L5985TR STMicroelectronics, L5985TR Datasheet - Page 15

IC REG SW 2A STEP DOWN 8-VFQFPN

L5985TR

Manufacturer Part Number
L5985TR
Description
IC REG SW 2A STEP DOWN 8-VFQFPN
Manufacturer
STMicroelectronics
Type
Step-Down (Buck)r
Datasheet

Specifications of L5985TR

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
0.6 ~ 18 V
Current - Output
2A
Frequency - Switching
250kHz ~ 1MHz
Voltage - Input
2.9 ~ 18 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
8-VFQFN, 8-VFQFPN
Power - Output
1.5W
Output Voltage
3 V
Output Current
2 A
Input Voltage
2.9 V to 18 V
Switching Frequency
220 KHz to 275 KHz
Operating Temperature Range
- 40 C to + 150 C
Mounting Style
SMD/SMT
Duty Cycle (max)
100 %
For Use With
497-6387 - BOARD EVAL FOR L5985
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Other names
497-6861-2
L5985TR

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L5985
5.2
Inductor selection
The inductance value fixes the current ripple flowing through the output capacitor. So the
minimum inductance value in order to have the expected current ripple has to be selected.
The rule to fix the current ripple value is to have a ripple at 20%-40% of the output current. In
the continuos current mode (CCM), the inductance value can be calculated by the following
equation:
Equation 6
Where T
time of the external diode (in CCM, F
fixed Vout, is obtained at maximum T
to calculate minimum duty). So fixing ΔI
minimum inductance value can be calculated:
Equation 7
where F
For example for V
inductance value to have ΔI
The peak current through the inductor is given by:
Equation 8
So if the inductor value decreases, the peak current (that has to be lower than the current
limit of the device) increases. The higher is the inductor value, the higher is the average
output current that can be delivered, without reaching the current limit.
In the table below some inductor part numbers are listed.
Table 7.
Manufacturer
Coiltronics
Coilcraft
SW
ON
Wurth
is the conduction time of the internal high side switch and T
is the switching frequency 1/(T
Inductors
OUT
= 3.3 V, V
ΔI
L
L
= 30% of I
=
PD type S
MSS1038
MSS7341
Doc ID 13006 Rev 5
UP2.8B
Series
V
----------------------------- - T
IN
L
CD1
IN
MIN
= 12 V, I
L
OFF
V
SW
=
OUT
I
L PK
O
L
,
V
--------------------------- -
= 1 / (T
that is at minimum duty cycle (see previous section
= 20% to 40% of the maximum output current, the
OUT
is about 18 μH.
ΔI
ON
O
MAX
=
= 2 A and F
ON
+
+ T
I
O
ON
V
=
Inductor value (μH)
+
F
OFF
ΔI
------- -
V
--------------------------- - T
+ T
2
1 D
---------------------- -
OUT
L
).
3.3 to 6.8
3.3 to 6.2
F
4.7 to 10
OFF
15 to 18
15 to 22
SW
L
+
MIN
SW
)). The maximum current ripple, at
V
F
= 250 kHz the minimum
OFF
Application information
Saturation current (A)
OFF
is the conduction
2.75 to 4.2
3.2 to 3.6
2.5 to 3.5
2.7 to 3.9
2.9 to 3.6
15/37

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