AN2846 datasheet(13/35 Pages) STMICROELECTRONICS

13 / 35 page

AN2846

Application guidelines

Doc ID 15130 Rev 1

13/35

Figure 17.

Regulator output voltage

Figure 18 shows the schematic diagram of a solution for applications where greater current

is needed. The bypass transistor allows extra current while maintaining a 5 V regulated

voltage (see Figure 19).

The proposed circuit allows a 25 mA current load capability with a VDD regulation <2%. An

additional input protection device, like SMAJ30A, is needed to comply with voltage surges

because RC has to be reduced to limit the voltage drop across it.

The dissipated power in the bypass transistor PZT2N2907A is 550 mW.

Components used:

●

PZT2N2907A (SOT223 with 1 cm2 copper area)

●

RC = 330 Ω (1/8 W), RE = 51 Ω (1/8 W)

1.4

SPI functional description

Three registers (refer to Figure 1) are used to transfer input data and control data to the

16-bit data frame. The data frames are transmitted through four interface signals: /CS, SCK,

MOSI, and MISO.

4.5

4.6

4.7

4.8

4.9

5.0

5.1

-3%

9.0

(V)

(mA)

versus I

Figure 18.

VDD booster schematic

Figure 19.

Load regulation with VDD booster

2N2907A

IDD

VDD

IRC

SMAJ30A

SCLT3

IN1

IN2

IN3

IN4

VDD

LED2

LED3

LED1

RREF

VCS

0.00

5.00

10.00

15.00

20.00

25.00

4.800

4.850

4.900

4.950

5.000

5.050

5.100

0.00

5.00

10.00

15.00

20.00

25.00

(mA)

(V)

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