L7986TA STMicroelectronics, L7986TA Datasheet - Page 16

• Manufacturer Part Number: L7986TA
• Description: 3A step-down switching regulator
• Manufacturer: STMicroelectronics

Specifications of L7986TA

• Low Dropout Operation: 100% duty cycle

Application informations
6.2
16/43
Given the physical dimension, ceramic capacitors can meet well the requirements of the
input filter sustaining an higher input RMS current than electrolytic / tantalum types. In this
case the equation of C
Equation 10
neglecting the small ESR of ceramic capacitors.
Considering η=1, this function has its maximum in D=0.5, thus, given the maximum peak to
peak input voltage (V
Equation 11
Typically C
V
In
Table 6.
A ceramic bypass capacitor, as close to the VCC and GND pins as possible, so that
additional parasitic ESR and ESL are minimized, is suggested in order to prevent instability
on the output voltage due to noise. The value of the bypass capacitor can go from 100 nF to
1 µF.
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 continuous current mode (CCM), the inductance value can be calculated by the
following equation:
INMAX
Figure 6
Manufacture
Taiyo Yuden
Murata
IN
some Multi layer ceramic capacitors suitable for this device are reported
Input MLCC capacitors
is dimensioned to keep the maximum peak-peak voltage in the order of 1% of
PP_MAX
IN
UMK325BJ106MM-T
GMK325BJ106MN-T
as a function of the target V
GRM32ER71H475K
C
IN
), the minimum input capacitor (C
Doc ID 022098 Rev 1
=
Series
-------------------------- -
V
C
PP
IN_MIN
I
⋅
O
F
SW
=
⋅
----------------------------------------------- -
2 V
⎛
⎝
⋅
1 D
–
PP_MAX
--- -
η
⎞ D
⎠
I
Cap value (μF)
O
⋅
PP
+
⋅
F
D
--- -
η
4.7
can be written as follows:
10
10
SW
⋅
(
1 D
–
IN_MIN
)
) value is:
Rated voltage (V)
35
50
50
L7986TA