LC101N

LC101N SANKEN

Document overview

• PDF pages: 15

Technical content

Page 1

LED Current balancer IC

Description

LC101N is a current control IC that uses a low-saturated PNP bipolar transistor in the power block. The saturation voltage of the saturated condition is small and can be designed with minimal losses in the case of driving with a constant current source. The constant current value is set up by the resistor connected between the FB terminal and the LO pin, and you can drive the LED in the constant current condition. LC101N is available in an 8-pin DFN package for surface mounting.

Features

• Maximum current is 150 mA
• Low input-output voltage difference design is achieved by low saturation voltage; VDIF(max.)＝0.35 V (Io = 150 mA)
• Reference voltage of 200 mV reduces the sense resistor loss
• Optimal balance operation can be realise in parallel connection of multiple LED strings
• Protections Overcurrent Protection (OCP): Foldback Thermal Shutdown (TSD): Auto-restart

Typical Application

Data Sheet

Package

DFN 8

\*Not to scale

Electrical Characteristics

• Maximum input voltage: 35 V
• Maximum output current: 150 mA
• Reference voltage for the constant current control: 200 mV
• Power Dissipation: 1.3 W

Applications

• LED Lightings
• Back light system for LCD-Touch-panels,etc.

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CONTENTS

Description ------------------------------------------------------------------------------------------------------ 1

CONTENTS ---------------------------------------------------------------------------------------------------- 2

1. Absolute Maximum Ratings ----------------------------------------------------------------------------- 3 2. Recommended Operating Conditions ----------------------------------------------------------------- 3 3. Electrical Characteristics -------------------------------------------------------------------------------- 3 4. Thermal Resistance --------------------------------------------------------------------------------------- 3 5. Derating Curve -------------------------------------------------------------------------------------------- 4 6. Block Diagram --------------------------------------------------------------------------------------------- 5

1. Pin Configuration Definitions --------------------------------------------------------------------------- 5 8. Typical Application --------------------------------------------------------------------------------------- 6 9. External Dimensions -------------------------------------------------------------------------------------- 7 10. Marking Diagram ----------------------------------------------------------------------------------------- 7 11. Operational Description --------------------------------------------------------------------------------- 8 11.1 Basic operation --------------------------------------------------------------------------------------- 8

11.2 Power Supply----------------------------------------------------------------------------------------- 8 11.3 Current Balance Operation ----------------------------------------------------------------------- 8 11.4 Operable voltage of LC101N ---------------------------------------------------------------------- 9 11.5 Overcurrent Protection (OCP) ------------------------------------------------------------------- 9 11.6 Thermal Shutdown (TSD) ------------------------------------------------------------------------- 9 12. Design Notes ------------------------------------------------------------------------------------------------ 9 12.1 External Components ------------------------------------------------------------------------------ 9

12.1.1 LED current setup resistor, R1 ------------------------------------------------------------- 9 12.2 Pattern Layout ------------------------------------------------------------------------------------- 10 12.2.1 PCB Trace Layout and Component Placement --------------------------------------- 10 12.2.2 Pattern Layout Example ------------------------------------------------------------------- 10 12.2.3 Land Pattern Example --------------------------------------------------------------------- 11 13. Typical Performance Curves -------------------------------------------------------------------------- 11 14. Packing Specifications ---------------------------------------------------------------------------------- 12

14.1 Emboss and Carrier Tape Specification ------------------------------------------------------ 12 14.2 Reel Specifications -------------------------------------------------------------------------------- 13 15. Recommended Reflow Temperature Profile ------------------------------------------------------- 14

IMPORTANT NOTES ------------------------------------------------------------------------------------- 15

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1. Absolute Maximum Ratings

• Unless otherwise specified TA = 25 °C, the LO pin is reference voltage level.

\* When the junction temperature of the IC becomes 110 °C (min.) or more, the thermal shutdown (TSD) activates.

2. Recommended Operating Conditions

• Unless otherwise specified TA = 25 °C, the LO pin is reference voltage level.

\* Since the between VIN and ILED has following relationship, the value of VIN is different by condition. Allowable power dissipation, PD is calculated by Figure 5-1.

