Richtek RT8251GQW, RT8251GSP Schematic [ru]
®
RT8251
5A, 24V, 570kHz Step-Down Converter
General Description
The RT8251 is a monolithic step-down switch mode converter with a built-in internal power MOSFET. It achieves 5A continuous output current over a wide input supply range with excellent load and line regulation. Current mode operation provides fast transient response and eases loop stabilization.
The RT8251 provides protection functions such as cycle-by-cycle current limiting and thermal shutdown. In shutdown mode, the regulator draws 25μA of supply current. Programmable soft-start minimizes the inrush supply current and the output overshoot at initial startup. The RT8251 requires a minimum number of external components. The RT8251 is available in WQFN-16L 3x3 and SOP-8 (Exposed Pad) packages.
Pin Configurations
(TOP VIEW)
|
VIN |
VIN |
SW |
SW |
|
|
|
16 |
15 |
14 |
13 |
|
|
VIN |
1 |
|
|
|
12 |
SW |
VIN |
2 |
GND |
|
11 |
SW |
|
VIN |
3 |
|
10 |
SW |
||
|
17 |
|||||
GND |
4 |
|
9 |
BOOT |
||
|
|
|
||||
|
5 |
6 |
7 |
8 |
|
|
|
FB |
COMP |
EN |
SS |
|
|
|
WQFN-16L 3x3 |
|
||||
BOOT |
|
8 |
SS |
VIN |
2 |
7 |
EN |
SW |
3 |
GND |
COMP |
6 |
|||
GND |
4 |
9 |
FB |
5 |
SOP-8 (Exposed Pad)
Features
zWide Operating Input Voltage Range : 4.75V to 24V
zAdjustable Output Voltage Range : 0.8V to 15V
zOutput Current up to 5A
z25μA Low Shutdown Current
zInternal Power MOSFET : 70mΩ
zHigh Efficiency up to 95%
z570kHz Fixed Switching Frequency
zStable with Low ESR Output Ceramic Capacitors
zThermal Shutdown Protection
zCycle-By-Cycle Over Current Protection
zRoHS Compliant and Halogen Free
Applications
zDistributed Power Systems
zBattery Charger
zDSL Modems
zPre-regulator for Linear Regulators
Ordering Information
RT8251 
Package Type
QW : WQFN-16L 3x3 (W-Type)
SP : SOP-8 (Exposed Pad-Option 1)
Lead Plating System
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.
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8251-04 February 2013 |
www.richtek.com |
|
1 |
RT8251
Marking Information
RT8251GQW |
|
RT8251GSP |
|
||
|
|
GE= : Product Code |
|
|
RT8251GSP : Product Number |
|
|
|
RT8251 |
||
|
GE=YM |
YMDNN : Date Code |
|
YMDNN : Date Code |
|
|
|
GSPYMDNN |
|||
|
DNN |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Typical Application Circuit
|
|
|
VIN |
|
|
|
|
|
|
|
|
|
|
|
1, 2, 3, |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
15, 16 |
|
4.75V to 24V |
|
|
|
|
|
|
|
|
|
|
CIN |
|
|||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Chip Enable |
|
|
|
|
|
|
|
|
|
|
10µF x 2 |
7 |
|||
|
|
|
|
|
|
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
|
|
8 |
||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
CSS |
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
|
|
10nF |
4, |
|||
|
|
|
|
|
|
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
|
|
Exposed Pad (17) |
||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
VIN |
BOOT |
9 |
|
CBOOT |
L |
|
RT8251 |
|
|
|
|||
10 to 14 |
