltage
Power Input. Supplies the power switches of the device.
GND
Ground
This is the power return for the IC.
BOOT
Bootstrap
Bootstrap Supply for High-Side Gate Driver. Connect a 0.1µF ceramic capacitor from LX to BOOT to power the high-side switch.
LX
Switch node test point
Connect the output LC filter from LX to the output load.
EN
Enable Control Input
Floating this pin or connecting this pin to logic high can enable the device and connecting this pin to GND can disable the device.
1. Apply a 12V nominal input power supply (4.5V < VIN < 18V) to the VIN and GND terminals.
2. Set the jumper at JP1 to connect terminals 2 and 3, connecting EN to VIN through resistor R30, to enable operation.
3. Verify the output voltage (approximately 5V) between VOUT and GND.
4. Connect an external load up to 5A to the VOUT and GND terminals and verify the output voltage and current.
Set the output voltage with the resistive divider (R1, R2) between VOUT and GND with the midpoint connected to FB. The output is set by the following formula:
VOUT = VFB x (1 + R1 / R2)
Reference
Qty
Part Number
Description
Package
Manufacturer
U1
1
RT6255AHGJ6F
DC-DC Converter
TSOT-23-6 (FC)
RICHTEK
C7, C9
2
C3216X5R1H106KT000N
10µF/50V/X5R/1206
C-1206
TDK
C8, C10, CB
3
C1608X7R1H104KT000N
0.1µF/50V/X7R/0603
C-0603
CFF
0603N470J500
47pF/50V/X7R/0603
WALSIN
C11, C12
C3225X5R1E226MT
22µF/25V/X5R/1210
C-1210
C32
NC
L1
710-7443340470
4.7µH
L-GSC104
Wurth Elektronik
L2
L-NR8040
R1
0603T-1-147K
147k/0603
R-0603
旺詮
R2
0603T-1-20K
20k/0603
Rt
0603 5K10 1%
5k1/0603
R30
0603 100K 1%
100k/0603
R31
Top View (1st layer)
PCB Layout—Inner Side (2nd Layer)
PCB Layout—Inner Side (3rd Layer)
Bottom View (4th Layer)
