RT8004
3A, 4MHz, Synchronous Step-Down Regulator
General Description
The RT8004 is a high efficiency synchronous, step-down
DC/DC converter. Its input voltage range is from 2.65V to
5.5V and provides an adjustable regulated output voltage
from 0.8V to 5V while delivering up to 3A of output current.
The internal power switch with 75mΩ on-resistance
increases efficiency and eliminates the need for an external
Schottky diode. Switching frequency is set by an external
resistor or can be synchronized to an external clock. 100%
duty cycle provides low dropout operation extending
battery life in portable systems. External compensation
allows the transient response to be optimized over a wide
range of loads and output capacitors.
The RT8004 operates in Forced Continuous Mode which
reduces noise and RF interference. 100% duty cycle in
Low Dropout Operation further maximize battery life.
Features
High Efficiency : Up to 95%
Low Quiescent Current : 100μA
μ
Ω
Low R
DS(ON)
Internal Switches : 75mΩ
Programmable Frequency : 300kHz to 4MHz
No Schottky Diode Required
0.8V Reference Allows Low Output Voltage
Low Dropout Operation : 100% Duty Cycle
Synchronizable Switching Frequency
Power Good Output Voltage Monitor
Over Temperature Protection
Thermally Enhanced TSSOP-16 (Exposed Pad) and
16-Lead VQFN 4x4 Packages
RoHS Compliant and 100% Lead (Pb)-Free
Applications
Portable Instruments
Battery-Powered Equipment
Notebook Computers
Distributed Power Systems
IP Phones
Digital Cameras
Ordering Information
RT8004
Package Type
CP : TSSOP-16 (Exposed Pad)
QV : VQFN-16L 4x4 (V-Type)
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Note :
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.
Pin Configurations
(TOP VIEW)
PGOOD
VDD
PVDD
LX
16 15 14 13
COMP
FB
RT
SYNC
1
2
3
4
GND
17
5 6 7 8
EN/SS
GND
PVDD
LX
12
11
10
9
LX
PGND
PGND
LX
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
VQFN-16L 4x4
VDD
PGOOD
COMP
FB
RT
SYNC
EN/SS
GND
16
15
14
13
GND
12
17 11
10
9
PVDD
LX
LX
PGND
PGND
LX
LX
PVDD
2
3
4
5
6
7
8
TSSOP-16 (Exposed Pad)
DS8004-07 March 2011
www.richtek.com
1
RT8004
Typical Application Circuit
V
IN
2.65V to 5.5V
RPG
100k
PGOOD
CTH RTH
1000pF 10k
R2
240k
R
OCS
309k
External Clock
R
SS
4.7M
C
SS
470pF
47uF
VDD
RT8004
PGOOD
COMP
LX
FB
RT
SYNC
R1
510k
L1
1uH
C1
22pF
V
OUT
2.5V/3A
C
OUT
47uF
PVDD
C
IN1
10uF
PVDD
C
IN2
10uF
PGND
EN/SS
GND
Functional Pin Description
Pin No.
Pin Name
RT8004PCP RT8004PQP
1
2
3
4
5
6
15
16
1
2
3
4
VDD
PGOOD
COMP
FB
RT
SYNC
Pin Function
Signal Input Supply. Decouple this pin to GND with a capacitor.
Normally VDD is equal to PVDD.
Power Good Indicator. Open-drain logic output that is pulled to ground
when the output voltage is not within ±12.5% of regulation point.
Error Amplifier Compensation Pin. The current comparator threshold
increases with this control voltage. Connect external compensation
elements to this pin to stabilize the control loop.
Feedback Pin. Receives the feedback voltage from a resistive divider
connected across the output.
Oscillator Resistor Input. Connecting a resistor to ground from this pin
sets the switching frequency.
External Clock Synchronization Input. The internal oscillator can be
synchronized to an external clock applied to this pin. If not use, please
connect this pin to VDD or GND.
Enable Control and Soft-Start Input. Forcing this pin below 0.5V shuts
down the RT8004. In shutdown all functions are disabled drawing < 1μA
of supply current. A capacitor to ground from this pin sets the ramp time
to full output current.
Signal Ground. All small-signal components, compensation components
and the exposed pad on the bottom side of the IC should connect to this
ground, which in turn connects to PGND at one point.
Power Input Supply. Decouple this pin to PGND with a capacitor.
Internal Power MOSFET Switches Output. Connect this pin to the
inductor.
Power Ground. Connect this pin close to the terminal of C
IN
and C
OUT
.
DS8004-07 March 2011
7
5
EN/SS
8,
6,
Exposed Pad Exposed Pad GND
(17)
(17)
9, 16
10,11,
14, 15
12, 13
www.richtek.com
2
7, 14
PVDD
8, 9, 12, 13 LX
10, 11
PGND
RT8004
Function Block Diagram
RT
ISEN
SYNC
ExtSyn
Oscillator
Slope Com
PVDD
COMP
0.8V
FB
EA
Output
Clamp
OC
Limit
Driver
Ext_SS
Int_SS
LX
EN/SS
SD
0.9V
0.7V
Control
Logic
NISEN
0.4V
NMOS I Limit
0.8V
BG
V
REF
OTP
PGND
PGOOD
POR
POR
VDD
GND
Operation
Main Control Loop
The RT8004 is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation,
the internal
top power switch (P-MOSFET) is turned on at the beginning of each clock cycle. Current in the inductor
increases until the peak inductor current reach the value defined by the voltage on the COMP pin. The error amplifier
adjusts the voltage on the COMP pin by comparing the feedback signal from a resistor divider on the FB pin with an
internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative to the
reference. The error amplifier raises the COMP voltage until the average inductor current matches the new load current.
