Richtek RT8004GCP, RT8004GQV, RT8004PCP, RT8004PQV Schematic [ru]
Loading...
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.
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 requirements of IPC/JEDEC J-STD-020.
`Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
For marking information, contact our sales representative directly or through a Richtek distributor located in your area.
Features
zHigh Efficiency : Up to 95%
zLow Quiescent Current : 100μA
zLow RDS(ON) Internal Switches : 75mΩ
zProgrammable Frequency : 300kHz to 4MHz
zNo Schottky Diode Required
z0.8V Reference Allows Low Output Voltage
zLow Dropout Operation : 100% Duty Cycle
zSynchronizable Switching Frequency
zPower Good Output Voltage Monitor
zOver Temperature Protection
zThermally Enhanced TSSOP-16 (Exposed Pad) and 16-Lead VQFN 4x4 Packages
zRoHS Compliant and 100% Lead (Pb)-Free
Applications
zPortable Instruments
zBattery-Powered Equipment
zNotebook Computers
zDistributed Power Systems
zIP Phones
zDigital Cameras
Pin Configurations
(TOP VIEW)
|
PGOOD |
VDD |
PVDD |
LX |
|
|
|
16 15 14 13 |
|
|
|||
COMP |
1 |
|
|
|
12 |
LX |
FB |
2 |
GND |
|
11 |
PGND |
|
RT |
3 |
|
10 |
PGND |
||
|
17 |
|||||
SYNC |
4 |
|
9 |
LX |
||
|
|
|
||||
|
5 |
6 |
7 |
8 |
|
|
|
EN/SS |
GND |
PVDD |
LX |
|
|
|
VQFN-16L 4x4 |
|
||||
VDD |
|
|
16 |
PVDD |
|
PGOOD |
2 |
|
15 |
LX |
|
COMP |
3 |
|
14 |
LX |
|
FB |
4 |
GND |
13 |
PGND |
|
RT |
5 |
12 |
PGND |
||
|
|||||
SYNC |
6 |
17 11 |
LX |
||
EN/SS |
7 |
|
10 |
LX |
|
GND |
8 |
|
9 |
PVDD |
|
TSSOP-16 (Exposed Pad)
DS8004-07 March 2011 |
www.richtek.com |
1
RT8004
Typical Application Circuit
VIN
|
|
|
|
2.65V to 5.5V |
|
RPG |
|
|
47uF |
100k |
|
|
||
VDD |
|
|
||
|
|
|
|
|
PGOOD |
|
RT8004 |
C1 |
|
|
PGOOD |
R1 |
||
|
|
22pF |
||
CTH |
RTH |
510k |
||
|
|
|
||
1000pF |
|
L1 |
|
|
10k |
COMP |
|
||
|
|
1uH |
VOUT |
|
|
R2 |
|
LX |
|
|
|
2.5V/3A |
||
|
240k |
FB |
|
|
|
|
|
|
|
|
ROCS |
|
|
COUT |
|
309k |
RT |
|
47uF |
|
|
PVDD |
|
|
|
|
|
|
|
External Clock |
SYNC |
CIN1 |
|
|
RSS |
|
|
10uF |
|
4.7M |
|
EN/SS |
PVDD |
|
|
CSS |
|
||
|
|
|
CIN2 |
|
|
470pF |
|
|
|
|
GND |
10uF |
||
|
|
|||
|
|
PGND |
|
|
|
|
|
|
|
Functional Pin Description
Pin No. |
Pin Name |
Pin Function |
|
||
RT8004PCP |
RT8004PQP |
|
|||
1 |
15 |
VDD |
Signal Input Supply. Decouple this pin to GND with a |
capacitor. |
|
Normally VDD is equal to PVDD. |
|
||||
|
|
|
|
||
2 |
16 |
PGOOD |
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 |
||
3 |
1 |
COMP |
increases with this control voltage. Connect external compensation |
||
|
|
|
elements to this pin to stabilize the control loop. |
|
|
4 |
2 |
FB |
Feedback Pin. Receives the feedback voltage from a resistive divider |
||
connected across the output. |
|
||||
|
|
|
|
||
|
|
|
|
||
5 |
3 |
RT |
Oscillator Resistor Input. Connecting a resistor to ground from this pin |
||
sets the switching frequency. |
|
||||
|
|
|
|
||
|
|
|
|
||
|
|
|
