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PDF RT8110 Data sheet ( Hoja de datos )
| Número de pieza | RT8110 | |
| Descripción | Compact Synchronous Buck DC/DC PWM Controller | |
| Fabricantes | RICHTEK | |
| Logotipo |  |
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RT8110
Compact Synchronous Buck DC/DC PWM Controller
General Description
The RT8110 is a compact fixed-frequency PWM controller
with integrated MOSFET drivers for single-phase
synchronous buck converter. This part features wide input
voltage range operation and tiny package. An internal pre-
regulator drives an external BJT to provide regulated output
voltage from the input voltage to support VCC. Therefore,
the controller can operate with wide input voltage range.
The RT8110 utilizes voltage-mode control with internal
compensation to simplify the converter design. An internal
0.8V reference voltage allows low output voltage
application. The switching frequency is fixed at 400kHz
to reduce the external passive component size to save
board space. Low-side MOSFET RDS(ON) is used for
inductor current sensing. The RT8110 provides under
voltage protection, current limit, over current protection
and over temperature protection.
Ordering Information
RT8110
Package Type
J8 : TSOT-23-8
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial Standard)
Note :
Richtek Pb-free and Green 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.
Features
z 8V to 23V Wide Range Operation
z 0.8V Internal Reference
z Internal Soft Start
z High DC Gain Voltage Mode PWM Control
z Fixed 400kHz Switching Frequency
z Fast Transient Response
z Fully Dynamic 0 to 80% Duty Cycle
z Over Current Protection
z Under Voltage Protection
z Over Temperature Protection
z Tiny Package TSOT-23-8
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z Set-top Box Power Supplies
z PC Subsystem Power Supplies
z Cable Modems, DSL Modems
z DSP and Core Communication Processor Power
Supplies
z Memory Power Supplies
z Personal Computer Peripherals
z Industrial Power Supplies
z Low Voltage Distributed Power Supplies
Pin Configurations
(TOP VIEW)
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
87 6 5
2 34
TSOT-23-8
DS8110-00 May 2009
www.richtek.com
1
Free Datasheet http://www.datasheet4u.com/
1 page  
RT8110
Parameter
Symbol
Test Conditions
Min Typ Max Units
Upper Drive Sink
Lower Drive Source
Lower Drive Sink
Upper Drive Source
Upper Drive Sink
Lower Drive Source
Lower Drive Sink
Protection
Over Current Threshold
Maximum Duty Cycle
RUS INK
VUGATE −PHASE = 1V
VBOOT − PHASE = 5V
RLSOURCE VCC − VLGATE = 1V
RLSINK
VLGATE = 1V
IUSOURCE VBOOT −VUGATE = 5V
IUS INK
VUGATE −PHASE = 5V
IUSOURCE VVCC −VLGATE = 5V
IUS INK
VLGATE −GND = 5V
VOC Sense Phase Pin Voltage
-- 2 3
-- 4 6
-- 2 4
-- 0.72 --
-- 0.82 --
-- 0.65 --
-- 1.18 --
Ω
Ω
Ω
A
A
A
A
−230 −200 −170
-- 80 --
mV
%
UVP Threshold
Soft Start
FB Falling
-- 0.5 0.6 V
Soft-Start Interval
TSS
1 3 6 ms
Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These
are for stress ratings. 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
for extended periods may remain possibility to affect device reliability.
Note 2. Devices are ESD sensitive. Handling precaution recommended.
Note 3. The device is not guaranteed to function outside its operating conditions.
Note 4. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test
board of JEDEC 51-3 thermal measurement standard.
Note 5. Guarantee by design.
DS8110-00 May 2009
www.richtek.com
5
Free Datasheet http://www.datasheet4u.com/
5 Page 
RT8110
regulate the output voltage according to the ratio of the
voltage divider resistors R1 and R2.
VOUT
Transconductance
Error Amplifier
-
GM
+
+
VREF
R1
FB
R2
Figure 8. Voltage Divider Resistors
If R1 is given and the output voltage is specified, then R2
can be determined using the following equation :
R2
=
R1× ⎛⎜⎝
VREF
VOUT − VREF
⎞⎟⎠
Feedback Compensation and Output Capacitor
Selection
The RT8110 is a voltage-mode PWM controller with fixed
switching frequency, it uses operational transconductance
amplifier (OTA) with internal compensation network to
eliminate external compensation components.
The compensation network is used to shape the gain curve
to obtain accurate dc regulation, fast load transient
response and maintain stability. Figure 9 shows the Bode
plot of the modulation gain, compensation gain and the
close loop gain. A stable control loop has a close gain
curve with a -20dB/decade slope at the crossover
frequency and the phase margin is greater than 45°.
Gain (dB)
FLC FESR
FC
Compensation Gain
0
FZ1 FP1
FZ2
Freq.(Log)
Close Loop Gain
Modulation Gain
FP2
Figure 9. Bode Plot of Loop Gain.
Figure 10 illustrates the simplified synchronous buck
converter using OTA with internal compensation. The
feedback loop consists of Zin (R1, R2 and C1), OTA and
the internal compensation network ZFB (RS, CS, CP). The
value of internal compensation component is: RS ≈50k,
CS ≈4nF, CP ≈10pF.
Q1
+
VIN
Output Inductor
L DCR
Output
Q2 Capacitor
ESR
COUT
RLOAD
Optional
PWM Generator
& MOSFET
Driver
CP≈10pF
Transconductance
Error Amplifier
-
GM
+
RS≈50k
+
CS≈4nF VREF
C3
R1
R3
R2
Figure 10. Simplified Diagram for Synchronous Buck
Converter with Internal Compensation Network
Referring to Figure 9, the location of pole and zero of the
LC filter and the compensation network can be determined
using the following equations. The inductor and the output
capacitor create a double pole at FLC :
FLC = 2π ×
1
L × COUT
The equivalent series resistance (ESR) of the output
capacitor creates a zero at FESR :
FESR
=
1
2π ×ESR × COUT
The internal compensation network introduces a zero at
FZ1 :
FZ1 =
1
2π ×RS × CS
The internal compensation network also introduces a pole
at FP2 :
FP2
=
1
2π
× RS
× ⎛⎜⎝
CS
CS
× CP
+ CP
⎞⎟⎠
DS8110-00 May 2009
www.richtek.com
11
Free
Datas
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| PDF Descargar | [ Datasheet RT8110.PDF ] | |
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