LM3492 datasheet(13/24 Pages) TI

13 / 24 page

LM3492, LM3492Q

www.ti.com

SNVS656C – SEPTEMBER 2010 – REVISED MAY 2013

Output Voltage Feedback

The output voltage is fed back to the FB pin through a feedback circuit consists of RFB1, RFB2, and CFB as shown

in Figure 21. The value of CFB is recommended to be 10 pF in order to help feed the AC component of the output

voltage back. The DC component of the output voltage is fed back by RFB1 and RFB2. The voltage of the FB pin

VFB can be adjusted from 1.05V to 2.5V by DHC. The maximum output voltage of the boost converter VOUT(MAX)

VOUT(MAX) = 2.5V (1 + RFB1/ RFB2)

(3)

Under DHC, the output voltage should be maintained at a nominal voltage but not the maximum. The nominal

output voltage (VOUT(NOM)) is

VOUT(NOM) = max (VLED,n + VIOUT,n), n = 1, 2

where

•

VLED,n is the forward voltage of LED string n

•

VIOUT,n is the voltage of the IOUTn pin

•

where n is 1, 2 for channels 1, 2 of the current regulator)

(4)

The minimum value of VIOUT,n is about 5Ω x ILED. It is recommended that the nominal voltage of the FB pin

(VFB(NOM)) is between 1.05V to 2V. Hence, the equation relating VOUT(MAX), VOUT(NOM), and VFB(NOM) is as follows:

VOUT(MAX) = VOUT(NOM) x 2.5V / VFB(NOM)

(5)

Figure 21. Output Voltage Feedback Circuit

Bi-Directional Communication Pin

The COMM pin of the LM3492 is an open-drain bi-directional I/O pin for interfacing with an external MCU for the

following functions: power-good indication, over-temperature indication, IOUT over- and under-voltage

indications, switching frequency tuning, and channel 1 disabling. Except the power good indication and the over-

temperature alert, all data flow through the COMM pin is serial and is latched by the falling edge of the signal

applying to the DIM1 pin, even when channel 1 of the current regulator is disabled. If the DIM1 pin stays only low

or only high, either by an external circuit or letting it open and pull low internally, data flow will not happen.

Figure 22 and Figure 23 show a timing diagram of reading and writing a bit from and to the LM3492 through the

COMM pin.

The COMM pin should be pull-up by an MCU I/O pin which has pull-up capability or an external resistor RCOMM to

the VCC pin. Otherwise, the voltage of the COMM pin will remain at zero. The rise time of the output signal of the

COMM pin depends on the pull-up power. If the rise time is long (RCOMM is too large or pull-up power from the

connecting MCU I/O pin is too weak), data may be ready after a longer duration after the falling edge. In this

case, a longer delay between the falling edge latching and the (input or output) bit is required.

Submit Documentation Feedback

Product Folder Links: LM3492 LM3492Q

LM3492 Datasheet(PDF) 13 Page - Texas Instruments

LM3492 Datasheet(HTML) 13 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL