TLE7368

Application Information

Data Sheet

34

Rev. 1.1, 2007-11-08

This section intends to give hints for correct set up of the IC, i.e. to avoid misbehavior caused by the influence of

other PCB board circuits and shows also how to calculate external components, power loss, etc.

6.1

Choosing Components for the Buck Regulator

Stable operation of the Buck converter is ensured when choosing the external passive components according to

the characteristics given below:

•

Buck inductance: 18

•

Buck output capacitor:

C

•

ESR of Buck output capacitor: ESR_

C

6.2

Setting up LDO1, LDO2

The linear regulators LDO1 and LDO2 need to be connected to appropriate output capacitors in order to keep the

regulation loop stable and avoid oscillations. The essential parameters of the output capacitor are the minimum

capacitance and the equivalent series resistance (ESR). The required ranges for each output are specified in

Chapter 4.4 (Electrical Characteristics). Tantalum capacitors as well as multi layer ceramic capacitors are

suitable for LDO1 and LDO2.

6.3

Setting up of LDO3

LDO3 consists of an integrated regulator which needs to be equipped with an external power transistor (NPN-

Type). Suitable NPN power transistors types are e.g. KSH 200 from Fairchild semiconductor or NJD 2873T4 from

ON semiconductor. The most important parameters to be checked when choosing the external transistor are the

‘current gain bandwidth product’ (

f

Darlington type transistors should not be used. For stability of the regulation loop a multi layer ceramic capacitor

of min. 4.7

µF must be connected to the LDO3 output voltage (Emitter of the external power transistor). In order

to improve suppression load current steps an additional capacitor of tantalum type can be connected in parallel.

In case LDO3 voltage is not needed the external NPN transistor can be spared. For this configuration the pins

‘DRV_EXT’ and ‘FB_EXT’ should be directly connected to each other in order to ensure correct operation of

Reset 2. Also in this case a small ceramic capacitor of 220 nF connected from pin ‘FB_EXT’ to GND is

recommended in order to avoid oscillations of the regulation loop LDO3.

Table 1

LDO2 Output Voltage Configuration

No.

SEL_LDO2

Q_LDO2

1

GND

2.6 V

2

Q_LDO2

3.3 V