RT4812 - Richtek

RT4812
High Efficiency Boost Converter
General Description
Features
The RT4812 allows systems to take advantage of new
battery chemistries that can supply significant energy
when the battery voltage is lower than the required
voltage for system power ICs. By combining built-in

power transistors, synchronous rectification, and low
supply current; this IC provides a compact solution for
systems using advanced Li-Ion battery chemistries.

The RT4812 is a boost regulator designed to provide a
minimum output voltage from a single-cell Li-Ion battery,
even when the battery voltage is below system
minimum. In boost mode, output voltage regulation is
guaranteed to a maximum load current of 2A.
Quiescent current in Shutdown Mode is less than 1A,
which maximizes battery life.










CMCOT Topology and Small Output Ripple
when VIN close VOUT Voltage
Operates from a Single Li-ion Cell : 1.8V to 5.5V
Adjustable Output Voltage : 1.8V to 5.5V
PSM Operation
Up to 96% Efficiency
Boost Current Limit
Input/Output Over Voltage Protection
Pin Adjustable Current Limit Threshold
(2 levels)
Internal Compensation
Output Discharge
Output Short Protection
True Load Disconnect
Applications
Ordering Information

RT4812

Single-Cell Li-Ion, LiFePO4 Smart-Phones
Portable Equipment
Package Type
J8F : TSOT-23-8 (FC)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Marking Information
0L=DNN
Note :
0L= : Product Code
DNN : Date Code
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.
Simplified Application Circuit
RT4812
L1
SW
VIN
VOUT
VOUT
C1
R1
VIN
CFF
C3
FB
C2
R2
EN
H/L
ILIM
GND
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June 2015
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RT4812
Pin Configurations
EN
SW
GND
8
7
6
5
2
3
4
FB
VOUT
PGND
VIN
ILIM
(TOP VIEW)
TSOT-23-8 (FC)
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
VIN
Power Input. Input capacitor CIN must be placed as close to IC as possible.
2
FB
Voltage Feedback.
3
VOUT
Boost Converter Output.
4
PGND
Power Ground.
5
GND
Analog Ground.
6
SW
Switching Node.
7
EN
Enable Input (1 enabled, 0 disabled), must not be left open.
8
ILIM
Current Limit Control Pin. (H/L)
Functional Block Diagram
VOUT
VIN
SW Control
ILIM
OCP
Gate
DRV
EN
Digital
CTRL
PWM
CTRL
SW
AMP
-
FB
+
OSC
OTP
PGND
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UVLO
VREF
GND
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RT4812
Operation
RT4812
combined
built-in
power
transistors,
Startup and Shutdown State
synchronous rectification, and low supply current, it
provides a compact solution for system using advanced
Li-Ion battery chemistries.
When VIN is rising and through the LIN state, it will
enter the Startup state. If EN is pulled low, any
function is turned-off in shutdown mode.
In boost mode, output voltage regulation is guaranteed
to a maximum load current of 2A. Quiescent current in
Shutdown mode is less than 1A, which maximizes
battery life.
Soft-Start State
Mode
Depiction
Condition
LIN 1
Linear startup 1
VIN > VOUT
LIN 2
Linear startup 2
VIN > VOUT
Soft-Start
Boost soft-start
VOUT < VOUT(MIN)
Boost
Boost mode
VOUT = VOUT(MIN)
LIN
LIN State
When VIN is rising, it enters the LIN State. There are
two parts for the LIN state. It provides maximum
current for 1A to charge the COUT in LIN1, and the
other one is for 2A in LIN2. By the way, the EN is
pulled high and VIN > UVLO.
As the figure shown, if the timeout is over the
specification, it will enter the Fault mode.
Timeout > 512μs
Timeout
< 1024μs
Boost
mode
Fault State
As the Figure 1 shown, it will enter to the Fault state
as below,

