Preliminary
RT9261B
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.
Features
Minimal Number of External Components
(Only an Inductor, a Diode, and a Capacitor)
Ultra Low Input Current (6.5µA at Switch Off)
µ
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
The CE pin enables the circuit to set the standby
supply current at a maximum of 0.5µA.
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
Ordering Information
RT9261B-
Package type
B : SOT-25
X : SOT-89
Operating temperature range
C: Commercial standard
Output voltage
15 : 1.5V
16 : 1.6V
:
49 : 4.9V
50 : 5.0V
Pin Configurations
Part Number
RT9261B-
CX
1
2
3
Pin Configurations
TOP VIEW
1. GND
2. VOUT (TAB)
3. LX
TOP VIEW
5
4
(Plastic SOT-89)
RT9261B-
CB
(Plastic SOT-25)
1
2
3
CE
VOUT
NC
GND
5.
LX
1.
2.
3.
4.
DS9261B-03 September 2001
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1
RT9261B
Typical Application Circuit
Preliminary
D1
L1
V
IN
27
µ
H
1N5819
RT9261B
LX
VOUT
GND
V
OUT
+
-
Co
22
µ
F
D1
L1
V
IN
27
µ
H
1N5819
RT9261B
LX
VOUT
CE
GND
V
OUT
+ Co
-
22
µ
F
* L1 ranges from 27µH to 120µH
Pin Description
Pin No.
-xxCX
1
2
3
--
--
-xxCB
4
2
5
1
3
Pin Name
GND
VOUT
LX
CE
NC
Ground
Output Voltage
Pin for Switching
Chip Enable (Active High)
No Connection
Pin Function
Function Block Diagram
LX
LXSW
Buffer
GND
VFM Control
OSC 190kHz
Chip Enable
-
+
Error Amp.
VOUT
VLX Limiter
Vref
CE
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DS9261B-03 September 2001
2
Preliminary
Absolute Maximum Ratings
Output Voltage
LX Pin Voltage
CE Pin Voltage
(1)
RT9261B
8V
8V
-0.3 to V
OUT
+0.3V
400mA
0.5W
0.25W
100°C/W
300°C/W
250°C/W
-20 to +85°C
-65°C to 150°C
260°C
LX Pin Output Current
Power Dissipation, P
D
@ T
A
= 25°C
SOT-89
SOT-25
Package Thermal Resistance
SOT-89,
θ
JC
SOT-89,
θ
JA
SOT-25,
θ
JA
Operating Temperature Range
Storage Temperature Range
Lead Temperature (Soldering, 10 sec.)
Notes: (1) Applicable to RT9261B-xxCB
Electrical Characteristics
(Refer to Fig. 1)
Parameter
Output Voltage Accuracy
Input Voltage
Start-up Voltage
Hold-on Voltage
Input Current 1
(1) (2)
(1)
(2)
(1)
(2)
Symbol
∆V
OUT
V
IN
V
ST
V
HO
Test Conditions
Min
-2
--
--
0.7
--
--
--
--
--
120
160
--
140
65
--
0.65
Typ
--
--
0.8
--
24
36
6.5
18
20
--
--
--
190
75
80
0.8
Max Units
+2
7
1
--
36
45
10
36
45
--
--
0.5
240
85
--
1.0
µA
%
V
V
V
µA
µA
I
OUT
= 1mA, V
IN
: 0
→
2V
I
OUT
= 1mA, V
IN
: 2
→
0V
To be measured at V
IN
in
continuous switching
To be measured at V
OUT
in
switch off condition
V
OUT
≤
3.5V
3.5V
<
V
OUT
≤
5V
Input Current 2
Input Current 3
V
OUT
≤
3.5V
3.5V
<
V
OUT
≤
5V
LX Switching Current
LX Leakage Current
Maximum Oscillator Frequency
Oscillator Duty Cycle
Efficiency
V
LX
Voltage Limit
Notes:
V
OUT
≤
3.5V
(1)
To be measured at V
IN
in
no load (guaranteed by I
1
and I
2
)
I