External Clock Synchronization Input. The internal oscillator can be |
||
6 |
4 |
SYNC |
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 |
||
7 |
5 |
EN/SS |
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. |
|
|
8, |
6, |
|
Signal Ground. All small-signal components, compensation components |
||
Exposed Pad |
Exposed Pad |
GND |
and the exposed pad on the bottom side of the IC should connect to this |
||
(17) |
(17) |
|
ground, which in turn connects to PGND at one point. |
|
|
9, 16 |
7, 14 |
PVDD |
Power Input Supply. Decouple this pin to PGND with a capacitor. |
||
10,11, |
8, 9, 12, 13 |
LX |
Internal Power MOSFET Switches Output. Connect this |
pin to the |
|
14, 15 |
inductor. |
|
|||
|
|
|
|||
12, 13 |
10, 11 |
PGND |
Power Ground. Connect this pin close to the terminal of CIN and COUT. |
||
|
|
|
|
|
|
|
|
|
|
|
|
www.richtek.com |
|
DS8004-07 |
March 2011 |
||
2
RT8004
Function Block Diagram
|
|
|
RT |
|
|
|
|
|
|
|
|
|
|
|
ISEN |
|
PVDD |
SYNC |
ExtSyn |
Oscillator |
|
Slope Com |
|
|
|
|
COMP |
|
|
|
|
|
|
|
|
|
0.8V |
|
Output |
|
|
OC |
|
|
|
EA |
|
|
Limit |
|
LX |
||
FB |
|
Clamp |
|
|
|
|
||
|
|
|
|
|
Driver |
|||
|
|
|
|
|
|
|
|
|
EN/SS |
Ext_SS |
|
SD |
0.9V |
|
Control |
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
||
|
Int_SS |
|
|
|
|
Logic |
|
|
|
|
|
0.7V |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
NISEN |
PGND |
|
|
|
|
0.4V |
|
|
|
|
|
|
|
|
|
|
NMOS I Limit |
|
|
|
|
|
|
|
|
|
|
|
|
POR |
POR |
|
0.8V |
|
|
PGOOD |
|
|
|
|
|
|
||||
|
|
|
|
|
|
|||
|
|
|
|
BG |
VREF |
OTP |
|
|
|
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 ontime. 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 RDS(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 |
DS8004-07 March 2011 |
4
|
|
|
|
|
|
RT8004 |
||||
Absolute Maximum Ratings |
(Note 1) |
|
|
|
|
|
|
|
||
z Supply Input Voltage ---------------------------------------------------------------------------------------------- |
|
|
|
|
−0.3V to 6V |
|
|
|||
z LX Pin Switch Voltage -------------------------------------------------------------------------------------------- |
|
|
|
|
−0.3V to (PVDD + 0.3V) |
|||||
z Other I/O Pin Voltages ------------------------------------------------------------------------------------------- |
|
|
|
|
−0.3V to (VDD + 0.3V) |
|||||
z Power Dissipation, PD @ TA = 25°C |
|
|
|
|
|
|
|
|
|
|
TSSOP-16----------------------------------------------------------------------------------------------------------- |
|
|
|
|
2.66W |
|
|
|
|
|
VQFN-16L 4x4 ----------------------------------------------------------------------------------------------------- |
|
|
|
|
2.315W |
|
|
|||
z Package Thermal Resistance (Note 2) |
|
|
|
|
|
|
|
|
|
|
TSSOP-16, θJA ----------------------------------------------------------------------------------------------------- |
|
|
|
|
47°C/W |
|
|
|||
VQFN-16L 4x4, θJA ------------------------------------------------------------------------------------------------ |
