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Datasheet MAX1647 - Chemistry-Independent Battery Chargers - Maxim Integrated Products

Chemistry-Independent Battery ChargersMAX1647/MAX1648

Table 4. Relationship Between Current DAC Code and the ChargingCurrent( ) Value

Note 1:Logical AND of THERMISTOR_HOT, HOT_STOP, NOT(THERMISTOR_UR).Note 2:Value of CURRENT_OR bit in the ChargerStatus( ) register.N/C = No change

Table 5. Effect of SEL Pin-Strapping on the ChargingCurrent( ) Data Bits

*When SEL = VL, D5 = 1 forces DA0 to be 1 regardless of the D6 bit value.

With the switching regulator on, the current through R1(Figure 3) is regulated by sensing the average voltagebetween CS and BATT. A 6-bit current DAC controlsthe current-limit set point. DA5–DA0 denote the bits inthe current DAC code. Figure 9 shows the relationshipbetween the current DAC code and the average volt-age between CS and BATT.

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When the switching regulator is off, DHI is forced to LX and DLO is forced to ground. This prevents currentfrom flowing through inductor L1. Table 4 shows therelationship between the ChargingCurrent( ) registervalue and the switching regulator current DAC code.

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Datasheet MAX1647 - Chemistry-Independent Battery Chargers - Maxim Integrated Products

Chemistry-Independent

Battery Chargers

With SEL = AGND, R1 should be as close as possible to0.185 / 1.023 = 181m to ensure that the actual outputcurrent matches the data value programmed with theChargingCurrent( ) command. With SEL = open, R1should be as close as possible to 90m . With SEL = VL,R1 should be as close as possible to 45m . Table 5 sum-marizes how SEL affects the R1 value and the meaning ofprotocol returns D15–D0 (Figure 7). Table 7 describesthe meaning of the individual bits. The latched bits,THERMISTOR_HOT and ALARM_INHIBITED, arecleared whenever BATTERY_PRESENT = 0 orChargerMode( ) is written with POR_RESET = 1.

Interrupts and the Alert-Response

data bits D15–D0 in the ChargingCurrent( ) command.Address

DA5–DA0 denote the current DAC code bits, and I4–I0An interrupt is triggered (INTgoes low) whenever powerdenote the IOUT linear-current source binary weightingis applied to DCIN, the BATTERY_PRESENT bit changes,bits. Note that whenever any current DAC bits are set, theor the POWER_FAIL bit changes. BATTERY_PRESENTlinear-current source is set to full scale (31mA).

and POWER_FAIL have interrupt masks that can be setThe power-on reset value for the ChargingCurrent( )or cleared via the ChargerMode( ) command. INTstaysregister is 0x000C. Irrespective of the SEL pin setting,low until the interrupt is cleared. There are two methodsthe MAX1647 powers on with I0 set to 12mA (i.e.,for clearing the interrupt: issuing a ChargerStatus( ) com-DA5–DA0, I1, and I0 all equal to zero, and only I3 andmand, and using the Receive Byte protocol with a 0x19I2 set). Anytime the BATTERY_PRESENT status bit isAlert-Response address. The MAX1647 responds to theclear (battery removed), the ChargingCurrent( ) registerAlert-Response address with the 0x89 byte.

returns to its power-on reset state. This ensures thatupon insertion of a battery, the initial charging current is__________Applications Information

12mA.

Using the MAX1647

AlarmWarning( )

with Duracell Smart Batteries

The AlarmWarning( ) command uses Write-Word protocol.The following pseudo-code describes an interrupt rou-The command code for AlarmWarning( ) is 0x16; thus thetine that is triggered by the MAX1647 INToutput goingCMD7–CMD0 in Write-Word protocol should below. This interrupt routine keeps the host informed of0b00010110. The AlarmWarning( ) command sets theany changes in battery-charger status, such as DCINALARM_INHIBITED status bit in the MAX1647 if D15, D14,power detection, or battery removal and insertion.or D12 of the Write-Word protocol data equals 1. Table 6DOMAX1647:

summarizes the AlarmWarning( ) command’s function. { This is the beginning of the routine that handlesThe ALARM_INHIBITED status bit remains set until MAX1647 interrupts. }

BATTERY_PRESENT = 0 (battery removed) or a{ Check the status of the MAX1647. }

ChargerMode() command is written with the POR_RESETTEMPWORD = ReadWord( SMBADDR = 0b00010011bit set. As long as ALARM_INHIBITED = 1, the MAX1647= 0x13, COMMAND = 0x13 )

switching regulator and IOUT current source remain off.{ Check for the normal power-up case without a batteryinstalled. THERMISTOR_OR = 1, BATTERY_PRESENT =ChargerStatus( )

0. Use 0b1011111011111111 = 0xBEFF as the mask. }The ChargerStatus( ) command uses Read-Word proto-IF (TEMPWORD OR 0xBEFF) = 0xBFFF THEN GOTOcol. The command code for ChargerStatus( ) is 0x13;NOBATT:

thus, the CMD7–CMD0 bits in Write-Word protocol{ Check to see if the battery is installed. BATTERY_should be 0b00010011. The ChargerStatus( ) com-PRESENT = 1. Use 0b1011111111111111 = 0xBFFF asmand returns information about thermistor impedancethe mask. }

and the MAX1647’s internal state. The Read-Word

Table 6. Effect of the AlarmWarning( ) Command

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MAX1647/MAX1648