MAX1647 Maxim, MAX1647 Datasheet - Page 21

• Manufacturer Part Number: MAX1647
• Description: Chemistry-Independent Battery Chargers
• Manufacturer: Maxim

With SEL = AGND, R1 should be as close as possible to
0.185 / 1.023 = 181mΩ to ensure that the actual output
current matches the data value programmed with the
ChargingCurrent( ) command. With SEL = open, R1
should be as close as possible to 90mΩ. With SEL = VL,
R1 should be as close as possible to 45mΩ. Table 5 sum-
marizes how SEL affects the R1 value and the meaning of
data bits D15–D0 in the ChargingCurrent( ) command.
DA5–DA0 denote the current DAC code bits, and I4–I0
denote the IOUT linear-current source binary weighting
bits. Note that whenever any current DAC bits are set, the
linear-current source is set to full scale (31mA).
The power-on reset value for the ChargingCurrent( )
register is 0x000C. Irrespective of the SEL pin setting,
the MAX1647 powers on with I0 set to 12mA (i.e.,
DA5–DA0, I1, and I0 all equal to zero, and only I3 and
I2 set). Anytime the BATTERY_PRESENT status bit is
clear (battery removed), the ChargingCurrent( ) register
returns to its power-on reset state. This ensures that
upon insertion of a battery, the initial charging current is
12mA.
The AlarmWarning( ) command uses Write-Word protocol.
The command code for AlarmWarning( ) is 0x16; thus the
CMD7–CMD0 in Write-Word protocol should be
0b00010110. The AlarmWarning( ) command sets the
ALARM_INHIBITED status bit in the MAX1647 if D15, D14,
or D12 of the Write-Word protocol data equals 1. Table 6
summarizes the AlarmWarning( ) command’s function.
The ALARM_INHIBITED status bit remains set until
BATTERY_PRESENT = 0 (battery removed) or a
ChargerMode() command is written with the POR_RESET
bit set. As long as ALARM_INHIBITED = 1, the MAX1647
switching regulator and IOUT current source remain off.
The ChargerStatus( ) command uses Read-Word proto-
col. The command code for ChargerStatus( ) is 0x13;
thus, the CMD7–CMD0 bits in Write-Word protocol
should be 0b00010011. The ChargerStatus( ) com-
mand returns information about thermistor impedance
and the MAX1647’s internal state. The Read-Word
Table 6. Effect of the AlarmWarning( ) Command
D15 D14 D13 D12 D11
1
x
x
1
x
x
x
x
x
x
x
1
______________________________________________________________________________________
AlarmWarning( ) WRITE-WORD PROTOCOL DATA
x
x
x
D10
x
x
x
D9
x
x
x
ChargerStatus( )
AlarmWarning( )
D8
x
x
x
D7
x
x
x
D6
x
x
x
Chemistry-Independent
protocol returns D15–D0 (Figure 7). Table 7 describes
the meaning of the individual bits. The latched bits,
THERMISTOR_HOT and ALARM_INHIBITED, are
cleared whenever BATTERY_PRESENT = 0 or
ChargerMode( ) is written with POR_RESET = 1.
An interrupt is triggered (INT goes low) whenever power
is applied to DCIN, the BATTERY_PRESENT bit changes,
or the POWER_FAIL bit changes. BATTERY_PRESENT
and POWER_FAIL have interrupt masks that can be set
or cleared via the ChargerMode( ) command. INT stays
low until the interrupt is cleared. There are two methods
for clearing the interrupt: issuing a ChargerStatus( ) com-
mand, and using the Receive Byte protocol with a 0x19
Alert-Response address. The MAX1647 responds to the
Alert-Response address with the 0x89 byte.
The following pseudo-code describes an interrupt rou-
tine that is triggered by the MAX1647 INT output going
low. This interrupt routine keeps the host informed of
any changes in battery-charger status, such as DCIN
power detection, or battery removal and insertion.
DOMAX1647:
{ This is the beginning of the routine that handles
MAX1647 interrupts. }
{ Check the status of the MAX1647. }
TEMPWORD = ReadWord( SMBADDR = 0b00010011
= 0x13, COMMAND = 0x13 )
{ Check for the normal power-up case without a battery
installed. THERMISTOR_OR = 1, BATTERY_PRESENT =
0. Use 0b1011111011111111 = 0xBEFF as the mask. }
IF (TEMPWORD OR 0xBEFF) = 0xBFFF THEN GOTO
NOBATT:
{ Check to see if the battery is installed. BATTERY_
PRESENT = 1. Use 0b1011111111111111 = 0xBFFF as
the mask. }
D5
__________Applications Information
x
x
x
D4
x
x
x
Interrupts and the Alert-Response
D3
x
x
x
Battery Chargers
with Duracell Smart Batteries
D2
x
x
x
D1
x
x
x
D0
x
x
x
Using the MAX1647
Set ALARM_INHIBITED
Set ALARM_INHIBITED
Set ALARM_INHIBITED
RESULT
Address
21