LTC4000_15 Datasheet, PDF (8/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging and Power Management

LTC4000
Pin Functions (QFN/SSOP)
VM (Pin 1/Pin 25): Voltage Monitor Input. High impedance
input to an accurate comparator with a 1.193V threshold
(typical). This pin controls the state of the RST output
pin. Connect a resistor divider (R_VM1, R_VM2) between the
monitored voltage and GND, with the center tap point con-
nected to this pin. The falling threshold of the monitored
voltage is calculated as follows:
V_{VM _ RST}
=
R_VM1 + R_VM2
R_VM2
• 1.193V
where R_VM2 is the bottom resistor between the VM pin
and GND. Tie to the BIAS pin if voltage monitoring func-
tion is not used.
RST (Pin 2/Pin 26): High Voltage Open Drain Reset Output.
When the voltage at the VM pin is below 1.193V, this status
pin is pulled low. When driven low, this pin can disable
a DC/DC converter when connected to the converter’s
enable pin. This pin can also drive an LED to provide a
visual status indicator of a monitored voltage. Short this
pin to GND when not used.
IIMON (Pin 3/Pin 27): Input Current Monitor. The voltage
on this pin is 20 times (typical) the sense voltage (V_IN,CLN)
across the input current sense resistor(R_IS), therefore
providing a voltage proportional to the input current.
Connect an appropriate capacitor to this pin to obtain a
voltage representation of the time-average input current.
Short this pin to GND to disable input current limit feature.
IL (Pin 4/Pin 28): Input Current Limit Programming. Con-
nect the input current programming resistor (R_IL) to this
pin. This pin sources 50µA of current. The regulation loop
compares the voltage on this pin with the input current
monitor voltage (V_IIMON), and drives the ITH pin accord-
ingly to ensure that the programmed input current limit is
not exceeded. The input current limit is determined using
the following formula:
I_ILIM
=
2.5µA
•



R_IL
R_IS



where R_IS is the sense resistor connected to the IN and
the CLN pins. Leave the pin open for the maximum input
current limit of 50mV/R_IS.
ENC (Pin 5/Pin 1): Enable Charging Pin. High impedance
digital input pin. Pull this pin above 1.5V to enable charg-
ing and below 0.5V to disable charging. Leaving this pin
open causes the internal 2µA pull-up current to pull the
pin to 2.5V (typical).
IBMON (Pin 6/Pin 2): Battery Charge Current Monitor. The
voltage on this pin is 20 times (typical) the sense voltage
(V_CSP,CSN) across the battery current sense resistor (R_CS),
therefore providing a voltage proportional to the battery
charge current. Connect an appropriate capacitor to this
pin to obtain a voltage representation of the time-average
battery charge current. Short this pin to GND to disable
charge current limit feature.
CX (Pin 7/Pin 3): Charge Current Termination Pro-
gramming. Connect the charge current termination pro-
gramming resistor (R_CX) to this pin. This pin is a high
impedance input to a comparator and sources 5μA of
current. When the voltage on this pin is greater than the
charge current monitor voltage (V_IBMON), the CHRG pin
turns high impedance indicating that the CX threshold is
reached. When this occurs, the charge current is imme-
diately terminated if the TMR pin is shorted to the BIAS
pin, otherwise charging continues until the charge termi-
nation timer expires. The charge current termination value
is determined using the following formula:
( ) _{IC/X =}
0.25µA • R_CX
R_CS
− 0.5mV
Where R_CS is the sense resistor connected to the CSP
and the CSN pins. Note that if R_CX = R_CL ≤ 19.1kΩ, where
R_CL is the charge current programming resistor, then the
charge current termination value is one tenth the full charge
current, more familiarly known as C/10. Short this pin to
GND to disable CX termination.
CL (Pin 8/Pin 4): Charge Current Limit Programming. Con-
nect the charge current programming resistor (R_CL) to this
pin. This pin sources 50µA of current. The regulation loop
compares the voltage on this pin with the charge current
monitor voltage (V_IBMON), and drives the ITH pin accord-
ingly to ensure that the programmed charge current limit
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