UM1574 datasheet(29/48 Pages) STMICROELECTRONICS

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UM1574

Hardware and layout

Doc ID 023645 Rev 1

29/48

Figure 16.

STM8AL board IDD measurement circuit

●

Run mode

In Run mode, IDD current is measured using the operational amplifier MAX9938FEUK+ (U8)

connected to the 2  shunt resistor (R23). In this case IDD_CNT_EN remains high during

measurement, so R24 remains in short-circuit during the measurement because of switch

U5 which remains ON permanently. The jumper JP2 must be connected between pins 2 and

3 of JP2. The measurement range in this case can be up to 30 mA.

●

Low power mode

In Low power modes (Halt or Active halt), IDD current is measured using the operational

amplifier MAX9938FEUK+ (U8) connected to the 2 K shunt resistor (R24), controlled by

the switch STS4DPF20L (U5). In this case the counter 74HC4060 (U7) enabled by

IDD_CNT_EN manages the measurement timing according to Figure 17. The measurement

range in this case can be up to 30 µA.

●

Low power mode IDD measurement principle

The principle used to measure a current when the STM8AL3L68T is in Low power mode is:

Configure ADC to measure voltage on the IDD_Measurement pin.

Configure PE6 to serve as wakeup pin.

Enter Low power mode after setting IDD_CNT_EN (PC4) signal low.

IDD_WAKEUP rising edge wakes up the MCU after around 300 ms.

Start ADC conversion as soon as possible after wakeup in order to measure the

voltage corresponding to Low power mode on capacitor C14.

Reset the counter by programming IDD_CNT_EN high (in less than 70 ms after the

wakeup) to avoid the R24 2 K resistor being connected later in Run mode.

R28

47K

74LX1G04CTR

I/O

O/I

GND

VCC

74H1G66STR

R23

2(1%)

R24

2K(1%)

Q12

Q13

Q14

GND

CLR

Q10

VCC

R26

10K

R25

10K

C14

1uF

JP2

C16

1nF

R29

15K

R27

30K

Oscillator frequency 30 KHz

R22

C15

100nF

SB6

SB8

SB7

IDD Measure

MAX9938FEUK+

STS4 DPF20L

IDD_Measurement

DD_CNT_EN

IDD_WAKEUP

PF0

PE6

PC4

3V3

MS31059V1

M74HC4060TTR

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