100nF |
4.7µH |
VOUT |
|||
EN |
SW |
D |
|
|||
|
|
|
R1 |
3.3V/5A |
||
|
|
|
|
B540C |
|
|
SS |
|
5 |
|
30.9k |
COUT |
|
FB |
|
|
||||
|
|
|
|
|||
|
|
CC |
RC |
R2 |
22µF x 2 |
|
|
|
|
||||
GND |
COMP 6 |
2.2nF |
22k |
10k |
|
|
|
|
|
|
|||
|
|
|
CP |
|
|
|
|
|
|
(Open) |
|
|
|
|
Figure 1. Typical Application Circuit for WQFN-16L 3x3 |
||||||
VIN |
2 |
VIN |
BOOT 1 |
CBOOT |
|
||
4.75V to 24V |
CIN |
|
|
|
|
||
|
10µF x 2 |
|
RT8251 |
3 |
100nF |
L |
VOUT |
Chip Enable |
|
|
SW |
|
|
||
7 |
EN |
|
D |
4.7µH |
3.3V/5A |
||
|
|
|
R1 |
||||
|
8 |
|
|
|
B540C |
30.9k |
|
CSS |
SS |
FB 5 |
|
|
COUT |
||
4, |
|
|
|
CC |
RC |
22µF x 2 |
|
10nF |
Exposed Pad(9) |
|
|
|
R2 |
||
|
GND |
COMP 6 |
2.2nF |
22k |
10k |
||
|
|
|
|
|
|||
|
|
|
|
|
CP |
|
|
|
|
|
|
|
NC |
|
|
Figure 2. Typical Application Circuit for SOP-8 (Exposed Pad)
Table 1. Recommended Component Selection
|
VOUT (V) |
R1 (kΩ) |
R2 (kΩ) |
RC (kΩ) |
CC (nF) |
L1 (μH) |
|
COUT (μF) |
|
|
|
15 |
182 |
10 |
51 |
1 |
22 |
|
44 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
10 |
115 |
10 |
43 |
1.2 |
10 |
|
44 |
|
|
|
8 |
91 |
10 |
39 |
1.5 |
10 |
|
44 |
|
|
|
5 |
52.3 |
10 |
30 |
1.5 |
6.8 |
|
44 |
|
|
|
3.3 |
30.9 |
10 |
22 |
2.2 |
4.7 |
|
44 |
|
|
|
2.5 |
21.5 |
10 |
16 |
2.2 |
4.7 |
|
44 |
|
|
|
1.8 |
12.4 |
10 |
13 |
2.2 |
2.2 |
|
44 |
|
|
|
1.2 |
4.99 |
10 |
13 |
2.2 |
2.2 |
|
44 |
|
|
|
|
|
|
|
|
|
|
|
|
|
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
|
is a registered trademark of Richtek Technology Corporation. |
||||||||
www.richtek.com |
|
|
|
|
|
DS8251-04 February 2013 |
||||
2
RT8251
Functional Pin Description
Pin No. |
|
|
||
WQFN-16L 3x3 |
SOP-8 |
Pin Name |
Pin Function |
|
(Exposed Pad) |
|
|
||
|
|
|
||
|
|
|
Power Input. VIN supplies the power to the IC, as well as the |
|
|
|
|
step-down converter switches. Connect VIN with a 4.75V to 24V |
|
1, 2, 3, 15, 16 |
2 |
VIN |
power source. Connect VIN to GND with a capacitor that the |
|
|
|
|
capacitance is large enough to eliminate noise on the input to the |
|
|
|
|
IC. |
|
|
|
|
Ground. This pin is the voltage reference for the regulated output |
|
|
|
|
voltage. For this reason, care must be taken in its layout. This |
|
4, |
4, |
GND |
node should be placed outside of the D1 to CIN ground path to |
|
17 (Exposed Pad) |
9 (Exposed Pad) |
prevent switching current spikes from inducing voltage noise into |
||
|
|
|
the part. The exposed pad must be soldered to a large PCB and |
|
|
|
|
connected to GND for maximum power dissipation. |
|
5 |
5 |
FB |
Feedback Input. An external resistor divider from the output to |
|
GND, tapped to the FB pin, sets the output voltage. |
||||
|
|
|
||
|
|
|
Compensation Node. This node is the output of the |
|
6 |
6 |
COMP |
transconductance error amplifier and the input to the current |
|
comparator. Frequency compensation is done at this node by |
||||
|
|
|
||
|
|
|
connecting a series R-C to ground. |
|
|
|
|
Enable Input. EN is a digital input that turns the regulator on or |
