Datasheet

LM3150
SNVS561D –SEPTEMBER 2008–REVISED MARCH 2011 www.ti.com
Table 1. Inductor Selection Table (continued)
Inductor Designator Inductance Current Part Name Vendor
(µH) (A)
L26 15 12-15
L27 10 12-15 SER2814L-103KL COILCRAFT
L28 6.8 12-15 7447709006 WURTH
L29 4.7 12-15 7447709004 WURTH
L30 3.3 12-15
L31 2.2 12-15
L32 1.5 12-15 MLC1245-152 COILCRAFT
L33 1 12-15
L34 0.68 12-15 DO3316H-681 COILCRAFT
L35 0.47 12-15
L36 0.33 12-15 DR73-R33-R COOPER
L37 22 15-
L38 15 15- SER2817H-153KL COILCRAFT
L39 10 15- SER2814H-103KL COILCRAFT
L40 6.8 15-
L41 4.7 15- SER2013-472ML COILCRAFT
L42 3.3 15- SER2013-362L COILCRAFT
L43 2.2 15-
L44 1.5 15- HA3778–AL COILCRAFT
L45 1 15- B82477-G4102-M EPCOS
L46 0.68 15-
L47 0.47 15-
L48 0.33 15-
5. Determine Output Capacitance
Typical hysteretic COT converters similar to the LM3150 require a certain amount of ripple that is generated
across the ESR of the output capacitor and fed back to the error comparator. Emulated Ripple Mode control built
into the LM3150 will recreate a similar ripple signal and thus the requirement for output capacitor ESR will
decrease compared to a typical Hysteretic COT converter. The emulated ripple is generated by sensing the
voltage signal across the low-side FET and is then compared to the FB voltage at the error comparator input to
determine when to initiate the next on-time period.
C
Omin
= 70 / (f
s
2
x L) (17)
The maximum ESR allowed to prevent over-voltage protection during normal operation is:
ESR
max
= (80 mV x L x A
f
) / ET
min
(18)
ET
min
is calculated using V
IN-MIN
A
f
= V
OUT
/ 0.6 if there is no feed-forward capacitor used
A
f
= 1 if there is a feed-forward capacitor used
The minimum ESR must meet both of the following criteria:
ESR
min
≥ (15 mV x L x A
f
) / ET
max
(19)
ESR
min
≥ [ ET
max
/ (V
IN
- V
OUT
) ] x (A
f
/ C
O
) (20)
ET
max
is calculated using V
IN-MAX
.
Any additional parallel capacitors should be chosen so that their effective impedance will not negatively attenuate
the output ripple voltage.
6. Determine The Use of Feed-Forward Capacitor
Certain applications may require a feed-forward capacitor for improved stability and easier selection of available
output capacitance. Use the following equation to calculate the value of C
ff
.
14 Submit Documentation Feedback Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Links: LM3150