SWITCHING
V
LX
= 0.4V
I
LEAKAGE
F
MAX
D
OSC
On (V
LX
“L”) side
LX switch on
V
LX
= 6V
3.5V
<
V
OUT
≤
5V
(2)
mA
µA
KHz
%
%
V
(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
DS9261B-03 September 2001
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3
RT9261B
Parameter
Output Voltage Accuracy
Input Voltage
Start-up Voltage
Hold-on Voltage
Efficiency
Input Current 1
(1) (2)
(1)
(2)
Preliminary
Electrical Characteristics
(Refer to Fig. 2)
Symbol
∆V
OUT
V
IN
V
ST
V
HO
V
OUT
≤
3.5V
I
OUT
= 1mA, V
IN
: 0
→
2V
I
OUT
= 1mA, V
IN
: 2
→
0V
Test Conditions
Min
-2
--
--
0.7
--
To be measured at V
IN
in
continuous switching
To be measured at V
OUT
in switch off condition
V
OUT
≤
3.5V
(1)
(2)
Typ
--
--
0.8
--
80
24
36
6.5
18
20
--
--
--
--
--
--
--
190
75
0.8
Max Units
+2
7
1
--
--
36
45
10
36
45
--
--
0.5
--
0.2
0.5
--
240
85
1.0
µA
%
V
V
V
%
µA
µA
--
--
--
--
--
120
160
--
0.4×V
OUT
--
--
-0.5
140
65
0.65
3.5V
<
V
OUT
≤
5V
Input Current 2
Input Current 3
3.5V
<
V
OUT
≤
5V
LX Switching Current
LX Leakage Current
CE “H” Level
CE “L” Level
CE “H” Input Current
CE “ L” Input Current
Maximum Oscillator Frequency
Oscillator Duty Cycle
V
LX
Voltage Limit
Notes:
V
OUT
≤
3.5V
(1)
To be measured at V
IN
in
no load (guaranteed by I
1
and I
2
)
I
SWITCHING
V
LX
= 0.4V
I
LEAKAGE
V
LX
= 6V
V
IN
= V
OUT
* 0.9
V
IN
= V
OUT
* 0.9
CE = V
OUT
CE = 0V
F
MAX
D
OSC
On (V
LX
“L”) side
LX switch on
3.5V
<
V
OUT
≤
5V
(2)
mA
µA
V
V
µA
µA
KHz
%
V
(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
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DS9261B-03 September 2001
4
Preliminary
Typical Operating Charateristics
Start-up/Hold-on Voltage vs. Output Current
Start-up/Hold-on Voltage Vstart/Vhold (V)
2.5
4.0
3.5
2
RT9261B
Output Voltage vs. Output Current
3.0V
2.5V
2.0V
Output Voltage (V)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
1.0V
1.5V
1.5
V
start
V
hold
0.5
V
OUT
= 3.3V
L = 47uH
0
30
60
90
120
150
180
1
0
V
OUT
= 3.3V
L = 47uH
50
100
150
200
Output Current (mA)
Output Current (mA)
Output Current vs. Ripple Voltage
300
2.5V
250
2.0V
90
80
Output Current vs. Ripple Voltage
3.0V
2.0V
Ripple Voltage (mVp-p)
200
150
100
50
1.0V
0
0
50
100
1.5V
V
OUT
= 3.3V
C
OUT
= 20uF
L = 47uH
150
200
Ripple Voltage (mVp-p)
3.0V
70
60
50
40
30
20
10
0
0
50
100
1.0V
1.5V
V
OUT
= 3.3V
C
OUT
= 68uF
L = 47uH
150
200
2.5V
Output Current (mA)
Output Current (mA)
Output Current vs. Ripple Voltage
25
90
80
Efficiency vs. output Current
3.0V
2.5V
1.0V
1.5V
2.0V
Ripple Voltage (mVp-p)
20
2.5V
15
3.0V
70
Efficiency (%)
60
50
40
30
20
10
0
0
50
100
10
1.0V
5
2.0V
1.5V
0
50
100
V
OUT
= 3.3V
C
OUT
= 170uF
L = 47uH
150
200
0
V
OUT
= 3.3V
L = 47uH
150
200
Output Current (mA)
Output Current (mA)
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DS9261B-03 September 2001
5
