LTC4261 datasheet(8/34 Pages) AD

8 / 34 page

LTC2945

Rev. C

For more information www.analog.com

PIN FUNCTIONS

INTVCC (Pin 1/Pin 2): Internal Low Voltage Supply Input/

Output. This pin is used to power internal circuitry. It can

be configured as a direct input for a low voltage supply, as

linear regulator from higher voltage supply connected to

VDD, or as a shunt regulator. Connect this pin directly to a

2.7V to 5.9V supply if available. When INTVCC is powered

from an external supply, short the VDD pin to INTVCC. If

VDD is connected to a 4V to 80V supply, INTVCC becomes

the 5V output of an internal series regulator that can sup-

ply up to 10mA to external circuitry. For even higher sup-

ply voltages or if a floating topology is desired, INTVCC can

be used as a 6.3V shunt regulator. Connect the supply to

INTVCC through a shunt resistor that limits the current to

less than 35mA. An undervoltage lockout circuit disables

the ADC when the voltage at this pin drops below 2.5V.

Connect a bypass capacitor between 0.1µF and 1µF from

this pin to ground.

ADR1, ADR0 (Pins 2, 3/Pins 3, 4): I2C Device Address

Inputs. Connecting these pins to INTVCC, GND or leaving

the pins open configures one of nine possible addresses.

See Table 1 in Applications Information section for details.

ADIN (Pin 4/Pin 5): ADC Input. The onboard ADC mea-

sures voltages between 0V and 2.048V. Tie to ground

if unused.

GND (Pin 5/Pin 6): Device Ground.

SCL (Pin 6/Pin 7): I2C Bus Clock Input. Data at the SDAI

pin is shifted in or out on rising edges of SCL. This pin

is driven by an open-collector output from a master con-

troller. An external pull-up resistor or current source is

required and can be placed between SCL and VDD or

INTVCC. The voltage at SCL is internally clamped to 6.4V

(5.9V minimum)

SDAI (Pin 7/Pin 8): I2C Bus Data Input. Used for shifting

in address, command or data bits. This pin is driven by an

open-collector output from a master controller. An exter-

nal pull-up resistor or current source is required and can

be placed between SDAI and VDD or INTVCC. The voltage

at SDAI is internally clamped to 6.4V (5.9V minimum)

SDAO (Pin 8/Pin 9): I2C Bus Data Output. Open-drain

output used for sending data back to the master controller

or acknowledging a write operation. An external pull-up

resistor or current source is required.

SDAO (Pin 8/Pin 9, LTC2945-1 Only): Inverted I2C Bus

Data Output. Open-drain output used for sending data

back to the master controller or acknowledging a write

operation. Data is inverted for convenience of opto-iso-

lation. An external pull-up resistor or current source is

required.

ALERT (Pin 9/Pin 10): Fault Alert Output. Open drain logic

output that is pulled to ground after an ADC conversion

resulted in a fault to alert the host controller. A fault alert is

enabled by setting the corresponding bit in the ALERT reg-

ister as shown in Table 4. This device is compatible with

the SMBus alert protocol. See Applications Information.

Tie to ground if unused.

SENSE– (Pin 10/Pin 11): Current Sense Input. Connect

an external sense resistor between SENSE+ and SENSE–.

The differential voltage between SENSE+ and SENSE– is

monitored by the onboard ADC with a full-scale sense

voltage of 102.4mV.

SENSE+ (Pin 11/Pin 12): Supply Voltage and Current

Sense Input. Used as a supply and current sense input

for the internal current sense amplifier. The voltage at this

pin is monitored by the onboard ADC with a full-scale

input range of 102.4V. See Figure 17 for recommended

Kelvin connection.

VDD (Pin 12/Pin 1): High Voltage Supply Input. This pin

powers an internal series regulator with input voltages

ranging from 4V to 80V and produces 5V at INTVCC when

the input voltage is above 7V. Connect a bypass capacitor

between 0.1µF and 1µF from this pin to ground if external

load is present on the INTVCC pin. The onboard 12-bit ADC

can be configured to monitor the voltage at VDD with a

full-scale input range of 102.4V.

EXPOSED PAD (Pin 13, UD Package Only): Exposed pad

may be left open or connected to device ground. For best

thermal performance, connect to a large PCB area.

(QFN/MSOP)

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