LTC4000-1 Datasheet, PDF (10/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

LTC4000-1
Pin Functions (QFN/SSOP)
NTC (Pin 14/Pin 10): Thermistor Input. Connect a ther-
mistor from NTC to GND, and a corresponding resistor
from BIAS to NTC. The voltage level on this pin determines
if the battery temperature is safe for charging. The charge
current and charge timer are suspended if the thermistor
indicates a temperature that is unsafe for charging. Once the
temperature returns to the safe region, charging resumes.
Leave the pin open or connected to a capacitor to disable
the temperature qualified charging function.
FBG (Pin 15/Pin 11): Feedback Ground Pin. This is the
ground return pin for the resistor dividers connected to
the BFB and OFB pins. As soon as the voltage at IN is valid
(>3V typical), this pin has a 100Ω resistance to GND. When
the voltage at IN is not valid, this pin is disconnected from
GND to ensure that the resistor dividers connected to the
BFB and OFB pins do not continue to drain the battery
when the battery is the only available power source.
BFB (Pin 16/Pin 12): Battery Feedback Voltage Pin. This
pin is a high impedance input pin used to sense the battery
voltage level. In regulation, the battery float voltage loop
sets the voltage on this pin to 1.136V (typical). Connect
this pin to the center node of a resistor divider between
the BAT pin and the FBG pin to set the battery float voltage.
The battery float voltage can then be obtained as follows:
V_FLOAT
=
R_BFB2 + R_BFB1
R_BFB2
•
1.136V
BAT (Pin 17/Pin 13): Battery Pack Connection. Connect
the battery to this pin. This pin is the anode of the battery
ideal diode driver (the cathode is the CSN pin).
BGATE (Pin 18/Pin 14): External Battery PMOS Gate Drive
Output. When not charging, the BGATE pin drives the
external PMOS to behave as an ideal diode from the BAT
pin (anode) to the CSN pin (cathode). This allows efficient
delivery of any required additional power from the battery
to the downstream system connected to the CSN pin.
When charging a heavily discharged battery, the BGATE
pin is regulated to set the output feedback voltage (OFB
pin) to 86% of the battery float voltage (0.974V typical).
This allows the instant-on feature, providing an immediate
valid voltage level at the output when the LTC4000-1 is
charging a heavily discharged battery. Once the voltage
on the OFB pin is above the 0.974V typical value, then the
BGATE pin is driven low to ensure an efficient charging
path from the CSN pin to the BAT pin.
CSN (Pin 19/Pin 15): Charge Current Sense Negative Input
and Battery Ideal Diode Cathode. Connect a sense resistor
between this pin and the CSP pin. The LTC4000-1 senses
the voltage across this sense resistor and regulates it to a
voltage equal to 1/20th (typical) of the voltage set at the
CL pin. The maximum regulated sense voltage is 50mV.
The CSN pin is also the cathode input of the battery ideal
diode driver (the anode input is the BAT pin). Tie this pin
to the CSP pin if no charge current limit is desired. Refer to
the Applications Information section for complete details.
CSP (Pin 20/Pin 16): Charge Current Sense Positive Input
and Input Ideal Diode Cathode. Connect a sense resis-
tor between this pin and the CSN pin for charge current
sensing and regulation. This input should be tied to CSN
to disable the charge current regulation function. This
pin is also the cathode of the input ideal diode driver (the
anode is the IID pin).
40001f
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