|
7 |
7 |
EN |
off. Drive EN higher than 1.4V to turn on the regulator, lower |
|
than 0.4V to turn it off. For automatic startup, leave EN |
||||
|
|
|
||
|
|
|
unconnected. |
|
|
|
|
Soft-Start Control Input. SS controls the soft start period. |
|
8 |
8 |
SS |
Connect a capacitor ( 10nF) from SS to GND to set the |
|
soft-start period. A 10nF capacitor sets the Soft-Start period to |
||||
|
|
|
||
|
|
|
1ms. |
|
|
|
|
Bootstrap. This capacitor CBOOT is needed to drive the power |
|
|
|
|
switch’s gate above the supply voltage. It is connected between |
|
9 |
1 |
BOOT |
the SW and BS pins to form a floating supply across the power |
|
switch driver. The voltage across CBOOT is about 5V and is |
||||
|
|
|
||
|
|
|
supplied by the internal +5V supply when the SW pin voltage is |
|
|
|
|
low. |
|
|
|
|
Power Switching Output. SW is the switching node that supplies |
|
10, 11, 12, 13, |
3 |
SW |
power to the output. Connect the output LC filter from SW to the |
|
14 |
output load. Note that a capacitor is required from SW to BOOT |
|||
|
|
|||
|
|
|
to power the high-side switch. |
|
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8251-04 February 2013 |
www.richtek.com |
3
RT8251
Function Block Diagram
VIN |
|
|
|
|
|
Current Sense |
|
|
VCC |
|
|
|
|
|
|||
Internal |
|
Oscillator |
Slope Comp |
Amplifier |
|
|||
|
|
|
|
|||||
1µA |
|
Regulator |
570kHz |
|
|
+ |
VA |
|
|
VA VCC |
|
|
|
|
- |
|
|
10k |
|
|
Foldback |
|
|
|
BOOT |
|
|
- |
|
Control |
|
|
|
||
EN |
|
|
|
|
|
|||
|
1.1V |
+ |
0.4V |
+ |
|
|
|
SW |
|
|
Shutdown |
|
Logic |
||||
3V |
|
|
- |
+ |
||||
Comparator |
|
|
||||||
|
|
UV |
|
|
|
|||
|
VCC |
|
|
- |
|
|
|
|
|
|
Comparator |
|
|
GND |
|||
|
|
10µA |
|
|
Current |
|
|
|
|
|
0.8V |
+ |
Comparator |
|
|
|
|
SS |
|
|
|
|
|
|
||
|
|
|
+EA |
|
|
|
|
|
|
|
|
|
- |
|
|
|
|
|
|
|
Gm = 820µA/V |
|
|
|
|
|
|
|
|
FB |
COMP |
|
|
|
|
Absolute Maximum Ratings (Note 1)
z Supply Voltage, VIN ------------------------------------------------------------------------------------------ |
−0.3V to 26V |
z Switching Voltage, VSW ------------------------------------------------------------------------------------- |
−0.3V to (VIN + 0.3V) |
z BOOT Voltage, VBOOT --------------------------------------------------------------------------------------- |
(VSW − 0.3V) to (VSW + 6V) |
z All Other Pins ------------------------------------------------------------------------------------------------- |
−0.3V to 6V |
z Power Dissipation, PD @ TA = 25°C |
|
WQFN-16L 3x3 ----------------------------------------------------------------------------------------------- |
1.471W |
SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------- |
1.333W |
z Package Thermal Resistance (Note 2) |
|
WQFN-16L 3x3, θJA ------------------------------------------------------------------------------------------ |
68°C/W |
WQFN-16L 3x3, θJC ----------------------------------------------------------------------------------------- |
