Step-Down Converter. RT2875B Datasheet

RT2875B Converter. Datasheet pdf. Equivalent

RT2875B Datasheet
Recommendation RT2875B Datasheet
Part RT2875B
Description Synchronous Step-Down Converter
Feature RT2875B; ® RT2875A/B 3A, 36V, Synchronous Step-Down Converter General Description The RT2875A/B is a high e.
Manufacture Richtek
Datasheet
Download RT2875B Datasheet




Richtek RT2875B
®
RT2875A/B
3A, 36V, Synchronous Step-Down Converter
General Description
The RT2875A/B is a high efficiency, current-mode
synchronous DC/DC step-down converter that can deliver
up to 3A output current over a wide input voltage range
from 4.5V to 36V. The device integrates 95mΩ high-side
and 70mΩ low-side MOSFETs to achieve high conversion
efficiency. The current-mode control architecture
supports fast transient response and simple external
compensation. A cycle-by-cycle current limit function
provides protection
against shorted output and an external soft-start eliminates
input current surge during start-up. The RT2875A/B
provides complete protection functions such as input
under-voltage lockout, output under-voltage protection,
over-current protection and thermal shutdown.
The RT2875A/B is available in the thermal enhanced
TSSOP-14 (Exposed Pad) package.
Pin Configurations
(TOP VIEW)
SW
SW
PGND
RT/SYNC
AGND
RLIM
FB
14
2 13
3 12
4 PGND 11
5 10
6 15 9
78
BOOT
VIN
VIN
PGOOD
EN
SS
COMP
TSSOP-14 (Exposed Pad)
Features
3A Output Current
Internal N-MOSFETs
Current Mode Control
Adjustable Switching Frequency : 300kHz to 2.1MHz
Adjustable Current Limit : 1.5A to 6A
Synchronous to External Clock : 300kHz to 2.1MHz
Adjustable Output Voltage from 0.6V to 24V
High Efficiency Up to 95%
Stable with Low ESR Ceramic Output Capacitors
Cycle-by-Cycle Current Limit
Input Under-Voltage Lockout
Output Under-Voltage Protection
Thermal Shutdown
AEC-Q100 Grade 2 Certification
RoHS Compliant and Halogen Free
Applications
Point of Load Regulator in Distributed Power Systems
Digital Set Top Boxes
Broadband Communications
Vehicle Electronics
Simplified Application Circuit
VIN
Enable
PGOOD
CIN
RLIM ROSC
VIN BOOT
RT2875A/B
SW
EN
PGOOD
RLIM
FB
RT/SYNC COMP
SS
AGND PGND
CBOOT L
RCOMP CCOMP
CSS
VOUT
R1
COUT
R2
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS2875A/B-04 August 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1



Richtek RT2875B
RT2875A/B
Ordering Information
RT2875A/B
Package Type
CP: TSSOP-14 (Exposed Pad)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
AQ : Latched UVP
BQ : Hiccup Mode UVP
Richtek products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
RT2875AQGCP
RT2875AQ
GCPYMDNN
RT2875AQGCP : Product Number
YMDNN : Date Code
RT2875BQGCP
RT2875BQ
GCPYMDNN
RT2875BQGCP : Product Number
YMDNN : Date Code
Functional Pin Description
Pin No.
Pin Name
Pin Function
1, 2 SW
Switch Node. Connect to external L-C filter.
3,
15 (Exposed Pad)
PGND
4 RT/SYNC
5 AGND
Power Ground. The exposed pad must be soldered to a large PCB and
connected to PGND for maximum power dissipation.
Oscillator Resistor and External Frequency Synchronization Input. Must connect
a resistor from this pin to GND to set the switching frequency. If SYNC clock is
requested, connect an external clock to change the switching frequency.
Analog Ground.
6
RLIM
Current Limit Setting. Connect a resistor from this pin to GND to set the current
limit value.
7 FB
Feedback Voltage Input. The pin is used to set the output voltage of the
converter to regulate to the desired via a resistive divider. Feedback reference =
0.6V.
Compensation Node. COMP is used to compensate the regulation control loop.
8
COMP
Connect a series RC network from COMP to GND. In some cases, an additional
capacitor from COMP to GND is required.
9
SS
Soft-Start Time Setting. Connect a capacitor from SS to GND to set the
soft-start period.
10 EN
Enable Control Input. High = Enable.
11 PGOOD Power Good Indicator Output.
12, 13
14
VIN
BOOT
Power Input. Support 4.5V to 36V input voltage. Must bypass with a suitable
large ceramic capacitor at this pin.
Bootstrap Supply for High-Side Gate Driver. Connect a 0.1F ceramic capacitor
between the BOOT and SW pins.
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS2875A/B-04 August 2015



Richtek RT2875B
Function Block Diagram
PGOOD
VIN
RT2875A/B
EN
FB
AGND
6k
1.5V
3.8V
-
+
Shutdown
Comparator
+
0.55V
0.3V
-
PGOOD
Comparator
+
Logic &
Protection
Control
-
UV
Comparator
-
0.6V +EA
+
6µA Oscillator
UVLO
Internal
Regulator
BOOT
UVLO
Power
Stage &
Deadtime
Control
HS Switch
Current
Comparator
Slop
Compensation
LS Switch
Current
Comparator
Current
Sense
Current
Sense
BOOT
SW
PGND
SS COMP RT/SYNC
RLIM
Operation
The RT2875A/B is current-mode synchronous step-down
converter. In normal operation, the high-side N-MOSFET
is turned on when the S-R latch is set by the oscillator
and is turned off when the current comparator resets the
S-R latch. While the high-side N-MOSFET is turned off,
the low-side N-MOSFET is turned on to conduct the
inductor current until next cycle begins.
Error Amplifier
The error amplifier adjusts its output voltage by comparing
the feedback signal (VFB) with the internal 0.6V reference.
When the load current increases, it causes a drop in the
feedback voltage relative to the reference, and then the
error amplifier's output voltage rises to allow higher inductor
current to match the load current.
Switching Frequency
The switching frequency can be set by using extra resister
RT or external clock. Switching frequency range is from
300kHz to 2.1MHz.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high-
side gate driver.
Enable
The converter is turned on when the EN pin is higher than
1.6V. When the EN pin is lower than 0.4V, the converter
will enter shutdown mode and reduce the supply current
lower than 10μA.
Soft-Start (SS)
In order to prevent the converter output voltage from
overshooting during the startup period, the soft-start
function is necessary. The soft-start time is adjustable
by an external capacitor.
Copyright ©2015 Richtek Technology Corporation. All rights reserved.
DS2875A/B-04 August 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3







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