Nokia RM-42 Service Manual page 433

RM-42
System Module
• LDO
• camera LDO
• backlight SMPS
All the above are powered by the main battery voltage.
Battery voltage is also used on the RF side for power amplifiers (GSM PA & WCDMA PA) and for RF ASICs Hinku
(Rx) & Vinku(Tx).
Discrete power supplies are used to generate 2.8V for BT, 1.5V for the camera module, 1.3V/1.5V for Helen3 and
18V for backlight LEDs.
The device supports both 1.8V/3V SIM cards which are powered by RETU / VSIM1. RETUs VSIM2 is used to power
RS MMC 1.8V only. USB accessories which needs power from the device are powered by TAHVO / VOUT.
Because LED driver in TAHVO is not used, the external SMPS is used instead. External LED SMPS is still controlled
by TAHVO and powered by battery voltage.
System power-up
After inserting the main battery, regulators started by HW are enabled. SW checks, if there is some reason to
keep the power on. If not, the system is set to power off state by watchdog. Power up can be caused by the
following reasons:
• Power key is pressed
• Charger is connected
• RTC alarm occurs
• MBUS wake-up
After that:
• Retu activates sleep clock and VANA, VDRAM, VIO and VR1 regulators.
• Voltage appearing at Retu's RSTX pin is used for enabling Tahvo ASIC.
• Tahvo enables VCORE regulator and its internal RC-oscillator (600kHz).
• VCTCXO regulator is set ON and RF clock (main system clock) is started to produce.
• Retu will release PURX ~ 16ms after power up is enabled (the RF clock is then stable enough).
• Synchronizing clock (2.4MHz) for Tahvo is started to be produced. After PURX is released and two rising edges
of 2.4MHz synchronous clock have been detected in SMPSClk input Tahvo is starting to use that instead of
600kHz internal RC-oscillator.
• HW start-up procedure has been finalized and the system is up and running. Now it is possible for SW to
switch ON other needed regulators.
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