MAX1644 Datasheet, PDF (14/32 Pages) Maxim Integrated Products – Advanced Chemistry-Independent, Level 2 Battery Charger with Input Current Limiting

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Operating Conditions
The MAX1645 changes its operation depending on the
voltages at DCIN, BATT, VDD, and THM. Several impor-
tant operating states follow:
• AC Present. When DCIN is > 7.5V, the battery is
considered to be in an AC Present state. In this con-
dition, both the LDO and REF will function properly
and battery charging is allowed. When AC is pre-
sent, the AC_PRESENT bit (bit 15) in the
ChargerStatus() register is set to “1.”
• Power Fail. When DCIN is < BATT + 0.3V, the
MAX1645 is in the Power Fail state, since the charger
doesn’t have enough input voltage to charge the bat-
tery. In Power Fail, the PDS input PMOS switch is
turned off and the POWER_FAIL bit (bit 13) in the
ChargerStatus() register is set to “1.”
• Battery Present. When THM is < 91% of VDD, the
battery is considered to be present. The MAX1645
uses the THM pin to detect when a battery is con-
nected to the charger. When the battery is present,
the BATTERY_PRESENT bit (bit 14) in the
ChargerStatus() register is set to “1” and charging
can proceed. When the battery is not present, all of
the MAX1645 registers are reset. With no battery pre-
sent, the charger will still try to regulate the BATT pin
voltage at 18.432V with 128mA of current compliance.
• Battery Undervoltage. When BATT < 2.5V, the bat-
tery is in an undervoltage state. This causes the
charger to reduce its current compliance to 128mA.
The content of the ChargingCurrent() register is unaf-
fected and, when the BATT voltage exceeds 2.7V,
normal charging resumes. ChargingVoltage() is unaf-
fected and can be set as low as 1.024V.
• VDD Undervoltage. When VDD < 2.5V, the VDD sup-
ply is in an undervoltage state, and the SMBus inter-
face will not respond to commands. Coming out of
the undervoltage condition, MAX1645 will be in its
Power-On Reset state. No charging will occur when
VDD is under voltage.
SMBus Interface
The MAX1645 receives control inputs from the SMBus
interface. The serial interface complies with the SMBus
specification (refer to the System Management Bus
Specification from Intel Corporation). Charger function-
ality complies with the Intel/Duracell Smart Charger
Specification for a Level 2 charger.
The MAX1645 uses the SMBus Read-Word and Write-
Word protocols to communicate with the battery being
charged, as well as with any host system that monitors
the battery-to-charger communications as a Level 2
SMBus charger. The MAX1645 is an SMBus slave
device and does not initiate communication on the bus.
It receives commands and responds to queries for sta-
tus information. Figure 3 shows examples of the SMBus
Write-Word and Read-Word protocols, and Figures 4
and 5 show the SMBus serial-interface timing.
Each communication with the MAX1645 begins with the
MASTER issuing a START condition that is defined as a
falling edge on SDA with SCL high and ends with a
STOP condition defined as a rising edge on SDA with
SCL high. Between the START and STOP conditions,
the device address, the command byte, and the data
bytes are sent. The MAX1645 device address is 0x12
and supports the charger commands as described in
Tables 1–6.
Battery Charger Commands
ChargerSpecInfo()
The ChargerSpecInfo() command uses the Read-Word
protocol (Figure 3b). The command code for
ChargerSpecInfo() is 0x11 (0b00010001). Table 1 lists
the functions of the data bits (D0–D15). Bit 0 refers to
the D0 bit in the Read-Word protocol. The MAX1645 is
version 1.0; therefore, the ChargerSpecInfo() command
returns 0x01.
ChargerMode()
The ChargerMode() command uses the Write-Word
protocol (Figure 3a). The command code for
ChargerMode() is 0x12 (0b00010010). Table 2 lists the
functions of the data bits (D0–D15). Bit 0 refers to the
D0 bit in the Write-Word protocol.
To charge a battery that has a thermistor impedance in
the HOT range (i.e., THERMISTOR_HOT = 1 and THER-
MISTOR_UR = 0), the host must use the Charger
Mode() command to clear HOT_STOP after the battery
is inserted. The HOT_STOP bit returns to its default
power-up condition (“1”) whenever the battery is
removed.
ChargerStatus()
The ChargerStatus() command uses the Read-Word
protocol (Figure 3b). The command code for Charger
Status() is 0x13 (0b00010011). Table 3 describes the
functions of the data bits (D0–D15). Bit 0 refers to the
D0 bit in the Read-Word protocol.
The ChargerStatus() command returns information
about thermistor impedance and the MAX1645’s inter-
nal state. The latched bits, THERMISTOR_HOT and
ALARM_INHIBITED, are cleared whenever BATTERY_
PRESENT = 0 or ChargerMode() is written with
POR_RESET = 1. The ALARM_INHIBITED status bit can
also be cleared by writing a new charging current OR
charging voltage.
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