The timeout of LIN2 is over the 1024s.
It will be the high impedance between the input and
output when the fault is triggered. A restart will be
start after 1ms.
OCP
The converter senses the current signal when the
high-side P-MOSFET turns on. As a result, the OCP
is cycle by-cycle current limitation. If the OCP occurs,
the converter holds off the next on pulse until inductor
current drops below the OCP limit.
The converter has an over-temperature protection.
When the junction temperature is higher than the
LIN 1
Soft-Start
output voltage is rising with the internal reference
voltage.
OTP
EN = 1,
Vin > UVLO
Timeout < 512μs
It starts to switch in Soft-start state. After the LIN state,
LIN 2
thermal shutdown rising threshold, the system will be
latched and the output voltage will no longer be
regulated until the junction temperature drops under
the falling threshold.
Timeout > 1024μs
Fault
State
Figure 1. RT4812 State Chart
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RT4812
Absolute Maximum Ratings
(Note 1)

VIN, VINA to GND -------------------------------------------------------------------------------------------------- 0.2V to 6V

VOUT to GND-------------------------------------------------------------------------------------------------------- 6.2V

Power Dissipation, PD @ TA = 25C

TSOT-23-8 (FC) ----------------------------------------------------------------------------------------------------- 1.78W

Package Thermal Resistance
(Note 2)
TSOT-23-8 (FC), JA ----------------------------------------------------------------------------------------------- 56C/W
TSOT-23-8 (FC), JC ----------------------------------------------------------------------------------------------- 28C/W

Lead Temperature (Soldering, 10sec.) ------------------------------------------------------------------------- 260C

Junction Temperature -------------------------------------------------------------------------------------------- 65C to 150C

Storage Temperature Range ------------------------------------------------------------------------------------- 65C to 150C

ESD Susceptibility
(Note 3)
HBM (Human Body Model) -------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ---------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
(Note 4)

Input Voltage Range ---------------------------------------------------------------------------------------------- 1.8V to 5.5V

Output Voltage Range --------------------------------------------------------------------------------------------- 1.8V to 5.5V

Junction Temperature (TJ) Range------------------------------------------------------------------------------- 40C to 125C

