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september 2006 rev 2 1/12 12 AN2202 application note str73x microcontroller power management introduction this application note provides an overview of the str73x power management features and gives some guidelines for using the low power modes to minimize the power consumption of the microcontroller. example software is provided with this application note for implementing and showing the various low power modes. www.st.com
AN2202 2/12 contents 1 power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 power supply pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 internal regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.1 low power voltage regulator (lpvr) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 clock management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 clock configuration & power management . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 disabling peripherals clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 str73x low power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 low power mode characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 guidelines for entering/exiting low power modes . . . . . . . . . . . . . . . . . . . . . . 6 3.2.1 slow mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2.2 wfi mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.3 lpwfi mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.4 stop mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.5 halt mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4 example application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1 example hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2 example software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.3 power consumption measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
AN2202 1 power supply 3/12 1 power supply 1.1 power supply pins the following figure indicates the recommended configuration for the power supply pins: figure 1. str73x power supply pins v dd pin: is the 5v main power supply pin. v 18 pin: must be connected to a capacitor of at least 100nf (ceramic) in order to guarantee the stability of the 1.8v supply to the core. 1.2 internal regulators the following figure provides a schematic view of the power management block of the str73x. str73x v dd v 18 vss 100nf vss 5v av dd av ss v ss
1 power supply AN2202 4/12 figure 2. power management block note: * disconnected in lpwfi mode. main voltage regulator (mvr) in normal operation, the main voltage regulator (mvr) provides the 1.8v supply. the mvr can be switched off when entering a low power mode (refer to section 3 ) when the mvr is switched off, the low power voltage regulator (lpvr) can provide a power supply of about 1.8v (+/- 10%). note: 1 the mvr has a static power consumption of 3.97 ma typ at 25c. 2 when the mvr is switched off, the pll is automatically disabled (pll off) and the maximum allowed operating frequency is 2 mhz, this is due to the limitation imposed by the lpvr which is not able to generate sufficient current to operate in run mode. 1.2.1 low power voltage regulator (lpvr) the low power voltage regulator (lpvr) is used when the mcu is in lo w-power mode and the main voltage regulator has been switched off. it has a different design from the main voltage regulator and generates a stabilized and thermally-compensated voltage in the range of 1.8v (+/- 10%), its output current is not generally sufficient for the device to run in normal operation. av dd av ss v 18 a/d converter memory and i/os v18 note* main voltage regulator v dd low power voltage regulator core and peripherals peripherals active in lpwfi mode v18
AN2202 2 clock management 5/12 2 clock management the following figure provides an overview of the clock management block of the str73x: figure 3. clock management block legend: f mclk = to cpu and peripherals f clk1 = from cmu, to prccu f clk2 = before pll 2.1 clock configuration & power management different clock configurations are provided by the str73x mcu offering the means to optimize the power consumption in the device, the main features are: individual peripheral clock disabling. up to three low power system clocks: clk2, clk2/16 and the pll free running mode clock (refer to the prccu section in the str73x reference manual for details on the pll free running mode). 2.2 disabling peripherals clocks the peripheral clock managing registers (pcgr0 and pcgr1 of the configuration registers) allows each module clock of the device to be switched on/off individually. refer to the configuration registers section in the str73x reference manual. note: 1 pll is automatically disabled when: - the main voltage regu lator (mvr) is stopped - entering lpwfi, stop or halt low power modes - when prccu_pllcr dx[2:0] bits are set to ?111? and freen bit is reset 2 when not using the rc clock, you can disable it by settin g bit rchse and/or rcss in the pcu_ctrl register. 1/2 pll xtal1 xtal2 1/16 prescaler prccu main oscillator rc oscillator back up cmu wake up timer f osc f rc v bias f clk1 f clk2 f mclk f ext
3 str73x low power modes AN2202 6/12 3 str73x low power modes 3.1 low power mode characteristics the str73x low power modes are summarized in the following table: table 1. str73x low power modes note: 1 refer to figure 3 for the definition of the various clocks (mclk, clk1, clk2, clk2/16, rc). 3.2 guidelines for entering /exiting low power modes 3.2.1 slow mode to enter slow mode, mclk must be configured as clk2 or clk2/16. when using these clock settings, the pll can be disabled by writing ?111? in the dx[2:0] bits in the prccu_pllcr register. table 2. slow mode selection note: 1 csu_cksel is bit 0 in register prccu_cfr. 2 ck2_16 is bit 3 in register prccu_cfr power mode description slow - pll off and mclk 1) = clk2 or clk2/16 - free running pll wait for interrupt (wfi) - core stopped (mclk off) - wake-up by interrupts acknowledged by the interrupt controller (eic) - mcu state retained (context restored after wakeup) low power wfi (lpwfi) - core stopped (mclk off) - peripherals running at slow clock: clk2/16 - wake-up by interrupts acknowledged by the eic - mcu state retained stop - core and peripherals stopped (mclk off) - wake-up by the configured external wake-up lines - mcu state retained halt - oscillators stopped - wake up is only possible by means of external reset (h/w pin) or lvd reset (power-on) as the rc oscillator is off mclk csu_cksel 1) ck2_16 2) freen 3) clk2 0 1 0 clk2/16 x 0 0 free running pll 1 1 1
