Preliminary
RT9261B
DS9261B-03 September 2001
www.richtek.com
1
VFM Step-up DC/DC Converter
General Description
The RT9261B Series are VFM Step-up DC/DC
converter ICs with ultra low supply current by CMOS
process and suitable for use with battery-powered
instruments.
The RT9261B 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 with the
RT9261B IC and only three external components.
The CE pin enables the circuit to set the standby
supply current at a maximum of 0.5
A.
Ordering Information
RT9261B-
Features
Minimal Number of External Components
(Only an Inductor, a Diode, and a Capacitor)
Ultra Low Input Current (6.5
A at Switch Off)
Capable of Supplying 50mA Output Current
with Internal Switch
2% Output Voltage Accuracy
Low Ripple and Low Noise
Low Start-up Voltage, 0.8V at 1mA
80% 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 appliances, which require
higher voltage than that of batteries used in the
appliances
Pin Configurations
Part Number
Pin Configurations
RT9261B-
CX
(Plastic SOT-89)
TOP VIEW
1. GND
2. VOUT (TAB)
3. LX
RT9261B-
CB
(Plastic SOT-25)
TOP VIEW
1. CE
2. VOUT
3. NC
4. GND
5.
LX
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
1
2
3
5
4
3
2
1
Preliminary
RT9261B
DS9261B-03 September 2001
www.richtek.com
3
Absolute Maximum Ratings
Output Voltage
8V
LX Pin Voltage
8V
CE Pin Voltage
(1)
-0.3 to V
OUT
+0.3V
LX Pin Output Current
400mA
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
-65
C to 150
C
Lead Temperature (Soldering, 10 sec.)
260
C
Notes: (1) Applicable to RT9261B-xxCB
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
--
0.8
1
V
Hold-on Voltage
V
HO
I
OUT
= 1mA, V
IN
: 2
0V
0.7
--
--
V
V
OUT
3.5V
(1)
--
24
36
Input Current 1
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
in
continuous switching
--
36
45
A
Input Current 2
(1) (2)
To be measured at V
OUT
in
switch off condition
--
6.5
10
A
V
OUT
3.5V
(1)
--
18
36
Input Current 3
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
in
no load (guaranteed by I
1
and I
2
)
--
20
45
A
V
OUT
3.5V
(1)
120
--
--
LX Switching Current
3.5V
<
V
OUT
5V
(2)
I
SWITCHING
V
LX
= 0.4V
160
--
--
mA
LX Leakage Current
I
LEAKAGE
V
LX
= 6V
--
--
0.5
A
Maximum Oscillator Frequency
F
MAX
140
190
240
KHz
Oscillator Duty Cycle
D
OSC
On (V
LX
"L") side
65
75
85
%
Efficiency
--
80
--
%
V
LX
Voltage Limit
LX switch on
0.65
0.8
1.0
V
Notes:
(1) V
IN
= 1.8V, V
SS
= 0V, I
OUT
= 1mA, Topt = 25
C, and External Circuit of Typical Application
(2) V
IN
= 3V, V
SS
= 0V, I
OUT
= 1mA, Topt = 25
C, and External Circuit of Typical Application
RT9261B
Preliminary
www.richtek.com
DS9261B-03 September 2001
4
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
--
0.8
1
V
Hold-on Voltage
V
HO
I
OUT
= 1mA, V
IN
: 2
0V
0.7
--
--
V
Efficiency
--
80
--
%
V
OUT
3.5V
(1)
--
24
36
Input Current 1
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
in
continuous switching
--
36
45
A
Input Current 2
(1) (2)
To be measured at V
OUT
in switch off condition
--
6.5
10
A
V
OUT
3.5V
(1)
--
18
36
Input Current 3
3.5V
<
V
OUT
5V
(2)
To be measured at V
IN
in
no load (guaranteed by I
1
and
I
2
)
--
20
45
A
V
OUT
3.5V
(1)
120
--
--
LX Switching Current
3.5V
<
V
OUT
5V
(2)
I
SWITCHING
V
LX
= 0.4V
160
--
--
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
140
190
240
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) V
IN
= 1.8V, V
SS
= 0V, I
OUT
= 1mA, Topt = 25
C, and External Circuit of Typical Application
(2) V
IN
= 3V, V
SS
= 0V, I
OUT
= 1mA, Topt = 25
C, and External Circuit of Typical Application
Preliminary
RT9261B
DS9261B-03 September 2001
www.richtek.com
5
Typical Operating Charateristics
Output Current vs. Ripple Voltage
0
50
100
150
200
250
300
0
50
100
150
200
Output Current (mA)
R
i
p
p
l
e V
o
l
t
a
g
e (
m
V
p
-
p
)
V
OUT
= 3.3V
C
OUT
= 20uF
L = 47uH
1.0V
1.5V
2.0V
2.5V
3.0V
Output Current vs. Ripple Voltage
0
10
20
30
40
50
60
70
80
90
0
50
100
150
200
Output Current (mA)
R
i
p
p
l
e V
o
l
t
a
g
e (m
V
p
-p
)
V
OUT
= 3.3V
C
OUT
= 68uF
L = 47uH
1.0V
1.5V
2.0V
2.5V
3.0V
Output Current vs. Ripple Voltage
0
5
10
15
20
25
0
50
100
150
200
Output Current (mA)
R
i
p
p
l
e V
o
l
t
a
g
e (
m
V
p
-
p
)
V
OUT
= 3.3V
C
OUT
= 170uF
L = 47uH
1.0V
1.5V
2.0V
2.5V
3.0V
Start-up/Hold-on Voltage vs. Output Current
0
0.5
1
1.5
2
2.5
0
30
60
90
120
150
180
Output Current (mA)
S
t
a
r
t-
u
p
/
H
o
l
d
-
o
n
Vo
l
t
a
g
e
Vs
ta
r
t/Vh
o
l
d
(
V
)
V
OUT
= 3.3V
L = 47uH
V
start
V
hold
Efficiency vs. output Current
0
10
20
30
40
50
60
70
80
90
0
50
100
150
200
Output Current (mA)
E
f
f
i
ci
e
n
cy
(
%
)
V
OUT
= 3.3V
L = 47uH
1.0V
1.5V
2.0V
2.5V
3.0V
Output Voltage vs. Output Current
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
50
100
150
200
Output Current (mA)
O
u
t
put
V
o
l
t
a
g
e
(
V
)
V
OUT
= 3.3V
L = 47uH
1.0V
1.5V
2.0V
2.5V
3.0V
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