CYT2708
CYT2708 Series Step-up DC-DC Converter
Description
CYT2708
Series
is a PFM Step-up DC/DC
converter IC with low supply current by CMOS
process. High frequency noise that occurs during
switching is reduced by using advanced circuit
designed, output voltage is programmable in 0.1V
steps
between
2.0~7.0V
and
maximum
frequency is 180KHz(Typ.). A low ripple, high
efficiency step-up DC/DC converter can be
constructed of CYT2708Xxx with only three
external components.
dissipation
CYT2708Xxx
is
During
Also available is a
power
mode.
with
shut-down
for
use
CE(chip enable) function that reduce
suitable
Features
Low ripple and low noise；
Operating voltage range：0.9V~8V；
Output voltage range：2.0V~7.0V(step
0.1V)；
Output voltage accuracy：±2.5%；
Output Current：if Vin=3.0V and Vout=5.0V，
thenIout=400mA；
Low start voltage：≤0.9V(at Iout=1mA)；
Maximum oscillator frequency：
180KHz(Typ.)；
High Efficiency：85%(Type)；
PACKAGE：SOT23，SOT89.
RoHS Compliant and 100% Lead (Pb)-Free
battery-powered instruments with low noise and
low supply current.
Selection Guide
Applications
Power source for battery-powered equipment；
Power source for wireless mouse, wireless
keyboard, toys, cameras, camcorders, VCRs,
PDAs, and hand-held communication
equipment；
Power source for appliances which require
higher cell voltage than that of batteries used in
the appliances。
TYPE
CYT2708Axx
CYT2708Bxx
CYT2708Cxx
CYT2708Dxx
CYT2708Fxx
POSTFIX
M3
P
M3
P
M5
P
M5
P
M5
PACKAGE
SOT23-3
SOT89-3
SOT23-3
SOT89-3
SOT23-5
SOT89-5
SOT23-5
SOT89-5
SOT23-5
SWITCHINGTRANSISTOR
Build_in
Transistor
Extemal
Transistor
Build_in
Transistor
Extemal
Transistor
ExtemalTransistor
CEFUNCTION
No
No
Yes
Yes
Yes
FEATURES
Lx
Ext
Lx+CE
Ext+CE
Ext
2008-7-14
SHENZHEN CYT OPTO-ELECTRONIC TECHNOLOGY CO.,LTD
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CYT2708
Pin Assignment
CYT2708Axx
PIN Number
SOT23-3
1
3
2
CYT2708Bxx
PIN Number
SOT23-3
1
3
2
CYT2708Cxx
SOT89-3
1
2
3
SOT89-3
1
2
3
PINNAME
Vss
Vout
Lx
FUNCTION
Ground
Output voltage monitor, IC internal power supply
Switch
PIN NAME
Vss
Vout
Ext
FUNCTION
Ground
Output voltage monitor, IC internal power supply
External switch transistor drive
PIN Number
SOT23-5
4
2
5
1
3
CYT2708Dxx
PIN Number
SOT23-5
4
2
5
1
3
CYT2708Fxx
PIN Number
SOT23-5
1
2
3
4
5
PIN NAME
SOT89-5
5
2
4
3
1
Vss
Vout
Lx
CE
NC
PIN NAME
SOT89-5
5
2
4
3
1
Vss
Vout
Ext
CE
NC
FUNCTION
Ground
Output voltage monitor, IC internal power supply
Switch
Chip enable
NC
FUNCTION
Ground
Output voltage monitor, IC internal power supply
External switch transistor drive
Chip enable
NC
PIN NAME
FB
Vdd
NC
Vss
EXT
FUNCTION
Feed Back
Output voltage monitor, IC internal power supply
NC
Ground
External switch transistor drive
2008-7-14
SHENZHEN CYT OPTO-ELECTRONIC TECHNOLOGY CO.,LTD
2
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CYT2708
CYT2708F
SYMB-OL
V
FB
V
start
V
hold
I
DD1
I
DD2
I
LX
I
LXleak
F
osc
Maxdty
EFFI
VFB=3.3V , Fosc=180kHz
PARAMETER
Output
Voltage
Oscillation
Voltage
Oscillation
Voltage
Supply Current 1
Supply Current 2
Lx Switching Current
Lx Leakage Current
Oscillation Frequency
Duty Ratio
Efficiency
Hold
Start-up
I
OUT
=1mA，V
IN
：0→2V
I
OUT
=1mA，V
IN
：2→0V
No external
component
Vout=Vout*0.95,
Vout=Vout+0.5V
V
LX
=0.4V,Vout=Vout*0.95
Vout=V
LX
=6V
Vout=set Vout*0.95
on(V
LX
“L＂)side
180
84
85
Feedback
CONDITIONS
MIN
3.22
TYP
3.3
0.8
0.45
80
10
360
MAX
3.38
0.9
UNITS
V
V
V
µA
µA
mA
0.5
µA
kHz
%
%
Note：1、Diode use Schottky diode such as IN5817 or IN5819 (forward voltage drop:0.2V)
2、
Inductor
：33μH（r<0.5Ω）
3、
Capacitor：Tantalum
type
100μF
Operation
CYT2708 step-up DC/DC converter charges energy in the inductor when Lx Transistor is on, and
discharges the energy with the addition of the energy from input power source thereto, so that a higher output
voltage than the input voltage is obtained. Following is the operation diagram.
Switching DC/DC Step up Converter operating process
2008-7-14
SHENZHEN CYT OPTO-ELECTRONIC TECHNOLOGY CO.,LTD
5
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