7.5°C/W |
SOP-8 (Exposed pad), θJA --------------------------------------------------------------------------------- |
75°C/W |
SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------- |
15°C/W |
z Junction Temperature ---------------------------------------------------------------------------------------- |
150°C |
z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------ |
260°C |
z Storage Temperature Range ------------------------------------------------------------------------------- |
−65°C to 150°C |
z ESD Susceptibility (Note 3) |
|
HBM (Human Body Model) --------------------------------------------------------------------------------- |
2kV |
Recommended Operating Conditions |
(Note 4) |
z Supply Voltage, VIN ------------------------------------------------------------------------------------------ |
4.75V to 24V |
z Enable Voltage, VEN ----------------------------------------------------------------------------------------- |
0V to 5.5V |
z Junction Temperature Range ------------------------------------------------------------------------------- |
−40°C to 125°C |
z Ambient Temperature Range ------------------------------------------------------------------------------- |
−40°C to 85°C |
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8251-04 February 2013 |
4
RT8251
Electrical Characteristics
(VIN = 12V, TA = 25°C unless otherwise specified)
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
|
|
|
|
|
|
|
|
|
Feedback Reference Voltage |
VFB |
4.75V VIN 24V |
0.784 |
0.8 |
0.816 |
V |
|
High-Side Switch-On Resistance |
RDS(ON)1 |
|
-- |
70 |
-- |
mΩ |
|
Low-Side Switch-On Resistance |
RDS(ON)2 |
|
-- |
15 |
-- |
Ω |
|
High-Side Switch Leakage |
|
VEN = 0V, VSW = 0V |
-- |
-- |
10 |
μA |
|
Current Limit |
|
ILIM |
Duty = 85%; VBOOT−SW = 4.8V |
-- |
6.8 |
-- |
A |
Current Sense Transconductance |
GCS |
Output Current to VCOMP |
-- |
4.6 |
-- |
A/V |
|
Error Amplifier Tansconductance |
gm |
IC = ±10μA |
-- |
920 |
-- |
μA/V |
|
Oscillator Frequency |
|
fSW |
|
420 |
570 |
720 |
kHz |
Short Circuit Oscillation Frequency |
|
VFB = 0V |
-- |
185 |
-- |
kHz |
|
Maximum Duty Cycle |
|
DMAX |
VFB = 0.7V |
-- |
85 |
-- |
% |
Minimum On-Time |
|
tON |
|
-- |
100 |
-- |
ns |
UVLO Threshold Rising |
|
|
-- |
4.1 |
-- |
V |
|
UVLO Threshold Hysteresis |
|
|
-- |
200 |
-- |
mV |
|
EN Input Voltage |
Logic Low |
VIL |
|
-- |
-- |
0.4 |
V |
Logic High |
VIH |
|
1.4 |
-- |
5.5 |
||
|
|
|
|||||
Enable Pull Up Current |
|
VEN = 0V |
-- |
1 |
-- |
μA |
|
Shutdown Current |
|
ISHDN |
VEN = 0V |
-- |
25 |
-- |
μA |
Quiescent Current |
|
IQ |
VEN = 2V, VFB = 1V |
-- |
0.8 |
1 |
mA |
Soft-Start Current |
|
ISS |
VSS = 0V |
-- |
10 |
-- |
μA |
Soft-Start Period |
|
|
CSS = 10nF |
-- |
1 |
-- |
ms |
Thermal Shutdown |
|
TSD |
|
-- |
150 |
-- |
°C |
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8251-04 February 2013 |
www.richtek.com |
5
RT8251
Typical Operating Characteristics
