Datasheet LTM8028 (Analog Devices) - 7

LTM8028
pin FuncTions VOUT (Bank 1):
Power Output Pins. Apply the output filter error at the point of load. Connecting the SENSEP pin at capacitor and the output load between these and the GND the load instead of directly to VOUT eliminates this voltage pins. error. The SENSEP pin input bias current depends on the
BKV (Bank 2):
Buck Regulator Output. Apply the step-down selected output voltage. SENSEP pin input current varies regulator’s bulk capacitance here (refer to Table 1). Do not from 50μA typically at VOUT = 0.8V to 300μA typically at connect this to the load. Do not drive a voltage into BKV. VOUT = 1.8V. SENSEP must be connected to VOUT, either locally or remotely.
GND (Bank 3):
Tie these GND pins to a local ground plane below the LTM8028 and the circuit components. In most
VOB (Pin B5):
Bias for VO0, VO1, VO2. This is a 3.3V source applications, the bulk of the heat flow out of the LTM8028 to conveniently pull up the VO0, VO1, VO2 pins, if desired. is through these pads, so the printed circuit design has a If not used, leave this pin floating. large impact on the thermal performance of the part. See
PGOOD (Pin B7):
Power Good. Open drain signal that will the PCB Layout and Thermal Considerations sections for be high impedance if: more details. • The output rises above 90% of the target voltage
VIN (Bank 4):
The VIN pin supplies current to the LTM8028’s • The output stays above 85% of target voltage internal regulator and to the internal power switch. This pin must be locally bypassed with an external, low ESR • The output linear regulator does not overheat capacitor; see Table 1 for recommended values. Please see the Application Information section for more
VO0, VO1, VO2 (Pin A6, Pin B6, Pin A5):
Output Voltage details. If not used, tie PGOOD to GND. Select. These three-state pins combine to select a nominal
I
output voltage from 0.8V to 1.8V in increments of 50mV. See
MAX (Pin D1):
Sets the Maximum Output Current. Con- nect a resistor/ NTC thermistor network to the I Table 2 in the Applications Information section that defines MAX pin to reduce the maximum regulated output current of the the VO2, VO1 and VO0 settings versus VOUT. LTM8028 in response to temperature. This pin is internally
MARGA (Pin A7):
Analog Margining: This pin margins the pulled up to 2V through a 10k resistor, and the control output voltage over a continuous analog range of ±10%. voltage range is 0V to 1.5V. Tying this pin to GND adjusts output voltage by –10%.
SS (Pin D2):
The Soft-Start Pin. Place an external capacitor Driving this pin to 1.2V adjusts output voltage by 10%. A to ground to limit the regulated current during start-up voltage source or a voltage output DAC is ideal for driving conditions. The soft-start pin has an 11μA charging current. this pin. If the MARGA function is not used, either float this pin or terminate with a 1nF capacitor to GND.
RT (Pin E1):
The RT pin is used to program the switching frequency of the LTM8028’s buck regulator by connect-
TEST (Pin A8):
Factory Test. Leave this pin open. ing a resistor from this pin to ground. The Applications
SENSEP (Pin A9):
Kelvin Sense for VOUT. The SENSEP Information section of the data sheet includes a table pin is the inverting input to the error amplifier. Optimum to determine the resistance value based on the desired regulation is obtained when the SENSEP pin is connected switching frequency. When using the SYNC function, to the VOUT pins of the regulator. In critical applications, the set the frequency to be 20% lower than the SYNC pulse resistance of PCB traces between the regulator and the load frequency. Do not leave this pin open. can cause small voltage drops, creating a load regulation 8028fb For more information www.linear.com/LTM8028 7 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Package Photo Revision History Typical Application Related Parts