|
|
|
|
54°C/W |
|
|
|||
VQFN-16L 4x4, θJC ----------------------------------------------------------------------------------------------- |
|
|
|
|
7°C/W |
|
|
|
|
|
z Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- |
|
|
|
260°C |
|
|
|
|
||
z Junction Temperature --------------------------------------------------------------------------------------------- |
|
|
|
|
150°C |
|
|
|
|
|
z Storage Temperature Range ------------------------------------------------------------------------------------ |
|
|
|
|
−65°C to +150°C |
|||||
z ESD Susceptibility (Note 3) |
|
|
|
|
|
|
|
|
|
|
HBM (Human Body Mode) -------------------------------------------------------------------------------------- |
|
|
|
|
2kV |
|
|
|
|
|
MM (Machine Mode) ---------------------------------------------------------------------------------------------- |
|
|
|
|
200V |
|
|
|
|
|
Recommended Operating Conditions (Note 4) |
|
|
|
|
|
|
|
|||
z Supply Input Voltage ---------------------------------------------------------------------------------------------- |
|
|
|
|
2.65V to 5.5V |
|
|
|||
z Ambient Temperature Range ------------------------------------------------------------------------------------ |
|
|
|
|
−40°C to 85°C |
|
|
|||
z Junction Temperature Range ------------------------------------------------------------------------------------ |
|
|
|
|
−40°C to 125°C |
|||||
Electrical Characteristics |
|
|
|
|
|
|
|
|
|
|
(VDD = 3.3V, TA = 25°C, unless otherwise specified) |
|
|
|
|
|
|
|
|||
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
|
Max |
|
Unit |
|
|
|
|
|
|
|
|
|
|
|
|
|
Input Voltage Range |
VDD |
|
|
2.65 |
-- |
|
5.5 |
|
V |
|
Feedback Voltage |
VFB |
|
(Note 5) |
0.784 |
0.8 |
|
0.816 |
|
V |
|
|
|
|
|
|
|
|
|
|
|
|
Feedback Leakage Current |
IFB |
|
|
-- |
-- |
|
0.4 |
|
μA |
|
|
|
|
Active, VFB = 0.78V, |
180 |
400 |
|
520 |
|
μA |
|
Input DC Bias Current |
|
|
Not switching |
|
|
|
||||
|
|
|
|
|
|
|
|
|
||
|
|
|
Shutdown, VEN < 0.1V (Note 5) |
-- |
-- |
|
1 |
|
μA |
|
Reference Voltage Line Regulation |
|
|
VIN = 2.7V to 5.5V (Note 5) |
-- |
0.04 |
|
0.5 |
|
%/V |
|
|
|
|
Measured in Servo Loop, |
|
|
|
|
|
% |
|
Output Voltage Load Regulation |
|
|
VCOMP = 1.2V to 1.6V |
-- |
0.05 |
|
+/-0.2 |
|
|
|
|
|
|
(Note 5) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Power Good |
|
|
|
|
|
|
|
|
|
|
Power Good Range |
|
|
|
-- |
±12.5 |
|
±15 |
|
% |
|
|
|
|
|
|
|
|
|
|
|
|
Power Good Pull-Down Resistance |
|
|
|
-- |
-- |
|
120 |
|
Ω |
|
|
|
|
|
|
|
|
|
|
|
|
Switching Frequency |
fOSC |
|
ROSC = 309k |
0.8 |
1 |
|
1.2 |
|
MHz |
|
|
Switching Frequency Range |
0.3 |
-- |
|
4 |
|
MHz |
|
||
|
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
|
|
Sync Frequency Range |
|
|
(Note 6) |
0.3 |
-- |
|
4 |
|
MHz |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
To be continued |
|||
|
|
|
|
|
|
|
|
|
|
|
DS8004-07 March 2011 |
|
|
|
|
|
|
www.richtek.com |
|||
5