EVAL5987 STMicroelectronics, EVAL5987 Datasheet - Page 19

BOARD EVALUATION FOR L5987

EVAL5987

Manufacturer Part Number
EVAL5987
Description
BOARD EVALUATION FOR L5987
Manufacturer
STMicroelectronics
Type
DC/DC Switching Converters, Regulators & Controllersr
Datasheets

Specifications of EVAL5987

Main Purpose
DC/DC, Step Down
Outputs And Type
1, Non-Isolated
Voltage - Output
1.8V
Current - Output
3A
Voltage - Input
2.9 ~ 18V
Regulator Topology
Buck
Board Type
Fully Populated
Utilized Ic / Part
L5987
Input Voltage
2.9 to 18 V
Output Voltage
1.8 V
Operating Supply Voltage
2.9 to 18 V
Product
Power Management Modules
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Frequency - Switching
-
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
For Use With/related Products
L5987
Other names
497-8369

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
EVAL5987
Manufacturer:
ST
0
Part Number:
EVAL5987A
Manufacturer:
ST
0
L5987
6.3
Output capacitor selection
The current in the capacitor has a triangular waveform which generates a voltage ripple
across it. This ripple is due to the capacitive component (charge or discharge of the output
capacitor) and the resistive component (due to the voltage drop across its ESR). So the
output capacitor has to be selected in order to have a voltage ripple compliant with the
application requirements.
The amount of the voltage ripple can be calculated starting from the current ripple obtained
by the inductor selection.
Equation 13
Usually the resistive component of the ripple is much higher than the capacitive one, if the
output capacitor adopted is not a multi layer ceramic capacitor (MLCC) with very low ESR
value.
The output capacitor is important also for loop stability: it fixes the double LC filter pole and
the zero due to its ESR. In
system stability.
For example with V
order to have a ΔV
are needed and the ESR effect on the output voltage ripple can be neglected. In case of not
negligible ESR (electrolytic or tantalum capacitors), the capacitor is chosen taking into
account its ESR value. So in case of 330 μF with ESR = 30 mΩ, the resistive component of
the drop dominates and the voltage ripple is 27 mV.
The output capacitor is also important to sustain the output voltage when a load transient
with high slew rate is required by the load. When the load transient slew rate exceeds the
system bandwidth the output capacitor provides the current to the load. So if the high slew
rate load transient is required by the application the output capacitor and system bandwidth
have to be chosen in order to sustain the load transient.
In the table below some capacitor series are listed.
Table 8.
Manufacturer
Panasonic
MURATA
SANYO
TDK
Output capacitors
OUT
OUT
TPA/B/C
= 0.01·V
GRM32
GRM31
EEFCD
= 3.3 V, V
Series
C3225
ECJ
Chapter
ΔV
Doc ID 14972 Rev 3
OUT
OUT
IN
, if the multi layer ceramic capacitor are adopted, 13 μF
=
= 12 V, ΔI
6.4, it will be illustrated how to consider its effect in the
ESR ΔI
Cap value (μF)
100 to 470
22 to 100
22 to 100
10 to 47
10 to 22
10 to 68
MAX
L
= 0.9 A (resulting by the inductor value), in
+
------------------------------------ -
8 C
ΔI
OUT
Rated voltage (V)
MAX
f
6.3 to 25
6.3 to 25
SW
4 to 16
6.3
6.3
6.3
Application information
ESR (mΩ)
15 to 55
40 to 80
< 5
< 5
< 5
< 5
19/41

Related parts for EVAL5987