Ambient Temperature (TJ) Range ------------------------------------------------------------------------------- 40C to 85C
Electrical Characteristics
(VBAT = 3.6V, TA = 25C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Supply Voltage
VIN
VIN  VOUT 0.2V
1.8
--
5.5
V
Output Voltage
VOUT
VIN  VOUT 0.2V
1.8
--
5.5
V
Under Voltage Lockout
Rising Threshold
UVLO_RISE
1.6
1.7
1.8
V
Under Voltage Lockout
Falling Threshold
UVLO_Falling
1.5
1.6
1.7
V
FB Voltage (ADJ)
VFB
Force PWM
0.495
0.5
0.505
V
Regulated DC VOUT Voltage
VOUT
1.8  VIN  VOUT  0.2V
IOUT = 0mA (PSM)
2
--
4
%
Shutdown Current
ISHDN
EN = 0V
--
0.1
2
A
Close loop, no load
FB = 3V, non-switching current
--
40
--
A
--
1
--
A
--
0.5
--
MHz
ILIM = L
3.3
--
--
ILIM = H
5.3
--
--
VIN = 5V
--
40
--
Quiescent Current
Pre-charge Current
Ipre
Switching Frequency
f SW
Valley Current Limit
ILIM
High Side Switch Ron
VOUT  VIN > 1V
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RT4812
Parameter
Symbol
Low Side Switch Ron
Test Conditions
Min
Typ
Max
Unit
VIN = 5V
--
20
--
m
FB Pin Input Leakage
IFB
ADJ mode
1
--
1
A
Leakage of SW
ISW
All switch off
--
--
5
A
Line Regulation
VOUT, LINE
PVIN = 2.7V to 4.5V, VOUT = 5V,
IOUT = 1500mA
2
--
2
%
Load Regulation
VOUT, LOAD
CCM, IOUT  2A, PVIN = 3.6V,
VOUT = 5V
1.5
--
1.5
%
Output Over Voltage
Protection
VOVP
5.8
6
6.2
V
EN Input Low Voltage
VIL
--
--
0.4
V
EN Input High Voltage
VIH
1.2
--
--
V
--
0.1
1
A
EN
Thermal Shutdown
TSD
--
160
C
Thermal Shutdown
Hysteresis
TSD
--
30
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. JA is measured at TA = 25C on a two-layer Richtek Evaluation Board.
Note 3. Devices are ESD sensitive. Handling precaution recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
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RT4812
Typical Application Circuit
RT4812
L1
VIN
6
SW
VOUT
C1
22μF
1
VIN
FB
C2
1μF
3
2
VOUT
R1
45.3k
CFF
150pF to
220pF
C3
47μF x 2
CFF
10pF
C3
47μF x 2
R2
4.99k
7 EN
8 ILIM
GND
5
PGND
4
Figure 2
RT4812
L1
VIN
6
SW
VOUT
C1
22μF
1
VIN
FB
C2
1μF
3
2
VOUT
R1
909k
R2
100k
7 EN
8 ILIM
GND
5
PGND
4
Figure 3
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RT4812
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
80
VIN = 4.2V
80
VIN = 2.5V
70
VIN = 3.6V
70
VIN = 1.8V
60
VIN = 2.5V
Efficiency (%)
Efficiency (%)
90
VIN = 1.8V
50
40
30
20
COUT = 47μF x 2
400
800
40
30
VOUT = 3.6V, L = 1.5μH (TDK SPM6530)
10
COUT = 47μF x 2
0
0
0
50
20
VOUT = 5V, L = 1.5μH (TDK SPM6530)
10
60
1200
1600
0
2000
400
Efficiency vs. Outout Current
1200
100
90
90
80
VIN = 4.2V
80
VIN = 2.5V
70
VIN = 3.7V
70
VIN = 1.8V
60
VIN = 3.3V
VIN = 2.5V
50
VIN = 1.8V
40
30
20
VOUT = 5V, L = 1.5μH (TDK SPM6530), R1 = 909k,
10
1600
2000
Efficiency vs. Output Current
100
Efficiency (%)
Efficiency (%)
800
Output Current (mA)
Output Current (mA)
60
50
40
30
20
VOUT = 3.6V, L = 1.5μH (TDK SPM6530), R1 = 909k,
10
R2 = 100k, C FF = 10pF, C OUT = 47μF x 2
0
R2 = 100k, C FF = 10pF, C OUT = 47μF x 2
0
0
400
800
1200
1600
2000
2400
0
400
800
1200
1600
2000
Outout Current (mA)
Output Current (mA)
Output Voltage Ripple
Output Voltage Ripple
2400
VBAT = 2.5V, VOUT = 5V, IOUT = 1000mA
LX
(2V/Div)
LX
(2V/Div)
VOUT_ac
(20mV/Div)
VOUT_ac
(50mV/Div)
VBAT = 2.5V, VOUT = 5V, IOUT = 0mA
L = 1.5H, COUT = 47F x 2
Time (10s/Div)
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L = 1.5H, COUT = 47F x 2
Time (1s/Div)
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RT4812
Output Voltage Ripple
Output Voltage Ripple
LX
(2V/Div)
LX
(2V/Div)
VOUT_ac
(20mV/Div)
VOUT_ac
(50mV/Div)
VBAT = 3.6V, VOUT = 5V, IOUT = 1000mA
L = 1.5H, COUT = 47F x 2
VBAT = 3.6V, VOUT = 5V, IOUT = 0mA
L = 1.5H, COUT = 47F x 2
Time (10s/Div)
Time (1s/Div)
Output Voltage Ripple
Output Voltage Ripple
LX
(2V/Div)
LX
(2V/Div)
VOUT_ac
(20mV/Div)
VOUT_ac
(50mV/Div)
VBAT = 4.2V, VOUT = 5V, IOUT = 0mA
L = 1.5H, COUT = 47F x 2
Time (10s/Div)
Time (1s/Div)
Load Transient Response
Load Transient Response
IOUT
(1A/Div)
IOUT
(1A/Div)
VOUT_ac
(200mV/Div)
VBAT = 4.2V, VOUT = 5V, IOUT = 1000mA,
L = 1.5H, COUT = 47F x 2
VBAT = 3.7V, VOUT = 5V,
IOUT = 1000mA to 2000mA
L = 1.5H, COUT = 47F x 2
VBAT = 2.5V, VOUT = 5V,
IOUT = 1000mA to 2000mA
L = 1.5H, COUT = 47F x 2
VOUT_ac
(200mV/Div)
Time (500s/Div)
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RT4812
Load Transient Response
IOUT
(1A/Div)
VBAT = 4.2V, VOUT = 5V,
IOUT = 1000mA to 2000mA
L = 1.5H, COUT = 47F x 2
VOUT_ac
(200mV/Diiv)
Time (500s/Div)
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RT4812
Application Information
Enable
Power Save Mode
The device can be enabled or disabled by the EN pin.
When the EN pin is higher than the threshold of
logic-high, the device starts operating with soft-start.
Once the EN pin is set at low, the device will be shut
down. In shutdown mode, the converter stops
PSM is the way to improve efficiency at light load.
switching, internal control circuitry is turned off, and
the load is disconnected from the input. This also
means that the output voltage can drop below the
input voltage during shutdown.
When the output voltage is lower than a set threshold
voltage, the converter will operate in PSM.
It raises the output voltage with several pulses until
the loop exits PSM.
Under-Voltage Lockout
The under-voltage lockout circuit prevents the device
from operating incorrectly at low input voltages. It
prevents the converter from turning on the power
switches under undefined conditions and prevents the
Soft-Start State
After the successful completion of the LIN state (VOUT
≥ VIN = 300mV), the regulator begins switching with
boost valley-current limited value 1000mA.
battery from deep discharge. VIN voltage must be
greater than 1.7V to enable the converter. During
During Soft-Start state, VOUT is ramped up by Boost
internal loop. If VOUT fails to reach target value during
the Soft-Start period for more than 2ms, a fault
condition is declared.
operation, if VIN voltage drops below 1.6V, the
converter is disabled until the supply exceeds the
UVLO rising threshold. The RT4812 automatically
restarts if the input voltage recovers to the input
voltage UVLO high level.
Output Voltage Setting
Thermal Shutdown
The output voltage is adjustable by an external
The device has a built-in temperature sensor which
resistive divider. The resistive divider must be
connected between VOUT, FB and GND. When the
output voltage is regulated properly, the typical value
of the voltage at the FB pin is 500mV. Output voltage
can be calculated by equation as below :
monitors the internal junction temperature. If the
temperature exceeds the threshold, the device stops
V

