Preliminary
RT9261/A
DS9261/A-03 January 2002
www.richtek.com
1
VFM Step-up DC/DC Converter
General Description
The RT9261 Series are VFM Step-up DC/DC ICs
with ultra low supply current by CMOS process and
suitable for use with battery-powered instruments.
The RT9261 IC consists of an oscillator, a VFM
control circuit, a driver transistor (LX switch), a
reference voltage unit, an error amplifier, resistors for
voltage detection, and a LX switch protection circuit.
A low ripple and high efficiency step-up DC/DC
converter can be constructed of this RT9261 IC with
only three external components.
The RT9261A IC provides with a drive pin (EXT) for
an external transistor, so that a power transistor can
be externally applied. Therefore, the RT9261A IC is
recommended for applications where large currents
are required. CE pin enables circuit to set the
standby supply current at a maximum of 0.5
A.
Ordering Information
RT9261A-
Features
Minimal Number of External Components ( Only
an inductor, a diode, and a capacitor)
Ultra Low Input Current ( 5
A at Switch Off)
2% High Output Voltage Accuracy
Low Ripple and Low Noise
Low Start-up Voltage, 0.85V at 1mA
75% Efficiency with Low Cost Inductor
+50 ppm/
C Low Temperature-Drift
SOT-89 and SOT-25 Small Packages
Applications
Power source for battery-powered equipment
Power source for cameras, camcorders, VCRs,
PDAs, pagers, electronic data banks, and hand-
held communication equipment
Power source for applications, which require
higher voltage than that of batteries used in the
appliances
Pin Configurations
Part Number
Pin Configurations
RT9261-
CX
(Plastic SOT-89)
TOP VIEW
1. GND
2. VOUT (TAB)
3. LX
RT9261A-
CX
(Plastic SOT-89)
TOP VIEW
1. GND
2. VOUT (TAB)
3. EXT
RT9261-
CB
(Plastic SOT-25)
TOP VIEW
1. CE
2. VOUT
3. NC
4.
GND
5.
LX
RT9261A-
CB
(Plastic SOT-25)
TOP VIEW
1. CE
2. VOUT
3. NC
4. GND
5. EXT
Operating temperature range
C: Commercial standard
Package type
B : SOT-25
X : SOT-89
Output voltage
15 : 1.5V
16 : 1.6V
:
49 : 4.9V
50 : 5.0V
A : Use external switch
Use internal switch
1
2
3
1
2
3
5
4
3
2
1
5
4
3
2
1
RT9261/A
Preliminary
www.richtek.com
DS9261/A-03 January 2002
2
Absolute Maximum Ratings
Output Voltage
8V
LX Pin Voltage
(1)
8V
EXT Pin Voltage
(2)
-0.3 to V
OUT
+0.3V
CE Pin Voltage
(3)
-0.3 to V
OUT
+0.3V
LX Pin Output Current
(1)
250mA
EXT Pin Current
(2)
50mA
Power Dissipation, P
D
@ T
A
= 25
C
SOT-89
0.5W
SOT-25
0.25W
Package Thermal Resistance
SOT-89,
JC
100
C/W
SOT-89,
JA
300
C/W
SOT-25,
JA
250
C/W
Operating Temperature Range
-20 to +85
C
Storage Temperature Range
165
C
Lead Temperature (Soldering, 10 sec.)
260
C
Notes:
(1) Applicable to RT9261-
CX and RT9261-
CB
(2) Applicable to RT9261A-
CX and RT9261A-
CB
(3) Applicable to RT9261-
CB and RT9261A-
CB
Electrical Characteristics
(Refer to Fig. 1)
Parameter
Symbol
Test Conditions
Min
Typ
Max Units
Output Voltage Accuracy
V
OUT
-2
--
+2
%
Input Voltage
V
IN
--
--
7
V
Start-up Voltage
V
ST
I
OUT
= 1mA, V
IN
: 0
2V
--
0.85
1.0
V
Hold-on Voltage
V
HO
I
OUT
= 1mA, V
IN
: 2
0V
0.7
--
--
V
V
OUT
3.5V
(1)
--
15
18
Input Current 1
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
at
no load
--
18
24
A
Input Current 2
To be measured at V
OUT
in switch off condition
--
5
8
A
V
OUT
3.5V
(1)
60
--
--
LX Switching Current
3.5V
<
V
OUT
5V
(2)
I
SWITCHING
V
LX
= 0.4V
80
--
--
mA
LX Leakage Current
I
LEAKAGE
V
LX
= 6V
--
--
0.5
A
Maximum Oscillator
F
MAX
80
120
160
KHz
Oscillator Duty Cycle
D
OSC
On ( V
LX
" L " ) side
65
75
85
%
Efficiency
--
75
--
%
V
LX
Voltage Limit
L
X
switch on
0.65
0.8
1.0
V
Notes:
(1) V
IN
= 1.8V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and External Circuit of Typical Application
(2) V
IN
= 3V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and External Circuit of Typical Application
Preliminary
RT9261/A
DS9261/A-03 January 2002
www.richtek.com
3
Electrical Characteristics
