L9805 datasheet(26/103 Pages) STMICROELECTRONICS

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L9805

4 VOLTAGE REGULATOR

4.1 Introduction

The on chip voltage regulator provides two regu-

lated voltage, nominally 5V both. VCC supplies

ADC and the analog periphery and VDD supplies

the microcontroller and logic parts. These voltage

are available at pins VDD and VCC to supply ex-

ternal components and connects a capacitors to

optimize EMI performance. A pre-regulator circuit

allows to connect external tantalum capacitors to a

lower (10V) voltage (VB2 pin).

4.1.1 Functional Description

The main supply voltage is taken from VB1 pin. A

voltage pre-regulator provides the regulated volt-

age on pin VB2. VB2 is the supply for the digital

and analog regulators. The block diagram shows

the connections between the regulators and the

external pins.

In order to prevent negative spikes on the battery

line to propagate on the internal supply generating

spurious reset, a series diode supply VB1 pin is

recommended.

Figure 14. Voltage regulation block diagram

4.2 Digital Section Power Supply

The digital supply voltage VDD is available at pin

number 42 and 9. The digital ground GND is avail-

able at pin number 43 and 12.

Pin 42 and 43 are the actual voltage regulator out-

put and external loads must be supply by these

pin. The 100nF compensation capacitor should be

connected as close as possible to pin 42 and 43.

Pin number 9 and 12 provide an external access to

the internal oscillator supply. Resonator’s capaci-

tors should be grounded on pin 12.

ADC

PRE-REGULATOR

VB1

VB2

force

ANALOG

VOLTAGE

REGULATOR

sense

VCC

AGND

DIGITAL

VOLTAGE

REGULATOR

VDD(42)

GND(43)

Battery

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