SRK2001 datasheet(15/22 Pages) STMICROELECTRONICS

15 / 22 page

DocID027367 Rev 3

15/22

SRK2001

Operation description

Figure 9. EN - PROG pin configurations

5.7.1

Automatic sleep mode function enabled

Only two resistors (REN - RPG) are used, connected from each of the two pins (EN-PROG)

and GND (see Figure 9): during the startup phase, an internal current generator IEN is

enabled, the sourcing current to the EN pin that sets the voltage across the external resistor

REN: by using a resistor value below or equal to 180 k, the voltage across this resistor

stays below an internal threshold and the controller enables automatic sleep mode function;

this configuration is internally stored and, afterward, the current generator value is

decreased to IEN_run.

At the same time, during the startup, a second current generator IPROG sourcing the current

to the PROG pin sets the voltage across the external resistor RPG: depending on this

voltage level, the sleep mode entering/exiting the conduction duty cycle is set, among those

contained into the two internal lookup tables (Table 6 and Table 7). After internal storing, the

current generator IPROG is disabled.

Either the lookup table is addressed depending on the value of the resistor REN. Table 6 and

Table 7 show the allowed duty cycle combinations depending on REN and RPG resistor

values (1% tolerance).

Table 6. Lookup table I: REN = 100 k

DOFF

DON

RPG

40%

80%

RPG = 0 

75%

RPG = 100 k

65%

RPG = 180 k

60%

RPG open

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