TLE7368

Detailed Internal Circuits Description

Data Sheet

24

Rev. 1.1, 2007-11-08

5.1.4

Charge Pump

The charge pump serves as support circuit for the Buck converter’s high side driver supply, the linear regulators

drive circuits for low drop operation and the internal device biasing blocks. In order to guarantee full device

operation at battery voltages as allow as even 4.5 V, the concept of a voltage tripler is chosen for the charge pump.

It operates at a switching frequency of typical 2 MHz utilizing three small external capacitors, two pumping caps

and one storage capacitor. The CCP circuit is equipped with a current limit function which avoids destruction in

case of a short of one of the external CCP capacitors. The charge pump’s output, CCP, is designed to supply the

circuitry described above, it should not be used as e.g. driver rail for external on board/PCB circuits.

5.1.5

Buck Converter Protection Circuits

Besides the circuits mandatory for the Buck converter operation additional protection circuits are foreseen which

the high side driver supply rail to ensure the device operates only with proper voltages present. The overvoltage

shutdown at the Buck converter output provides a safe high side shutdown for the case where the Buck control

loop becomes messed up due to non predictable circumstances. At overtemperatures the thermal shutdown circuit

disables the Buck converter until the device cools down to be enabled again.

5.2

Linear Regulators

The TLE7368 features three linear voltage regulator circuits, two fully integrated DMOS low drop voltage

regulators and one integrated linear control circuit to operate with an external NPN power stage.

Integrated linear regulator one (LDO1) offers a 5 V output and the second integrated linear regulator (LDO2) can

be configured with pin SEL_LDO2 either for 2.6 V or for 3.3 V. With SEL_LDO2 tied to GND 2.6 V will adjust at

the output of LDO2, SEL_LDO2 being connected to Q_LDO2 gives the 3.3 V option. The external regulator will

adjust its output to 1.5 V with the emitter of the NPN power stage directly connected to pin FB_EXT, by using a

voltage divider, higher output voltages can be achieved.

The regulators are designed for low drop operation and offer high output voltage accuracies to meet the needs of

current and next generation 32-bit microcontroller families. Additionally all regulators feature a short circuit

protection, i.e. the integrated regulators contain a output current limit function whereas the control circuit for the

external NPN power stage limits the maximum base current.

For low on chip power dissipation the input of LDO1 is internally directly connected to the Buck converter output

(FB/L_IN). LDO2’s input is on purpose externally accessible at IN_LDO2. This allows the insertion of a drop

element between the Buck converter output and IN_LDO2 to split the power dissipation and avoid high losses on

the TLE7368. Similar for the external NPN power stage regulator, the collector of the NPN can be either connected

directly to the Buck converter output or a drop element can be inserted in between to split power dissipation.

5.3

Voltage Tracking Regulators

For off board/off PCB supplies, i.e. sensors, two voltage tracking regulators are incorporated in the TLE7368. Their

outputs follow the output of the main 5 V regulator, Q_LDO1, within a tight tolerance of

±10 mV. The tracking

regulators are implemented with bipolar PNP power stages for improved ripple rejection to reduce emission when

lead off board. Both tracker outputs can withstand short circuits to GND and battery in a range of -5 V to +40 V.

When shorted to lower levels than the nominal output voltage level the current limit function prevents excessive

current draw.

1) Not shown in the schematic, Figure 3.