Purpose
The RT2859BH are high-performance 650kHz 3A step-down regulators with internal power switches and synchronous rectifiers. This document explains the function and use of the RT2859BH evaluation board (EVB), and provides information to enable operation, modification of the evaluation board and circuit to suit individual requirements.
Introduction
General Product Information
The RT2859BH are high-performance 650kHz 3A step-down regulators with internal power switches and synchronous rectifiers. The feature quick transient response using Advanced Constant On-Time (ACOTTM) control architecture that provides stable operation with small ceramic output capacitors and without complicated external compensation, among other benefits. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V. The proprietary ACOTTM control improves upon other fast response constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. The RT2859BH are stable with and optimized for ceramic output capacitors. With internal 70mΩ switches and 70mΩ synchronous rectifiers, the RT2859BH display excellent efficiency and good behavior across a range of applications, especially for low output voltages and low duty cycles. Cycle-bycycle current limit, input under-voltage lock-out, externallyadjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions. The RT2859BH is available in WQFN-16L 3x3 package, with exposed thermal pads.
Product Feature
-
Fast Transient Response
-
Steady 650kHz Switching Frequency at all Load Current
-
3A Output Current
-
Advanced Constant On-Time (ACOT™) Control
-
Optimized for Ceramic Output Capacitors
-
4.5V to 18V Input Voltage Range
-
Internal 70mΩ Switch and 70mΩ Synchronous Rectifier
-
0.765V to 7V Adjustable Output Voltage
-
Externally-adjustable, Pre-biased Compatible Soft-Start
-
Cycle-by-Cycle Current Limit
-
Optional Output Discharge Function
-
With Hiccup Mode Output Over- and Under-voltage Shut-down protection
-
Input Under-Voltage Lockout
-
Thermal Shutdown
Key Performance Summary Table
|
Key Features
|
Evaluation Board Number : PCB033_V1
|
|
Input Voltage Range
|
4.5V to 18V
|
|
Max Output Current
|
3A
|
|
Default Output Voltage
|
1.05V
|
|
Default Marking & Package Type
|
RT2859BHGQW, WQFN-16L 3x3
|
|
Operation Frequency
|
Fixed 650kHz
|
Bench Test Setup Conditions
Headers Description and Placement
Please carefully inspect the EVB IC and external components, comparing them to the following Bill of Materials, to ensure that all components are installed and undamaged. If any components are missing or damaged during transportation, please contact the distributor or send e-mail to evb_service@richtek.com.
Test Points
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)
|
|
VIN
|
Input voltage
|
Power input.
|
|
EN
|
Enable test point
|
Externally pulled high to enable and pulled low to disable this chip. It is internally pulled up to high when the pin is floating.
|
|
GND
|
Ground
|
The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation.
|
|
VREG5
|
Internal Regulator Output
|
Internal Regulator Output. Connect a 1μF capacitor to GND to stabilize output voltage.
|
|
SS
|
Soft-Start Control
|
Connect an external capacitor between this pin and GND to set the soft-start time.
|
|
PG
|
Power good test point
|
Output of power good indicator.
|
|
BOOT
|
Bootstrap supply test point
|
Bootstrap supply for High-Side gate driver. Connect a capacitor between the BOOT and SW pins.
|
|
SW
|
Switch node test point
|
Connect this pin to an external L-C filter.
|
Power-up & Measurement Procedure
1. Apply a 12V nominal input power supply (4.5< VIN < 18V) to the VIN and GND terminals.
2. Set the jumper at JP2 to connect terminals 2 and 3, connecting EN to enable operation.
3. Set the jumper at JP1 to connect terminals 1 and 2, power VCC pin by VIN voltage source.
4. Verify the output voltage (approximately 1.05V) between VOUT and GND.
5. Connect an external load up to 3A to the VOUT and GND terminals and verify the output voltage and current.
Output Voltage Setting
Set the output voltage with the resistive divider (R2, R3) between VOUT and GND with the midpoint connected to FB. The output is set by the following formula :
Schematic, Bill of Materials & Board Layout
EVB Schematic Diagram
Bill of Materials
|
Reference
|
Qty
|
Part Number
|
Description
|
Package
|
Manufacture
|
|
U1
|
1
|
RT2859BHGQW
|
DC/DC Converter
|
WQFN-16L 3x3
|
RICHTEK
|
|
C2, C6, C8, C12
|
4
|
C1608X7R1H104KT000N
|
0.1μF/50V/X7R
|
C-0603
|
TDK
|
|
C3, C4
|
2
|
GRM31CR71E106KA12L
|
10μF/25V/X7R
|
C-1206
|
MURATA
|
|
C5
|
1
|
C2012X7R1H105KT
|
1μF/50V/X7R
|
C-0805
|
TDK
|
|
C7
|
1
|
0603B332K500
|
3.3nF/50V/X7R
|
C-0603
|
WALSIN
|
|
C9,C10
|
2
|
C3225X5R1E226MT
|
22μF/25V/X7R
|
C-1210
|
TDK
|
|
C1, C11, C13,
C14, R6, R7
|
6
|
|
NA
|
|
|
|
L1
|
1
|
NR8040T1R4N
|
1.4µH/7A
|
8 x 8 x 4 mm
|
TAIYO YUDEN
|
|
R1
|
1
|
0603 JUMP
|
0Ω
|
R-0603
|
WALSIN
|
|
R2
|
1
|
0603 8K25 1%
|
8.25k
|
R-0603
|
WALSIN
|
|
R3
|
1
|
0603 22K1 1%
|
22.1k
|
R-0603
|
WALSIN
|
|
R4, R5
|
2
|
0603 100K 1%
|
100k
|
R-0603
|
WALSIN
|
PCB Layout
Top View (1st layer)
PCB Layout—Inner Side (2nd Layer)
PCB Layout—Inner Side (3rd Layer)
Bottom View (4th Layer)