R1  R2   OUT  1
 VFB

operating. As soon as the IC temperature has
decreased below the threshold with a hysteresis, it
starts operating again. The built-in hysteresis is
designed to avoid unstable operation at IC
temperatures near the over temperature threshold.
Inductor Selection
The recommended nominal inductance value is
1.5H
It is recommended to use inductor with dc saturation
current ≥ 5000mA
Table 1. List of Inductors
Manufacturer
Series
Dimensions (in mm)
Saturation Current (mA)
TDK
SPM6530T
7.1 x 6.5 x 3.0
11500
Taiyo Yuden
NRS5040T
5.15 x 5.15 x 4.2
6400
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RT4812
Input Capacitor Selection
Output Discharge Function
At least a 22F input capacitor is recommended to
With the EN pin set to low, the VOUT pin is internally
improve transient behavior of the regulator and EMI
behavior of the total power supply circuit for LX. And
at least a 1F ceramic capacitor placed as close as
possible to the VIN and GND pins of the IC is
recommended.
connected to GND
N-MOSFET switch.
Output Capacitor Selection
Current Limit
At least 47F x 2 capacitors is recommended to
improve VOUT ripple.
RT4812 employs a valley-current limit detection
scheme to sense inductor current during the off-time.
When the loading current is increased such that the
loading is above the valley current limit threshold, the
off-time is increased until the current is decreased to
valley-current threshold. Next on-time begins after
current is decreased to valley-current threshold.
On-time is decided by (VOUT VIN) / VOUT ratio. The
output voltage decreases when further loading
Output voltage ripple is inversely proportional to
COUT.
Output capacitor is selected according to output ripple
which is calculated as :
VRIPPLE(P P)  tON 
ILOAD
COUT
and
tON  tSW  D  tSW
by
an
internal
discharge
This feature prevents residual charge voltages on
capacitor connected to VOUT pins, which may impact
proper power up of the system.
current increase. The current limit function is
implemented by the scheme, refer to Figure 4.