PD(MAX) = (VIN − VLED) × ILED(MAX)

(1)

3. Electrical Characteristics

• Unless otherwise specified TA = 25 °C, the LO pin is reference voltage level.

(1) Design assurance. (2) The saturation voltage between the IN pin and the LED pin.

4. Thermal Resistance

• Unless otherwise specified TA = 25 °C, the LO pin is reference voltage level.

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5. Derating Curve

Figure 5-1 shows the thermal derating curve that the IC is mounted on the pattern layout example of Section 12.2.2, and is calculated based on the junction temperature 110 ° C. When the junction temperature becomes 110 ° C or more, thermal shutdown might be activated.

1.4

1.2

0.8

0.6

0.4

0.2

-20 0 20 40 60 80 100 120

Ambient temperature, TA (°C)

Figure 5-1 Thermal Derating Curve

• Junction Temperature Calculation The junction tenperature,Tj is calucrated by using Equation (2)

Tj = PD × θj-TOP＋TTOP (°C)

(2)

where, θj-TOP = 27 °C/W and TTOP is the measurement temperature of marking surface.

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6. Block Diagram

7. Pin Configuration Definitions

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1. Typical Application

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1. External Dimensions

• DFN8

<Top View>

<Bottom View>

• Dimension is in millimeters
• Pb-free. Device composition compliant with the RoHS directive
• Width of 1 pin is 0.375 mm, the others are 0.3mm
• In order to release temperrature The heat slug of the back surface should heat dissipation to the pattern of PCB.

1. Marking Diagram

Abbreviated product number (LC101N)

Lot Number Y = Last Digit of Year (0~9) M = Month (1~9, O, N or D) D = Period of days (1~9 or A~Z without B, I, O and Q)

Control Number

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11. Operational Description

11.1 Basic operation

The current control of the LC101N is quite simple. The both end voltage of the setup resistor R1 which is connected between the FB terminal and the LO pin. So that it becomes constant, the emitter-collector voltage of the internal PNP-transistor is linear-controlled by the error amplifier. Figure 11-1 shows the basic circuit of LC101N.

Figure 11-1 LC101N basic circuit

LED current, ILED is calculated by Equation (3).

(3)

From Equation (3), the setup resistor, R1 is calculated by Equation (4).

(4)

The reference voltage, VFB for the constant current control is 200 mV. The both end voltage of R1 is controlled to become equal to VFB.

The loss of R1, PR1 is calculated by Equation (5).

(5)

Table 11-1 shows the calculation result of relationship of ILED, R1, and PR1.

Table 11-1 The loss of R1, PR1

In addition, the loss of the IC, PD is calculated by Equation (6).

(6)

where, VIN is the voltage between the IN pin and the LO pin, and VLED is the voltage between the LED pin and LO pin.

11.2 Power Supply

The power supply should be use the constant-current source. If the constant-voltage source is used, the voltage difference between input and output that does not require for LED becomes the loss of the IC. Though it will operate with the constant-voltage source, if the input-output voltage difference becomes larger than necessary, and all of surplus will be loss in this IC The ability of power supply, PIN is required to satisfy following equation.

(7)

where, N is number of LED in series, VF is forward voltage of LED, and ICONST is the constant current of power supply.

For example, LED current is set to 50 mA in Figure 11-1. The constant current of power supply, ICONST, is set fewer than the total current value of LED-strings A and B (100mA), because the drooping characteristic of constant-current source is considered. In this case, ICONST is set 95 mA. If VF = 3V and n = 7, PIN becomes as follows:

11.3 Current Balance Operation

If All LEDs have same VF, and the same current flows to LED-string A and B, the power loss of IC becomes minimum because the circuit is controlled by the constant-current source, ICONST and the internal transistor is a saturated condition. However, the complete equilibrium state is impossible by characteristic variations of VF. If each VF2 of LED string B is smaller than VF1 of LED string A by 0.1 V.

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. In this case,

is applied to between the IN pin and the LED pin of LC101N. Since the LED string B current, ILED2, is controlled to constant by R2, the loss of LC101N of LED string B side is following value, and is enough acceptable value.

If it is operated in the constant current source, the voltage applied to the LED string, it becomes the minimum requirement value of the LED-string with the highest VF. When the constant current source is used, the necessary voltage for LED string with the highest total VF is supplied. Thus, LC101N reduces the current concentration by VF fluctuation and, the brightness unevenness.

