LM3557 Datasheet, PDF (3/19 Pages) National Semiconductor (TI) – Step-Up Converter for White LED Applications

LM3557
www.ti.com
SNVS338B – NOVEMBER 2004 – REVISED FEBRUARY 2013
Operating Conditions ^{(1) (2)}
Junction Temperature (T_J) Range
Ambient Temperature (T_A) Range
Supply Voltage, V_IN Pin
En Pin
−40°C to +125°C
−40°C to +85°C
2.7V to 7.5V
0V to V_IN +0.4V
(1) Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical characteristic specifications do not
apply when operating the device outside of its rated operating conditions.
(2) All voltages are with respect to the potential at the GND pin.
THERMAL CHARACTERISTICS⁽¹⁾⁽²⁾
over operating free-air temperature range (unless otherwise noted)
Junction-to-Ambient Thermal
55°C/W
Resistance (θ_JA), WSON Package
(1) The maximum allowable power dissipation is a function of the maximum junction temperature, T_J(MAX), the junction-to-ambient thermal
resistance, θ_JA, and the ambient temperature, T_A. See Thermal Properties for the thermal resistance. The maximum allowable power
dissipation at any ambient temperature is calculated using: P_D(MAX) = (T_J(MAX) – T_A)/θ_JA. Exceeding the maximum allowable power
dissipation will cause excessive die temperature.
(2) Junction-to-ambient thermal resistance (θ_JA) is taken from a thermal modeling result, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. The test board is a 4 layer FR-4 board measuring 102 mm x 76 mm x 1.6 mm with a 2 x 1 array
of thermal vias. The ground plane on the board is 50 mm x 50 mm. Thickness of copper layers are 36 µm/18 µm/18 µm/36 µm (1.5 oz/1
oz/1 oz/1.5 oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W. In applications where high maximum power
dissipation exists, special care must be paid to thermal dissipation issues. For more information on these topics, please refer to
Application Note 1187: Leadless Leadframe Package (LLP) and the Layout Guidelines section of this datasheet.
Electrical Characteristics ^{(1) (2)}
Limits in standard typeface are for T_J = 25°C. Limits in bold typeface apply over the full operating junction temperature range
(−40°C ≤ T_J ≤ +125°C). Unless otherwise specified: V_IN = 3.6V.
Parameter
Test Conditions
Min
Typ
Max
Units
V_IN
Input Voltage
I_Q
Quiescent Current
V_EN = 0V (Shutdown)
V_EN = 1.8V; V_OVP = 27V
(Non-Switching)
2.7
7.5
V
0.01
2
µA
0.55
0.8
mA
En
Device Enable Threshold
Device On
Device Off
I_CL
Power Switch Current Limit ⁽³⁾
V_IN = 3V
0.9
0.3
V
0.4
0.8
1.1
0.55
0.8
1.02
A
R_DS(ON)
TC (R_DS(ON))
OVP
Power Switch ON Resistance
R_DS(ON) Temperature Coefficient
Over-Voltage Protection ⁽⁴⁾
UVP
Under-Voltage Protection ⁽⁴⁾
I_Sw1 = 175 mA
On Threshold
Off Threshold
On Threshold
Off Threshold
800
1000
mΩ
0.5
%/C
22
26
28.5
21.5
25.5
28
V
2.2
2.3
V
I_OVP
I_EN
F_S
V_Fb-Sw2
I_Fb
D_MAX
Over-Voltage Protection Pin Bias
Current ⁽⁵⁾
Enable Pin Bias Current ⁽⁵⁾
Switching Frequency
Feedback Pin Voltage ⁽⁶⁾
Feedback Pin Bias Current ⁽⁵⁾
Maximum Duty Cycle
V_EN = 1.8V
V_IN = 3V
V_IN = 3V
4
10
µA
0.8
3
µA
0.9
1.25
1.6
MHz
0.459
0.51
0.561
V
0.03
2
µA
85
90
%
(1) All voltages are with respect to the potential at the GND pin.
(2) Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the
most likely norm.
(3) The Power Switch Current Limit is tested in open loop configuration. For closed loop application current limit please see the Current
Limit vs Temperature performance graph.
(4) The on threshold indicates that the LM3557 is no longer switching or regulating LED current, while the off threshold indicates normal
operation.
(5) Current flows into the pin.
(6) Feedback pin voltage is with respect to the voltage at the Sw2 pin.
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