Efficiency vs. Load Current
|
100 |
|
|
|
|
|
|
|
|
|
|
|
90 |
|
|
|
|
|
|
|
VIN = 12V |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
80 |
|
|
|
|
|
|
|
VIN = 24V |
|
|
(%) |
70 |
|
|
|
|
|
|
|
|
|
|
60 |
|
|
|
|
|
|
|
|
|
|
|
Efficiency |
|
|
|
|
|
|
|
|
|
|
|
50 |
|
|
|
|
|
|
|
|
|
|
|
40 |
|
|
|
|
|
|
|
|
|
|
|
30 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
20 |
|
|
|
|
|
|
|
|
|
|
|
10 |
|
|
|
|
|
|
|
VOUT = 3.3V |
|
|
|
0 |
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
0 |
0.5 |
1 |
1.5 |
2 |
2.5 |
3 |
3.5 |
4 |
4.5 |
5 |
Efficiency vs. Load Current
|
100 |
|
|
|
|
|
|
|
VIN = 12V |
||
|
90 |
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
VIN = 24V |
|
||
|
80 |
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
Efficiency(%) |
70 |
|
|
|
|
|
|
|
|
|
|
60 |
|
|
|
|
|
|
|
|
|
|
|
50 |
|
|
|
|
|
|
|
|
|
|
|
40 |
|
|
|
|
|
|
|
|
|
|
|
30 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
20 |
|
|
|
|
|
|
|
|
|
|
|
10 |
|
|
|
|
|
|
|
VOUT = 5V |
|
|
|
0 |
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
0 |
0.5 |
1 |
1.5 |
2 |
2.5 |
3 |
3.5 |
4 |
4.5 |
5 |
Load Current (A) |
Load Current (A) |
Output Voltag Deviation vs. Load Current |
Output Voltage Deviation vs. Input Voltage |
|
2 |
VIN = 24V |
|
|
|
|
|
2 |
IOUT = 5A |
|
|
|
|
|
|
|
(%)1 |
|
|
|
|
|
(%)1 |
|
|
|
|
|
|
|
|
||
1.5 |
VIN = 12V |
|
|
|
|
1.5 |
IOUT = 3A |
|
|
|
|
|
|
|
||
|
VIN = 5V |
|
|
|
|
|
IOUT = 0A |
|
|
|
|
|
|
|
||
Deviation |
1 |
|
|
|
|
Deviation |
1 |
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
||||
0.5 |
|
|
|
|
|
0.5 |
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
Voltage |
0 |
|
|
|
|
|
Voltage |
0 |
|
|
|
|
|
|
|
|
-0.5 |
|
|
|
|
|
-0.5 |
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
Output |
-1 |
|
|
|
|
|
Output |
-1 |
|
|
|
|
|
|
|
|
-1.5 |
|
|
|
VOUT = 3.3V |
|
-1.5 |
|
|
|
|
|
VOUT = 3.3V |
|
|||
|
|
|
|
|
|
|
|
|
|
|
|
|||||
|
-2 |
|
|
|
|
|
-2 |
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
|
0.001 |
0.01 |
0.1 |
1 |
10 |
|
4 |
6.5 |
9 |
11.5 |
14 |
16.5 |
19 |
21.5 |
24 |
|
Load Current (A) |
Input Voltage (V) |
|
Quiescent Current vs. Temperature
|
1.2 |
|
|
|
|
|
|
|
(mA) |
1 |
|
|
|
|
|
|
|
0.8 |
|
|
|
|
|
|
|
|
Current |
|
|
|
|
|
|
|
|
0.6 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Quiescent |
0.4 |
|
|
|
|
|
|
|
0.2 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0 |
|
|
|
|
|
VIN = 12V |
|
|
|
|
|
|
|
|
|
|
|
-50 |
-25 |
0 |
25 |
50 |
75 |
100 |
125 |
Temperature (°C)
Reference Voltage vs. Temperature
|
0.816 |
|
|
|
|
|
|
|
|
0.811 |
|
|
|
|
|
|
|
(V) |
0.806 |
|
|
|
|
|
|
|
Voltage |
|
|
|
|
|
|
|
|
0.801 |
|
|
|
|
|
|
|
|
Reference |
0.796 |
|
|
|
|
|
|
|
0.791 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0.786 |
|
|
|
|
|
VIN = 12V |
|
|
|
|
|
|
|
|
|
|
|
-50 |
-25 |
0 |
25 |
50 |
75 |
100 |
125 |
Temperature (°C)
Copyright ©2013 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8251-04 February 2013 |
6
Loading...