LTC3576 Datasheet, PDF (13/48 Pages) Linear Technology – Switching Power Manager with USB On-the-Go + Triple Step-Down DC/DCs

LTC3576/LTC3576-1
PIN FUNCTIONS
CLPROG (Pin 1): USB Current Limit Program and Monitor
Pin. A 1% resistor from CLPROG to ground determines
the upper limit of the current drawn or sourced from the
V_BUS pins. A precise fraction, h_CLPROG, of the V_BUS cur-
rent is sent to the CLPROG pin when the PMOS switch of
the PowerPath switching regulator is on. The switching
regulator delivers power until the CLPROG pin reaches
1.18V in step-down mode and 1.15V in step-up mode.
When the switching regulator is in step-down mode,
CLPROG is used to regulate the average input current.
Several V_BUS current limit settings are available via user
input which will typically correspond to the 500mA and
100mA USB specifications. When the switching regulator
is in step-up mode (USB on-the-go), CLPROG is used to
limit the average output current to 680mA. A multilayer
ceramic averaging capacitor or R-C network is required
at CLPROG for filtering.
LDO3V3 (Pin 2): 3.3V LDO Output Pin. This pin provides
a regulated always-on 3.3V supply voltage. LDO3V3
gets its power from V_OUT. It may be used for light loads
such as a watchdog microprocessor or real time clock.
A 1μF capacitor is required from LDO3V3 to ground. If
the LDO3V3 output is not used it should be disabled by
connecting it to V_OUT.
NTCBIAS (Pin 3): NTC Thermistor Bias Output. If NTC
operation is desired, connect a bias resistor between
NTCBIAS and NTC, and an NTC thermistor between NTC
and GND. To disable NTC operation, connect NTC to GND
and leave NTCBIAS open.
NTC (Pin 4): Input to the Thermistor Monitoring Circuits.
The NTC pin connects to a negative temperature coefficient
thermistor, which is typically co-packaged with the battery,
to determine if the battery is too hot or too cold to charge.
If the battery’s temperature is out of range, charging is
paused until it re-enters the valid range. A low drift bias
resistor is required from NTCBIAS to NTC and a thermistor
is required from NTC to ground. To disable NTC operation,
connect NTC to GND and leave NTCBIAS open.
OVGATE (Pin 5): Overvoltage Protection Gate Output.
Connect OVGATE to the gate pin of an external N-channel
MOS pass transistor. The source of the transistor should
be connected to V_BUS and the drain should be connected
to the product’s DC input connector. In the absence of an
overvoltage condition, this pin is connected to an internal
charge pump capable of creating sufficient overdrive to fully
enhance the pass transistor. If an overvoltage condition is
detected, OVGATE is brought rapidly to GND to prevent
damage to the LTC3576/LTC3576-1. OVGATE works in
conjunction with OVSENS to provide this protection.
OVSENS (Pin 6): Overvoltage Protection Sense Input.
OVSENS should be connected through a 6.2k resistor to
the input power connector and the drain of an external
N-channel MOS pass transistor. When the voltage on this
pin exceeds V_OVCUTOFF, the OVGATE pin will be pulled
to GND to disable the pass transistor and protect the
LTC3576/LTC3576-1. The OVSENS pin shunts current
during an overvoltage transient in order to keep the pin
voltage at 6V.
FB1 (Pin 7): Feedback Input for Switching Regulator 1.
When regulator 1’s control loop is complete, this pin servos
to 1 of 16 possible set points based on the commanded
value from the I²C serial port. See Table 4.
V_IN1 (Pin 8): Power Input for Switching Regulator 1.
This pin will generally be connected to V_OUT. A 1μF MLCC
capacitor is recommended on this pin.
SW1 (Pin 9): Power Transmission Pin for Switching
Regulator 1.
EN1 (Pin 10): Logic Input. This logic input pin indepen-
dently enables switching regulator 1. Active high. This
pin is logically ORed with its corresponding bit in the
I²C serial port. See Table 3. Has a 2μA internal pull-down
current source.
ENOTG (Pin 11): Logic Input. This logic input pin inde-
pendently enables the bidirectional switching regulator to
step up the voltage on V_OUT and provide a 5V output on
V_BUS for USB on-the-go applications. Active high. This
pin is logically ORed with its corresponding bit in the
I²C serial port. See Table 3. Has a 2μA internal pull-down
current source.
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