LR1937S

LESHAN RADIO COMPANY, LTD.
White LED Step-Up Converter
LR1937S
LR1937S is a step-up DC/DC converter
specifically designed to drive white LED with a
constant current. It can drive two, three, or four
LEDS. It switches at 1.2MHz and use tiny
external components. The output capacitor can
be as small as 0.22uF, which can save space
and cost versus alternative solutions. Feedback
voltage
is
as
low
as
273mV.
Built-in
¾
¾
¾
¾
¾
¾
¾
¾
¾
OverVoltage, UVLO Function
Fast 1.2MHz Switching Frequency
Requires Only 0.22uF Output Capacitor
Inherently Matched LED Current
High Efficiency: 85% Typical
2.5V to 10V VIN ranges
Drives Up to Four series LEDs with a Li-lon cell
Uses Very Tiny Inductors
TSOP-6 Package
OverVoltage, UVLO function.
Absolute maximum ratings
Parameter
symbol
value
unit
Supply Voltage
VIN
10
V
Feedback Voltage
FB
10
V
Switch Voltage
SW
30
V
CE Voltage
VCE
10
V
Operating temperature range
Topr
-25 to +70
℃
Storage temperature range
Rstg
-65 to +150
℃
Junction temperature
Tj
125
℃
Pin name
Description
1： Switch
1
6
2
5
3
4
Symbol
SW
Description
6：Supply
Symbol
VIN
Voltage
2：GND
3：Feedback
GND
FB
5：Over
Voltage
OVP
4：Start-Up
CE
Page 1 of 8
LESHAN RADIO COMPANY, LTD.
Block Diagram
PIN1(SW)
PWM
CONTROL
PIN5(OVP)
CURRENT SENSE
+
SLOPE COMP
Fosc
+
0
0
-
PIN6(VIN)
VREF
0
PIN2(GND)
+
gm
-
SHUTDOWN
+
PIN4
PIN3(FB)
LR1937S
Page 2 of 8
LESHAN RADIO COMPANY, LTD.
Electrical Characteristics
Tamb = 25℃, VIN=3V，VCE=3V,unless otherwise specified.
Parameter
Test Conditions / Pins
Min
Minimum Operating Voltage
Type
Max
2.5
V
Maximum Operating Voltage
ISW=100mA,
Feedback Voltage
Duty Cycle=66%
10
V
250
270
290
mV
50
100
200
nA
1.9
2.5
mA
0.1
1
uA
1.6
MHz
FB Pin Bias Current
Supply Current
Unit
VCE=0V
Switching Frequency
0.8
1.2
Maximum Duty Cycle
85
90
OVP Protection
27
30
Switch Current Limit
33
mA
mV
ISW =250mA
350
Switch Leakage Current
VSW=5V
0.01
5
1.5
uA
V
CE Voltage Low
CE Pin Bias Current
V
320
Switch VCESAT
CE Voltage High
%
60
120
0.4
V
180
uA
Typical Application
1
HI
L1
2
22uH
VCC
6
Vin
C1
1u
5
OVP
1
SW
D4
1
2
D1
ME1937S
LR1937S
LR1937S
4
CE
3
CS
2
GND
C2
0.47u
D2
D3
18Ω
Page 3 of 8
LESHAN RADIO COMPANY, LTD.
Analog Voltage Light Control
L1
1
HI
2
22uH
VCC
D4
1
Vin
OVP
2
SW
D1
LR1937S
MLR1937S
E1937S
C1
1u
CE
CS
C2
0.47u
GND
D2
D3
5K
90K
18Ω
HI
VDC
Logic Voltage Light Control
1
HI
L1
2
22uH
VCC
D4
C1
1u
Vin
OVP
SW
1
2
D1
MLR1937S
E1937S
LR1937S
HI
CE
CS
GND
C2
0.47u
D2
PWM
D3
1k
18Ω
Page 4 of 8
LESHAN RADIO COMPANY, LTD.
Characteristics Curve
Iq Vs T
Iq(mA)
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2 0
-50
100
25
2
4
6
10
8
Vin(V)
Switch Frequency（MHz）
Switch Frequency
Vs
T
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-25
0
25
50
75
100
T（°C）
Page 5 of 8
LESHAN RADIO COMPANY, LTD.
η（%）
η VS T
84.5
84
83.5
83
82.5
82
81.5
81
80.5
80
ILED=10mA
ILED=15mA
ILED=20mA
-25
0
25
50
75
100
T（°C）
η（%）
Drive 2LED
86
84
82
80
78
76
74
72
70
Vin=3.6V
Vin=3V
0
10
20
ILED(mA)
30
40
Page 6 of 8
LESHAN RADIO COMPANY, LTD.
Drive 3LED
90
η（%）
85
80
Vin=3V
Vin=3.6V
75
70
65
60
0
5
10
ILED（mA）
15
20
UVLO
18
16
14
ILED＝VFB/R1
ILED(mA)
12
10
8
6
4
2
0
-2 0
2
4
6
8
10
Vin(V)
Page 7 of 8
LESHAN RADIO COMPANY, LTD.
TSOP-6
Dimension
Page 8 of 8