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IZ1937
White LED Step-Up Converter
(Functional equvalent of LT1937 Linear Technology Corporation)
Description
The IZ1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a
constant current. The device can drive two, three or four LEDs in series from a Li-Ion bat-
tery. Series connection of the LEDs provides identical LED currents resulting in uniform
brightness and eliminating the need for ballast resistors. The IZ1937 operates at 1.2MHz,
allowing the use of tiny external components. The output capacitor can be as small as
0.22uF, saving space and cost versus alternative solutions.
A low 95mV feedback voltage minimizes power loss in the current setting resistor for better
efficiency.
The device can used in mobile phones, PDAs, Handheld Computers, calculators, digital
cameras, MP3-players, GPS-receivers.
Features
Internally determined LED current
High Efficiency: 84% Typical
Drives Up to 4 LEDs from a 3.2V Supply
Drives Up to 6 LEDs from a 5V Supply
36V rugged bipolar switch
Fast 1.2MHz switching frequency
Uses tiny 1mm Tall Inductors
Requires only 0.22uF output capacitor
ICs are available for shipment in chip form on unsawn wafers
Tab 1. Contact Pad Description
Contact pad number
Symbol
Description
01 SW Switch pad (Pin)
02
GND
Common pad (pin)
03 VIN Input supply pad (pin)
04
SHDN
Shutdown pad (pin)
05
GND
Common pad (pin)
06 FB Feedback pad (pin)
1 Ver.1.0/9.02.2008
IZ1937-TSe.doc

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IZ1937
VIN
03
Reference
voltage
source
FB
06
A1
R1 -
A3
-
+ R3
+
R2 A2
C1
SHDN
04
A1 – error amplifier;
A2 – addrer;
A3 – PWM – comprator;
A4 – comparator;
A5 –driver;
C1 – capacitor;
R1 – R4 – resistor;
VT1 – transistor
Sawtooth
voltage
generator
Oscilator
SW
01
RS -
-flip-flops
A5
A4
+
VT1
R4
-
02,05
GND
Te device contain, switch on/off circuit; output current overrising protection unit, driver-buffer,
output switch.
Fig.1 Block Diagram
2 Ver.1.0/9.02.2008
IZ1937-TSe.doc

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Table 2 –Absolute maximum ratings
Symbol Parameter
UIN
USW
UFB
U SHDN
TJ
Тstg
Input voltage
SW pin Voltage
FB pin Voltage
SHDN pin Voltage
Storage Temperature
Junction Temperature
IZ1937
Absolute
maximum ratings
Min.
Max.
- 10
- 36
- 10
- 10
- 150
-60 150
Unit
V
V
V
V
oC
oC
Table 3 – Recommended operating mode
Symbol Parameter
UIN Input voltage
TJ Storage Temperature
Recommended
operating mode
Min.
Max.
2,5 10
- 125
Unit
V
oC
Table 4 Electric Parameters
Parameter, unit
Symbol
Minimum input voltage, V
Maximum input voltage, V
Feedback Voltage, mV
UIN MIN
UIN MAX
UFB
FB pad Bias Current, nA
Supply Current,
mA
uA
Switching Frequency, MHz
Maximum Duty Cycle, %
Switch Leakage Current, uA
IFB
IQ
fS
DCMAX
ILSW
Value
Min. Max.
2,5 -
2,5
- 10
10
86 104
76 114
10 100
10 150
- 2,5
3,75
- 1,0
2,0
0,8 1,6
0,6 1,8
85 -
80
- 5,0
7,5
Testing mode
U SHDN = 3,0 V
Ambient
temperature, °C
UIN = 3,0 V,
U SHDN = 3,0 V,
ISW = 100 mA
Duty Cycle 66 %
UIN = 3,0 V,
U SHDN = 3,0 V
UIN = 3,0 V,
U SHDN = 3,0 V
UIN = 3,0 V,
U SHDN = 0 V
UIN = 3,0 V,
U SHDN = 3,0 V
UIN = 3,0 V,
U SHDN = 3,0 V
UIN = 3,0 V, U SHDN =3,0V,
USW = 5,0 V
25 ± 10
-40 … +125
3 Ver.1.0/9.02.2008
IZ1937-TSe.doc