UM0970 datasheet(14/30 Pages) STMICROELECTRONICS

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Hardware and layout

UM0970

14/30

Doc ID 17693 Rev 2

3.6

Built-in IDD measurement circuit

The STM8L-DISCOVERY built-in IDD measurement circuit allows the consumption of the

STM8L152C6T6 to be measured and displayed on the LCD Glass while the MCU is in Run

or Low power saving modes.

●

JP1 in ON position: STM8L152C6T6 is powered through IDD measurement circuit

(default).

●

JP1 in OFF position: STM8L152C6T6 is powered directly by +3V3, IDD measurement

circuit is bypassed.

Note:

When jumper JP1 is removed the current consumption of the STM8L152C6T6 can be

measured by connecting an ammeter between jumper JP1 pin 1 and pin 2.

For IDD measurement by the MCU itself, the circuit below is implemented on the STM8L-

DISCOVERY. Solder bridges SB11, SB12 and SB14 must be closed and a jumper must be

plugged between JP1 pin 2 and pin 3.

Figure 10.

STM8L-DISCOVERY IDD measurement circuit

3.6.1

Run mode

In Run mode, IDD current is measured using the operational amplifier MAX9938FEUK+ (U4)

connected to the 2

Ω shunt resistor (R20). In this case IDD_CNT_EN remains high during

measurement, so R21 remains in short-circuit during the measurement because of

transistor T1 which remains ON permanently. The jumper JP1 must be connected between

pins 2 and 3 of JP1. The measurement range in this case can be up to 30 mA.

3.6.2

Low power mode

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

amplifier MAX9938FEUK+ (U4) connected to the 2K

Ωshunt resistor (R21), controlled by the

analogue switch STT5PF20V (T1). In this case the counter 74HC4060 (U3) enabled by

IDD_CNT_EN manages the measurement timing according to Figure 11. The measurement

range in this case can be up to 30 µA.

R19

47K

IDD_Measurement

IDD_CNT_EN

IDD_WAKEUP

74LX1G04CTR

I/O

O/I

GND

VCC

74H1G66STR

+3V3

R20

2(1%)

R21

2K(1%)

STT5PF20V

+3V3

Q12

Q13

Q14

GND

CLR

Q10

VCC

M74HC4060TTR

+3V3

R26

10K

R18

10K

C11

1uF

+3V3

VDD_MCU

JP1

C13

1nF

R22

15K

R23

30K

Oscillator frequency 30KHz

+3V3

R17

PF0

PE6

PC4

C12

100nF

MAX9938FEUK+

SB11

SB12

SB14

IDD

off

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