LTC4040_15 Datasheet, PDF (17/26 Pages) Linear Technology – 2.5A Battery Backup Power Manager

LTC4040
Operation
OPTIONAL INPUT OVERVOLTAGE PROTECTION (OVP)
The LTC4040 can protect itself from the inadvertent
application of excessive voltage with just two external
components: an N-channel FET (MN1) and a 6.2k resis-
tor as shown in the Block Diagram. The maximum safe
overvoltage magnitude will be determined by the choice of
external NMOS and its associated drain breakdown voltage.
The optional overvoltage protection (OVP) module consists
of two pins. The first, OVSNS, is used to measure the applied
voltage through an external resistor. The second, IGATE,
is an output used to drive the gate pins of two external N-
channel FETs, MN1 and MN2 (Block Diagram). The voltage
at the OVSNS pin will be lower than the OVP input voltage
by about 250mV due to the OVP circuit’s quiescent cur-
rent flowing through the OVSNS resistor. When OVSNS is
below 6V, an internal charge pump will drive IGATE to ap-
proximately 1.88 • V_OVSNS. This will enhance the N‑channel
FETs and provide a low impedance connection to V_SYS and
power the chip. If OVSNS should rise above 6V due to a
fault, IGATE will be pulled down to ground, disabling the
external FETs to protect downstream circuitry. At the same
time, the backup boost converter will be activated to supply
the system load from the battery. When the voltage drops
below 6V again, the external FETs will be re-enabled. If the
OVP feature is not desired, remove MN1, short OVSNS to
V_IN and apply external power directly to V_IN.
SHUTDOWN MODE OPERATION
The LTC4040 can be shutdown almost entirely by pulling
both CHGOFF and BSTOFF pin above 1.2V. In this mode,
the internal charge pump is shutdown and IGATE is pulled
to ground disconnecting the forward path from input to
output via the external FETs. Only the internal OVP shunt
regulator remains active to monitor the input supply for
any possible overvoltage condition and consumes about
25µA via the OVSNS pin. Total current draw from the BAT
pin drops to below 3µA during shutdown.
For more information www.linear.com/LTC4040
4040fa
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