 English |
|
|
|
|
|
|
|
| LM3409MY-NOPB Datasheet, PDF (10/43 Pages) Texas Instruments – PFET Buck Controller for High Power LED Drivers | |||
| |||
| ◁ |
LM3409, LM3409HV, LM3409-Q1
SNVS602J â MARCH 2009 â REVISED MAY 2013
LM3409/09HV
tON
ENDS
5R
www.ti.com
R
- VCST +
CSP
CSN
R
VIN
R SNS
+
VSNS
-
IT
5V
PGATE
Q1
5#A
L1 IL
LED +
IADJ
1.24 V
GND
+
VADJ
-
D1
R EXT
Optional
LED-
Figure 22. Peak Current Control Circuit
There are three different methods to set the current sense threshold (VCST) using the multi-function IADJ pin:
1. IADJ pin left open: 5µA internal current source biases the Zener diode and clamps the IADJ pin voltage
(VADJ) at 1.24V causing the maximum threshold voltage:
VCST =
VADJ
5xR
xR=
VADJ
5
=
1.24V
5
=
248
mV
(2)
2. External voltage (VADJ) of 0V to 1.24V: Apply to the IADJ pin to adjust VCST from 0V to 248mV. If the VADJ
voltage is adjustable, analog dimming can be achieved.
3. External resistor (REXT) placed from IADJ pin to ground: 5µA current source sets the VADJ voltage and
corresponding threshold voltage:
VCST
=
VADJ
5
=
5#A x REXT
5
= 1#A x REXT
(3)
Controlled Off-Time
Once Q1 is turned off, it remains off for a constant time (tOFF) which is preset by an external resistor (ROFF), an
external capacitor (COFF), and the output voltage (VO) as shown in Figure 23. Since ILED is tightly regulated, VO
will remain nearly constant over widely varying input voltage and temperature yielding a nearly constant tOFF.
10
Submit Documentation Feedback
Copyright © 2009â2013, Texas Instruments Incorporated
Product Folder Links: LM3409 LM3409HV LM3409-Q1
|
▷ |
German
Russian
Spanish
Italian
Polish
Chinese
Japanese
Korean
French
Portuguese