When the top power MOSFET shuts off, the synchronous power switch (N-MOSFET) turns on until either the bottom
current limit is reached or the beginning of the next clock cycle. The bottom current limit is set at
−2A.
The operating frequency is set by an external resistor connected between the RT pin and ground. The practical switching
frequency can range from 300kHz to 4MHz.
Power Good comparators will pull the PGOOD output low if the output voltage comes out of regulation by 12.5%. In an
over voltage condition, the top power MOSFET is turned off and the bottom power MOSFET is switched on until either
the overvoltage condition clears or the bottom MOSFET’ s current limit is reached.
Frequency Synchronization
The internal oscillator of the RT8004 can be synchronized to an external clock connected to the SYNC pin. The
frequency of the external clock can be in the range of 300kHz to 4MHz. For this application, the oscillator timing resistor
should be chosen to correspond to a frequency that is about 20% lower than the synchronization frequency.
DS8004-07 March 2011
www.richtek.com
3
RT8004
Dropout Operation
When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-
time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle eventually
reaching 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across
the internal P-MOSFET and the inductor.
Low Supply Operation
The RT8004 is designed to operate down to an input supply voltage of 2.65V. One important consideration
at low input
supply voltages is that the R
DS(ON)
of the P-MOSFET and N-MOSFET power switches increases. The user should
calculate the power dissipation when the RT8004 is used at 100% duty cycle with low input voltages to ensure that
thermal limits are not exceeded.
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant frequency architectures by preventing subharmonic oscillations at
duty cycles greater than 50%. It is accomplished internally by adding a compensating ramp to the inductor current
signal. Normally, the maximum inductor peak current is reduced when slope compensation is added. In the RT8004,
however, separated inductor current signals are used to monitor over current condition
and minimum peak current.
This
keeps the maximum output current and minimum peak current relatively constant regardless of duty cycle.
Short Circuit Protection
When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current
runaway detector is used to monitor inductor current. As current increasing beyond the control of current loop, switching
cycles will be skipped to prevent current runaway from occurring.
www.richtek.com
4
DS8004-07 March 2011
RT8004
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage ----------------------------------------------------------------------------------------------
−
0.3V to 6V
LX Pin Switch Voltage --------------------------------------------------------------------------------------------
−
0.3V to (PV
DD
+ 0.3V)
Other I/O Pin Voltages -------------------------------------------------------------------------------------------
−
0.3V to (V
DD
+ 0.3V)
Power Dissipation, P
D
@ T
A
= 25°C
TSSOP-16 ----------------------------------------------------------------------------------------------------------- 2.66W
VQFN-16L 4x4 ----------------------------------------------------------------------------------------------------- 2.315W
Package Thermal Resistance (Note 2)
TSSOP-16,
θ
JA
----------------------------------------------------------------------------------------------------- 47°C/W
VQFN-16L 4x4,
θ
JA
------------------------------------------------------------------------------------------------ 54°C/W
VQFN-16L 4x4,
θ
JC
----------------------------------------------------------------------------------------------- 7°C/W
Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- 260°C
Junction Temperature --------------------------------------------------------------------------------------------- 150°C
Storage Temperature Range ------------------------------------------------------------------------------------
−
65°C to +150°C
ESD Susceptibility (Note 3)
HBM (Human Body Mode) -------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ---------------------------------------------------------------------------------------------- 200V
Recommended Operating
Conditions
(Note 4)
Supply Input Voltage ---------------------------------------------------------------------------------------------- 2.65V to 5.5V
Ambient Temperature Range ------------------------------------------------------------------------------------
−
40°C to 85°C
Junction Temperature Range ------------------------------------------------------------------------------------
−
40°C to 125°C
Electrical Characteristics
(V
DD
= 3.3V, T
A
= 25°C, unless otherwise specified)
Parameter
Input Voltage Range
Feedback Voltage
Feedback Leakage Current
Input DC Bias Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Power Good
Power Good Range
Power Good Pull-Down Resistance
Switching Frequency
Sync Frequency Range
DS8004-07 March 2011
Symbol
V
DD
V
FB
I
FB
(Note 5)
Test Conditions
Min
2.65
0.784
--
Typ
--
0.8
--
400
--
0.04
0.05
Max
5.5
0.816
0.4
520
1
0.5
+/-0.2
Unit
V
V
μA
μA
μA
Active, V
FB
= 0.78V,
Not switching
Shutdown, V
EN
< 0.1V
V
IN
= 2.7V to 5.5V
Measured in Servo Loop,
V
COMP
= 1.2V to 1.6V
(Note 5)
(Note 5)
(Note 5)
180
--
--
--
%/V
%
--
--
f
OSC
R
OSC
= 309k
Switching Frequency Range
(Note 6)
0.8
0.3
0.3
±12.5
--
1
--
--
±15
120
1.2
4
4
%
Ω
MHz
MHz
MHz
To be continued
www.richtek.com
5
工业自动化与控制
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
