TLD5085EJ_15 Datasheet, PDF (14/19 Pages) Infineon Technologies AG – 1.8A DC/DC Step-Down Converter

Infineon® LITIX™ Power
TLD5085EJ
Application Information
Confidential
8
Application Information
Note: The following information is given as a hint for the implementation of the device only and shall not be
regarded as a description or warranty of a certain functionality, condition or quality of the device.
8.1
Frequency Compensation
The stability of the output voltage can be achieved with a simple RC connected between pin COMP and GND.
The standard configuration using the switching frequency of the internal oscillator is a ceramic capacitor
CCOMP = 22nF and RCOMP = 22kW. By slight modifications to the compensation network the stability can be
optimized for different types of buck capacitors (ceramic or tantalum).
The compensation network is essential for the control loop stability. Leaving pin COMP open might lead to an
instable operation.
8.2
Compensating a Tantalum Buck Capacitor C_BU1
The TLD5085EJ control loop is optimized for ceramic buck capacitors CBU. In order to maintain stability also
for tantalum capacitors with ESR up to 300mΩ, an additional compensation capacitance C_COMP2 at pin COMP
to GND is required. Its value is calculated as follows:
C_{COMP 2=}
C _BU
⋅ ESR (C_BU
R_COMP
)
(8.1)
whereby C_COMP2 needs to stay below 5nF.
C_COMP2
COMP
3
C_COMP
R_COMP
Application _C-COMP2.vsd
TLD5085
2
GND
Figure 8-1 High-ESR Buck Capacitor Compensation
8.3
Freewheeling Diode
In order to minimize losses and for fast recovery, a Schottky freewheeling diode is required. Disconnecting the
freewheeling diode during operation might lead to destruction of the IC.
Data Sheet
16
Revision 1.1
2015-03-10