AN2202 3 str73x low power modes 7/12 3 freen is bit 7 in register prccu_ pllcr, in the same register th e dx(2:0) must be all sets in order to provide the pll slow frequency. 3.2.2 wfi mode to enter wfi mode, you must clear t he wfi bit in the prccu_smr register. to wakeup from wfi mode an interrupt request must be acknowledged by the eic. 3.2.3 lpwfi mode to enter lpwfi mode you have to: 1. select the clock which will be used by perip herals during lpwfi: rc or external oscillator with the cmu (cksel0 bit in the cmu_ctrl regi ster), this clock can be set as running low (with rcfr bit in cmu_ctrl register) 2. during the lpwfi, the clock used will be divided by 16: clk2/16 (wfi_cksel bit of the prccu_ccr register) 3. select lpwfi mode by setting the lpowfi bit in the prccu_ccr register. 4. write 0 in the wfi bit of the prccu_smr register to enter lpwfi mode like wfi mode, to wakeup from lpwfi mode an interrupt request must be acknowledged by the eic. to further reduce mcu power consumption in lpwfi mode you can: stop the main voltage regulator (mvr) by setting bit vrlpw in the prccu_vrctr register. in lpwfi, the flash module should enter power down mode by setting the lps bit of flash cr0 register status. note: 1 after exit from lpwfi mode, the flash and the main voltage regulator are re-enabled automatically if they were switched off during the low power mode. 2 after wakeup, the original mclk clock configuration must be restored by software. 3.2.4 stop mode to enter stop mode you have to: 1. configure at least one external wake-up line or wut to wake-up the mcu from stop mode. (refer to the wiu & wut section in the str73x reference manual) 2. reset the stop bit in register wiu_ ctrl and the stop_i bit in the prccu_cfr register. 3. to enter stop mode, write the sequence 1, 0, 1 to the stop bit in the wiu_ctrl register. 4. in order to avoid executing any valid instructions after a stop bit setting sequence and before entering stop mode, it is mandatory to execute a few (at least 6) dummy instructions after the stop bit setting sequence. 5. to be sure that stop mode was really entered, immediately after the end of the stop bit setting sequence (including th e dummy instructions), poll th e prccu stop_i flag bit and the stop bit (wiu_ctrl register). if the stop bit setting sequence has been correctly executed, these bits must be stop_i = 1 and stop = 0. if it is not the case you must restart all the sequence from the beginning. 6. when exiting stop mode, clear the pending wake up interrupt line (wiu_pr register).
3 str73x low power modes AN2202 8/12 7. on wake-up from stop mode, the cmu aut omatically selects th e 2mhz rc-oscillator clock as input clock to the prccu. to further reduce power consumption during stop mode, it is possible to: disable the main voltage regulator by writ ing ?1? in bit vrlpw in the prccu_vrctr register. minimize the low power voltage regulator current capability by setting the bit 0 and 1 of the system configuration register 1 (lpvrcc(1:0)). note: after exit from stop mode, the flash and the main voltage regulator are re-enabled automatically if they were switched off during the stop mode 3.2.5 halt mode the halt sequence is initia ted with the following procedure: set the en_halt bit in the prccu_smr and clear the sresen bit in the prccu_ccr then set the halt bit in the prccu_ccr. caution: wake-up from halt mode is only possible by means of an external or lvd reset. note: minimize the low power voltage regulator curr ent capability by setting the bit 0 and 1 of the system configuration re gister 1 (lpvrcc(1:0)).
AN2202 4 example application 9/12 4 example application 4.1 example hardware figure 4 shows an example schematic for using the str73x power management features. figure 4. example application schematic note: 1 wup6 is configured as an external interrupt pin, it is used to wake up the mcu from wfi, lpwfi or stop mode. 2 p4.6 is used to indicate that the core is running (gpio toggling) during run/slow modes. 3 p5.8 is used to enter halt or slow modes. it is used also to exit from slow_rc mode. 4.2 example software a program is provided with this application note for using the different low power modes, it includes the following source files: str73x v dd v 18 v dd1 =5v p5.8 p4.6 led1 xtal1 xtal2 15pf 15pf 4mhz nrstin vbias wup6 100nf a 10k 1k 1.3m 10k 100nf 100nf v dd2 =5v v dd2 =5v 100 v dd2 =5v 10nf v dd2 =5v
4 example application AN2202 10/12 table 3. software files the following routines are implemented in the main.c file: table 4. low power mode routines note: to select a low power mode, you have to uncomment the corresponding define code ?#define xxx_mode and rebuild the main.c file. 4.3 power consumption measurements all consumption measurements are listed in the str73x datasheet. file description main.c example software for using different low power modes 73x_it.c interrupt service routines modes mode configuration/ options during the selected low power mode run_mode - rc oscillator off, rtc on, tim3 on and flash on. run_allon_mode - all peripheral on. slow_mode - clk2, clk2_16 or free running pll selectable slow_rc_mode - clk (clk2 with div2 disabled) wfi_mode - value of mclk can be modified lpwfi_mode - main voltage regulator (mvr) stopped (software selectable) - flash in power down or in low power (software selectable) - wup6 pin configured as external rising edge interrupt lpwfi_rc_mode - rc running high clock is used (software selectable) - main voltage regulator (mvr) stopped (software selectable) - flash in power down or in low power (software selectable) - wup6 pin configured as external rising edge interrupt stop_mode - flash in power down - main voltage regulator (mvr) stopped (software selectable) - wakeup by wup6 pin configured as rising edge wakeup stop_wut_mode - flash in power down - main voltage regulator (mvr) stopped (software selectable) - wakeup by the wut configured as rising edge. wakeup after 10 second delay halt_mode - device halted.
AN2202 5 revision history 11/12 5 revision history date revision changes 05-jan-2006 1 initial release 12-09-2006 2 figure 4 on page 9 : example application schematic updated. section 3.2.1 on page 6 : slow mode updated. section 3.2.4 on page 7 : stop mode updated. table 4 on page 10 : low power mode routines updated.
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