LTC2938/LTC2939
7
293839ff
PIN FUNCTIONS
V
PG
: Threshold Select Input. Connect to an external 1%
resistive divider between V
REF
and GND to select one of
sixteen combinations of voltage thresholds (see Table 1).
Do not add capacitance to the V
PG
input.
V
REF
: Buffered Reference Voltage Output. A 1.210V nomi-
nal reference used for the mode selection voltage (V
PG
)
and for the offset of negative adjustable applications. The
buffered reference can source and sink up to 1mA. The
reference can drive a bypass capacitor of up to 1000pF
without oscillation.
WDI: Watchdog Input: A three-state input that controls
the operation of the watchdog timer. Leaving the WDI pin
unconnected disables the watchdog timer while tying it
low or high enables it. While RST is high, a transition
between low and high logic levels (rising or falling edge)
within the watchdog timeout period is required to inhibit
WDO from pulling low and a watchdog initiated reset. A
capacitor attached to CWT sets the watchdog timeout
period. A transition between the low and high logic levels
on the WDI input clears the voltage on the CWT capacitor,
preventing WDO from going low. Once WDO is latched
low, WDI must transition between low and high logic levels
to clear WDO Transitions between open and logic low or
logic high do not clear WDO.
WDO: Watchdog Output. Logic output with weak 6μA pull-
up to V2. May be pulled greater than V2 using external
pull-up. For V2 confi gured to monitor 2.5V or below,
connect an external pull-up resistor to the interface logic
supply to ensure that the output high voltage is above the
V
IH
of the external circuit. The watchdog timer is enabled
when RST is high. The watchdog output pulls low if the
watchdog timer expires and the output remains low
until set high by the next WDI transition or anytime an
undervoltage condition occurs. A watchdog failure also
triggers a reset event. Leave open if unused.
Exposed Pad (DE12 package only): The Exposed Pad may
be left open or connected to device ground.
will vary depending on parasitic capacitance on the pin.
Tie CWT to GND to disable the watchdog function.
GND: Device Ground.
NC: No Internal Connection.
RST: Reset Output. Logic output with weak 6μA pull-up
to V2. Pulls low when any voltage input is below the reset
threshold and held low for the confi gured reset delay time
after all voltage inputs are above threshold. When the
watchdog timer is enabled but not serviced prior to the
confi gured watchdog timeout period, RST pulls low for
one reset delay time. May be pulled to greater than V2
using an external pull-up. For V2 confi gured to monitor
2.5V or below, connect an external pull-up resistor to
the interface logic supply to ensure that the output high
voltage is above the V
IH
of the external circuit. Leave
open if unused.
V1: Voltage Input 1. Select from 5V or 3.3V. See the Ap-
plications Information section for details. The greater of
V1 or V2 is also V
CC
for the device. Bypass this input to
ground with a 0.1μF (or greater) capacitor.
V2: Voltage Input 2. Select from 3.3V, 2.5V, 1.8V, 1.5V or
1.2V. See the Applications Information section for details.
The greater of V1, V2 is also V
CC
for the device. Bypass
this input to ground with a 0.1μF (or greater) capacitor.
All status outputs are weakly pulled up to V2.
V3: Voltage Input 3. Select from 2.5V, 1.8V, 1.5V, 1.2V or
ADJ. See the Applications Information section for details.
Tie to V1 if unused.
V4: Voltage Input 4. Select from 1.8V, 1.5V, 1.2V, ADJ or
–ADJ. See the Applications Information section for details.
Tie to V1 if unused and confi gured for positive voltage.
V5: Adjustable Voltage Input 5 for LTC2939. High imped-
ance comparator input with 0.5V typical threshold. Tie to
V1 if unused.
V6: Adjustable Voltage Input 6 for LTC2939. High imped-
ance comparator input with 0.5V typical threshold. Tie to
V1 if unused.
