'IL =

where

VIN u

VOUT - VIN

(

)

2

u fSW u L u VOUT

VOUT

VIN

+ 'IL

u

ILOAD

K

IPEAK =

LM3565

www.ti.com

SNVS957 – JANUARY 2013

Input Low Voltage Flag (ILV)

The LM3565 has an Input Low Voltage (ILV) detection mechanism that sets the ILV flag (bit1 in address 0x08)

when this feature is enabled (LVEN = 1, bit6 in address 0x04) and the input voltage is below the threshold set in

the Low Voltage Control Register (LVL2-LVL0 in address 0x04). The input voltage is only monitored before the

start of a flash event. This is a reporting flag bit and not a fault bit. The ILV flag bit does not halt or reset the

LM3565.

TX-Mask Flag (TXM)

The LM3565 has a Transmit Interrupt flag bit (TXM, bit 3 in address 0x08) that gets set if the TX-Mask feature is

enabled (TXEN = 1, bit7 in address 0x03) and if the TX-Mask pin is high, indicating a TX-Mask event. This is a

reporting flag bit and not a fault bit. The TXM flag bit does not halt or reset the LM3565.

Table 9. Application Circuit Components List

Component

Manufacturer

Value

Part Number

Current/Voltage Rating (Resistance)

L

Toko

1µH

1239AS-H-1R0N

ISAT = 3A (59 mΩ)

COUT1, COUT2

Murata

10 µF

GRM21BR61C106KE15

16 V

CIN1

Murata

10 µF

GRM188R60J106ME47

6.3 V

CIN2

Murata

0.1 µF

GRM155R71C104KA88

16 V

Inductor Current Limit

To prevent damage to the LM3565's inductor and to limit the power drawn by the LM3565 during a flash event,

an Inductor Current Limit circuit is present. The LM3565 monitors the current through the inductor during the

charge phase of the boost cycle. In the event that the inductor current reaches the current limit, the NFET of the

converter will terminate the charge phase for that cycle. The process will repeat itself until the flash event has

ended or until the input voltage increases to the point where the peak current is no longer reached. Hitting the

peak inductor current limit will not disable the part. It will however limit the output power delivery to the LEDs.

The inductor current limit can be set to 2.3A, 2.6A (default), 2.9A or 3.3A depending on the values of the ICL1

and ICL0 bits in the TX-Masking Register (Address 0x03). The peak inductor current limit value can be used to

help size the inductor to the appropriate saturation current level. For more information on inductor sizing, refer to

the INDUCTOR SELECTION section of this datasheet.

Inductor Selection

The LM3565 is designed to use a 1µH inductor. When the device is boosting (VOUT > VIN) the inductor is one of

the biggest sources of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest possible

series resistance is important. Additionally, the saturation rating of the inductor should be greater than the

maximum operating peak current of the LM3565. This prevents excess efficiency loss that can occur with

inductors that operate in saturation and prevents over-heating of the inductor and possible damage. For proper

inductor operation and circuit performance ensure that the inductor saturation and the peak current limit setting of

the LM3565 (2.3A, 2.6A (default), 2.9A or 3.3A) is greater than IPEAK. IPEAK can be calculated by:

Copyright © 2013, Texas Instruments Incorporated

29

Product Folder Links: LM3565