MAX1660 Datasheet, PDF (11/20 Pages) Maxim Integrated Products – Digitally Controlled Fuel-Gauge Interface

Digitally Controlled
Fuel-Gauge Interface
Overcurrent Detection
The MAX1660’s precision analog interface continuously
monitors the input current to detect an overcurrent con-
dition. Figure 7 shows the functional diagram of the
overcurrent comparator section.
An overcurrent condition occurs whenever the voltage
on CS exceeds the voltage on OCI (for charging cur-
rents), or when ODI falls below ground (for discharging
currents). When an overcurrent condition occurs, the
overcurrent comparators generate an interrupt (INT
goes low) and set the OD (discharging) or OC (charg-
ing) latch, which remains set until either the configura-
tion word’s CLRINT bit is set, the MAX1660 enters soft-
shutdown mode, or the MAX1660 initiates a power-on
reset. The host defines any action taken upon receipt of
this interrupt. A logic block follows the latch, which sets
the gate-driver output’s appropriate state, as defined in
Table 4, and drives the N-channel MOSFET open-drain
gate drivers.
Although the host has complete control over the
MAX1660’s response to an overcurrent condition, take
care to ensure adequate overcurrent protection. In gen-
eral, the configuration word’s OCLO and ODLO bits
should always remain cleared. This ensures that either
the MAX1660 will be in overcurrent auto-detect mode
(the power-on-reset state), or the external FETs are
forced off (the load is disconnected). Regardless of the
OCLO and ODLO bit settings, the MAX1660 interrupts
the host (INT goes low) if the current flow exceeds the
overcurrent threshold.
When OCHI = OCLO = 1 or ODHI = ODLO = 1, the cor-
responding overcurrent comparator operates in free-
running mode, driving OCO and ODO directly. When
the current exceeds the overcurrent threshold, the
appropriate MOSFET turns off, and when the current
is below the overcurrent threshold, it turns on. Forcing
the MOSFET off prevents current from flowing, which in
turn decreases the current flow to below the over-
current threshold. A persistent overcurrent condition,
therefore, produces a pulsed output as the current flow
repeatedly crosses the overcurrent threshold. In free-
running mode, INT pulls low when the first overcurrent
condition occurs, and stays low until the interrupt is
cleared, as described in the INT Output section.
Operation in this mode requires that OCO and ODO
be buffered to ensure fast MOSFET turn-off and slow
MOSFET turn-on times. The relatively slow turn-off
response of the OCO and ODO open-drain outputs
alone is unsuitable for driving MOSFETs directly in this
mode.
a) DISCHARGING DIRECTION
ODICMP
ODSTATUS
ODO
ODI
-
+
S
OD Q
R
ODO LOGIC
b) CHARGING DIRECTION
OCI
-
CS
+
CLRINT
POWER-ON ODLO ODHI
RESET
OCICMP
OCSTATUS
OCO
S
OC Q
R
OCO LOGIC
CLRINT
POWER-ON OCLO OCHI
RESET
Figure 7. Overcurrent Comparator Section Functional Diagram
*Patent pending
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