(Refer to Fig. 2)
Parameter
Symbol
Test Conditions
Min
Typ
Max Units
Output Voltage Accuracy
V
OUT
-2
--
+2
%
Input Voltage
V
IN
--
--
7
V
Start-up Voltage
V
ST
I
OUT
= 1mA, V
IN
: 0
2V
--
0.85
1.0
V
V
OUT
3.5V
(1)
--
30
50
Input Current 1
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
at no
load
--
60
90
A
V
OUT
3.5V
(1)
Input Current 2
3.5V
<
V
OUT
5V
(2)
To be measured at V
OUT
in
switch off condition
--
6
10
A
V
OUT
3.5V
(1)
-1.5
--
--
EXT "H" Output
Current
3.5V
<
V
OUT
5V
(2)
V
EXT
= V
OUT
0.4V
-2
--
--
mA
V
OUT
3.5V
(1)
1.5
--
--
EXT "L" Output
Current
3.5V
<
V
OUT
5V
(2)
V
EXT
= 0.4V
2
--
--
mA
Maximum Oscillator Frequency
F
MAX
80
120
160
KHz
Oscillator Duty Cycle
D
OSC
V
EXT
" H " side
65
75
85
%
Notes:
(1) Unless otherwise provided, V
IN
= 1.8V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and use External Circuit of
Typical Application
(2) Unless otherwise provided, V
IN
= 3V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and External Circuit of Typical
Application
RT9261/A
Preliminary
www.richtek.com
DS9261/A-03 January 2002
4
Electrical Characteristics
(Refer to Fig. 3)
Parameter
Symbol
Test Conditions
Min
Typ
Max Units
Output Voltage Accuracy
V
OUT
-2
--
+2
%
Input Voltage
V
IN
--
--
7
V
Start-up Voltage
V
ST
I
OUT
= 1mA, V
IN
: 0
2V
--
0.85
1.0
V
Hold-on Voltage
V
HO
I
OUT
= 1mA, V
IN
: 2
0V
0.7
--
--
V
V
OUT
3.5V
(1)
--
75
--
Efficiency
3.5V
<
V
OUT
5V
(2)
--
85
--
%
V
OUT
3.5V
(1)
--
15
18
Input Current 1
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
at
no load
--
18
24
A
V
OUT
3.5V
(1)
--
5
8
Input Current 2
3.5V
<
V
OUT
5V
(2)
To be measured at V
OUT
in switch off condition
--
6
10
A
V
OUT
3.5V
(1)
60
--
--
LX Switching
Current
3.5V
<
V
OUT
5V
(2)
I
SWITCHING
V
LX
= 0.4V
80
--
--
mA
LX Leakage Current
I
LEAKAGE
V
LX
= 6V
--
--
0.5
A
CE "H" Level
V
IN
= V
OUT
0.9
0.4
V
OUT
--
--
V
CE " L" Level
V
IN
= V
OUT
0.9
--
--
0.2
V
CE " H" Input Current
CE
= V
OUT
--
--
0.5
A
CE " L" Input Current
CE = 0V
-0.5
--
--
A
Maximum Oscillator Frequency
F
MAX
80
120
160
KHz
Oscillator Duty Cycle
D
OSC
On (V
LX
" L" ) side
65
75
85
%
V
LX
Voltage Limit
LX switch on
0.65
0.8
1.0
V
Notes:
(1) Unless otherwise provided, V
IN
= 1.8V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and use External Circuit of
Typical Application
(2) Unless otherwise provided, V
IN
= 3V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and External Circuit of Typical
Application
Preliminary
RT9261/A
DS9261/A-03 January 2002
www.richtek.com
5
Electrical Characteristics
(Refer to Fig. 4)
Parameter
Symbol
Test Conditions
Min
Typ
Max Units
Output Voltage Accuracy
V
OUT
-2
--
+2
%
Input Voltage
V
IN
--
--
7
V
Start-up Voltage
V
ST
I
OUT
= 1mA, V
IN
: 0
2V
--
0.85
1.0
V
V
OUT
3.5V
(1)
--
75
--
Efficiency
3.5V
<
V
OUT
5V
(2)
--
85
--
%
V
OUT
3.5V
(1)
--
30
50
Input Current 1
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
at
no load
--
60
90
A
V
OUT
3.5V
(1)
Input Current 2
3.5V
<
V
OUT
5V
(2)
To be measured at V
OUT
in
switch off condition
--
6
10
A
V
OUT
3.5V
(1)
-1.5
--
--
EXT "H" Output
Current
3.5V
<
V
OUT
5V
(2)
V
EXT
= V
OUT
0.4V
-2
--
--
mA
V
OUT
3.5V
(1)
1.5
--
--
EXT "L" Output
Current
3.5V
<
V
OUT
5V
(2)
V
EXT
= 0.4V
2
--
--
mA
CE "H" Level
V
IN
= V
OUT
0.9
0.4
V
OUT
--
--
V
CE " L" Level
V
IN
= V
OUT
0.9
--
--
0.2
V
CE " H" Input Current
CE
= V
OUT
--
--
0.5
A
CE " L" Input Current
CE = 0V
-0.5
--
--
A
Maximum Oscillator Frequency
F
MAX
80
120
160
KHz
Oscillator Duty Cycle
D
OSC
On (V
LX
" L" ) side
65
75
85
%
V
LX
Voltage Limit
LX switch on
0.65
0.8
1.0
V
Notes:
(1) Unless otherwise provided, V
IN
= 1.8V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and use External Circuit of
Typical Application
(2) Unless otherwise provided, V
IN
= 3V, VSS = 0V, I
OUT
= 10mA, T
OPT
= 25
C, and External Circuit of Typical
Application
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