LTC4000 Datasheet, PDF (10/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging and Power Management

LTC4000
Pin Functions (QFN/SSOP)
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 immedi-
ate valid voltage level at the output when the LTC4000 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 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).
OFB (Pin 21/Pin 17): Output Feedback Voltage Pin. This
pin is a high impedance input pin used to sense the output
voltage level. In regulation, the output voltage loop sets the
voltage on this feedback pin to 1.193V. Connect this pin
to the center node of a resistor divider between the CSP
pin and the FBG pin to set the output voltage when battery
charging is terminated and all the output load current is
provided from the input. The output voltage can then be
obtained as follows:
V_OUT
=
R_OFB2 + R_OFB1
R_OFB2
•
1.193V
When charging a heavily discharged battery (such that V_OFB
< V_{OUT(INST_ON)}), the battery PowerPath PMOS connected
to BGATE is regulated to set the voltage on this feedback
pin to 0.974V (approximately 86% of the battery float
voltage). The instant-on output voltage is then as follows:
V_{OUT(INST _ ON)}
=
R_OFB2 + R_OFB1
R_OFB2
•
0.974V
IGATE (Pin 22/Pin 18): Input PMOS Gate Drive Output. The
IGATE pin drives the external PMOS to behave as an ideal
diode from the IID pin (anode) to the CSP pin (cathode).
IID (Pin 23/Pin 19): Input Ideal Diode Anode. This pin is
the anode of the input ideal diode driver (the cathode is
the CSP pin).
ITH (Pin 24/Pin 20): High Impedance Control Voltage Pin.
When any of the regulation loops (input current, charge
current, battery float voltage or the output voltage) indicate
that its limit is reached, the ITH pin will sink current (up to
1mA) to regulate that particular loop at the limit. In many
applications, this ITH pin is connected to the control/com-
pensation node of a DC/DC converter. Without any external
pull-up, the operating voltage range on this pin is GND to
2.5V. With an external pull-up, the voltage on this pin can
be pulled up to 6V. Note that the impedance connected to
this pin affects the overall loop gain. For details, refer to
the Applications Information section.
4000f
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