11.4 Operable voltage of LC101N

Operating conditions of LC101N are as follows:

• The minimum difference voltage between the IN pin and thr LED pin is higher than the ΔVDIF.
• The voltage of the IN pin is higher than 2.4V(min.) against the LO pin. One LED is added to the LED pin and setup resistor

as shown in Figure 11-1 in order to have enough voltage between the IN pin and the LO pin.

11.5 Overcurrent Protection (OCP)

The LC101N have the fold-back characteristics in overcurrent protection (OCP) as shown in Figure 13-2. The short circuit current does not return to completely 0 A, because start-up characteristics is considered. Thus, be careful to heat generation. When OCP is activated, the LED pin voltage decreases. Then, the difference voltage between input and output is increased, and the temperature of IC increases. In this case, Thermal shutdown might activate (refer to Section 11.6).

11.6 Thermal Shutdown (TSD)

LC101N has the Thermal Shutdown (TSD). The junction temperature of the IC chip, Tj, is detected. When Tj is increase to TSD = 130 °C (typ.), the drive current of the internal PNP transistor is limited. Since the minimum activation temperature of the TSD is 110 °C, Tj should be set less than 110 °C in thermal design.

TSD does not have hysteresis. When Tj decreases to TSD or less, the IC returns to normal operation automatically. When TSD is activated under the overcurrent condition, following condition is repeated and output voltage waveform, VLED, becomes intermittent oscillation (refer to Figure 13-4). Overcurrent condition −> VLED decreases −> ILED decreases −> junction temperature Tj decreases −> automatically restart −> Overcurrent condition….

• Notice of TSD The purpose of the TSD is the protection of IC from

temporary heat generation. TSD does not guarantee the operation including reliabilities under the continuous heat generation conditions, such as short circuit for a long time. Since the temperature of LC101N which is connected to the LED depends on the mounting location (distance) and the wiring method, TSD might be activated by the thermal of LEDs.

12. Design Notes

12.1 External Components

All components are required for matching to the condition of use.

12.1.1 LED current setup resistor, R1

Reference voltage of LC101N, VFB, controls the LED current, is 200 mV. The IC controls so that the VFB and both end voltage of setup resistor R1 is equal. Because the VFB is low voltage, the resistor should not be selected wirewound resistors to prevent malfunction in transient state including start/stop operation. In addition, lead of the resistor of through hole type should be short to reduce the back electromotive voltage by the parasitic inductance. R1 is recommended surface device, and should be as close to LC101N as possible. If the problem occurs at the open-short test of resistor, please considering the series-parallel connection of the resistor. R1 setup is as shown in Table 11-1.

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12.2 Pattern Layout

12.2.1 PCB Trace Layout and Component

Placement

• Setup resistance, R1, should be as close to the FB pin and the LO pin as possible as shown in Figure 12-1.
• The layout between the FB pin and the LED string should be avoided to parallel with switching trace. Noise is superimposed to the FB pin by induction, the LC101N might be malfunction.

FB pin and the LO pin.

Figure 12-1 Important locations of the pattern layout

12.2.2 Pattern Layout Example

Figure 12-2 shows the pattern layout example, and Table 12-1 shows this PCB information.

Table 12-1 PCB information of pattern layout example

(B) Bottom View

Figure 12-2 Pattern layout example

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Figure 12-3 Land pattern example (not to scale)

Figure 13-4 Thermal shutdown characteristic

Figure 13-2 Overcurrent characteristic

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14. Packing Specifications

14.1 Emboss and Carrier Tape Specification

The direction of tape drawer

Empty seal part

The direction of tape drawer

Figure 14-1 Emboss and carrier tape dimensions

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14.2 Reel Specifications

Figure 14-2 Reel dimensions

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15. Recommended Reflow Temperature Profile

Figure 15-1 Recommended reflow temperature profile

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IMPORTANT NOTES

• All data, illustrations, graphs, tables and any other information included in this document as to Sanken’s products listed herein (the “Sanken Products”) are current as of the date this document is issued. All contents in this document are subject to any change without notice due to improvement, etc. Please make sure that the contents set forth in this document reflect the latest revisions before use.
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