V 
  1  IN 
VOUT 

therefore :

V 
ILOAD
COUT  tSW   1  IN  
VOUT  VRIPPLE(P P)

and
tSW 
1
fSW
The maximum VRIPPLE occurs when VIN is at
minimum and ILOAD is at maximum.
IIN (DC)
Valley Current Limit
f
Inductor Current
IL
IL =
IIN (DC)
VIN D

L
f
Figure 4. Inductor Currents In Current Limit Operation
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RT4812
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
Maximum Power Dissipation (W)1
2.0
dissipation depends on the thermal resistance of the
IC package, PCB layout, rate of surrounding airflow,
and difference between junction and ambient
temperature. The maximum power dissipation can be
calculated by the following formula :
PD(MAX) = (TJ(MAX)  TA) / JA
where TJ(MAX) is the maximum junction temperature,
TA is the ambient temperature, and JA is the junction
to ambient thermal resistance.
Two-Layer PCB
1.6
1.2
0.8
0.4
0.0
0
the maximum junction temperature is 125C. The
junction to ambient thermal resistance, JA, is layout
dependent. For TSOT-23-8 (FC) package, the
thermal resistance, JA, is 56C/W on a standard
two-layer EVB test board. The maximum power
dissipation at TA = 25C can be calculated by the
following formula :
PD(MAX) = (125C  25C) / (56C/W) = 1.78W for
TSOT-23-8 (FC) package
The maximum power dissipation depends on the
operating ambient temperature for fixed TJ(MAX) and
thermal resistance, JA. The derating curve in Figure
5 allows the designer to see the effect of rising
ambient temperature
dissipation.
on
the maximum
power
25
50
75
100
125
Ambient Temperature (°C)
For recommended operating condition specifications,
Figure 5. Derating Curve of Maximum Power
Dissipation
Layout Consideration
The PCB layout is an important step to maintain the
high performance of RT4812.
Both the high current and the fast switching nodes
demand full attention to the PCB layout to save the
robustness of the RT4812 through the PCB layout.
Improper layout might show the symptoms of poor
line or load regulation, ground and output voltage
shifts, stability issues, unsatisfying EMI behavior or
worsened efficiency. For the best performance of the
RT4812, the following PCB layout guidelines must be
strictly followed.

Input/Output capacitors must be placed as close as
possible to the Input/Output pins.

SW should be connected to Inductor by wide and
short trace, keep sensitive components away from
this trace.

The feedback divider should be placed as close as
possible to the FB pin.
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RT4812
The feedback divider should be placed
as close as possible to the FB pin.
CIN
Input/Output capacitors
must be placed as close
as possible to the Input/
Output pins.
VIN
R2
COUT
8
ILIM
FB
2
7
EN
VOUT
3
6
SW
PGND
4
5
GND
L1
R1
VIN
SW should be connected to Inductor by wide and short
trace, keep sensitive components away from this trace.
Figure 6. PCB Layout Guide
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RT4812
Outline Dimension
Dimensions In Millimeters
Symbol
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.700
1.000
0.028
0.039
A1
0.000
0.100
0.000
0.004
B
1.397
1.803
0.055
0.071
b
0.220
0.380
0.009
0.015
C
2.591
3.000
0.102
0.118
D
2.692
3.099
0.106
0.122
e
0.585
0.715
0.023
0.028
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
TSOT-23-8 (FC) Surface Mount Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume
responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and
reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may
result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS4812-00
June 2015