The DC/DC converter is the only unit which draws current from the 2 cell NiMH battery pack. The battery voltage, Vb, is up converted through the DC/DC converter to an output voltage level, Vdc_out, which is dependent on the phone state (operating mode) and in call mode depending upon which band and on what power level the phone is transmitting at.
The DC/DC converter feeds power directly to four parts of the system: the CCONT, the power amplifier, the UI (buzzer, Vibra, display- and keyboard- lights) and for a separate regulator in the RF. The Baseband contains components that control power distribution to the whole phone, except for the PA control in RF.
The battery consists of two NiMH cells and a polyswitch, all assembled into the battery pack. An external charger can be used for recharging the battery and supplying power to the phone. The charger can be either a two wire type of charger, or a 3-wire charger, so called performance charger.
The power management circuit PSCC provides protection against over voltages, charger failures and pirate chargers etc. that would otherwise cause damage to the phone.
Ctrl i m m
Figure 10. Baseband power Distribution
The DC/DC-converter principal implementation in NSE-8/9 is shown Figure 11. V105 is the switcher ic, TEA1210 which contains the control logic together with the switching transistors.
R102, R105 and R112 forms the main voltage divider for the feedback voltage to the FB pin. The switcher will adjust the output voltage in order to achieve 1.24V at the FB pin. The two transistors V108a & b forms together with R113 and R114 a simple 2 bit DAC, which depending upon the control signals Vcon_1 (LSB) and Vcon_2 (MSB) from the MAD2PR1, changes the voltage divider. V105 responds by changing Vdc_out in order to keep the voltage on the FB pin constant.
The voltage control has been implemented to reduce Baseband loss in idle mode and PA loss at low Tx power levels while achieving better conversion efficiency due to lower conversion ratio. Additionally at high power levels it is necessary to increase the output voltage to accommodate the PA current consumption which exceeds the current capability of the converter IC.
The main portion of the power for the PAs during Tx burst are supplied by the output capacitors, C109 - C113, the switcher current being limited to 1.6 A in burst, and 1.0 A in between bursts. The capacitors are recharged in between the Tx bursts, with less current to obtain a better converter efficiency. The output voltage is selected as low as possible, but still sufficiently high, in order to prevent Vdc_out from dropping below the CCONT regulation level of 3.1V, due to the current drawn during Tx burst.
LX Vout RLimH
ILimSel. U/D GND FR
MAD2PR1 LOW BATT
C109 470u .C110 470u
C111 112 C113
MAD2PR1 VCON 2
Figure 11. DC/DC Converter
The 5 x 470uF output capacitors has been chosen to have low ESR to achieve a compromise between output ripple, drop during Tx burst, conversion ratio and efficiency.
The TXP from MAD2PR1 selects between two current limits, determined by R108 and R109. TXP is active during the TX burst thus commanding a higher current through the converter without saturating the coil L102. In between the Tx bursts, when in call, the switcher current is lowered for efficiency reasons, but still insuring full re-charge of the output capacitors at the succeeding Tx burst.
The switching frequency is app. 600 KHz and in order to avoid emission in neighboring channels, due to the PA being supplied from Vdc_out a ferrite bead, L103 is inserted to attenuate the switching frequency.
The schottky diode, V101 is only conducting during the small time when power FET conduction inside V105 is shifted.
The resistors R131 and R132 forms together with the transistor V109a and R134 a circuit which will shut down the switcher when the battery voltage reaches 1.4V in order not to drain the battery below a limit of insufficient current capability. Additionally this circuit generates via V109b an interrupt to the MAD2PR1 SIMCardDetX, when the battery is removed, in order to insure the proper shutdown sequence of the SIM card.
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