Demonstration circuit 2419A features the LTC3372 in a
multi-output step-down converter. The controller portion
of the LTC3372 drives a high output voltage (HV) buck
converter which has an input voltage range of 6V to 60V.
Its output voltage (VOUT_HV) is nominally 5V but can be
configured for either 5V or 3.3V with the VOUTPRG pin.
VOUT_HV supplies power to the configurable buck regulator.
This regulator provides four low voltage (LV) outputs
labelled VOUT1-4. These outputs are 1.2V/2A, 1.8V/2A,
2.5V/2A and 3.3V/2A respectively. When VOUT_HV is configured
for 5V, it can supply 6A to the external loads with
full load on VOUT1-4. With no load on VOUT1-4, VOUT_HV
can supply 10A to the external loads.
The LV buck regulator consists of eight power stages that
can be arranged in up to four channels. The LV regulator
on the DC2419A is setup for four channels of two power
stages each. With modifications, the LV buck regulator
can be setup for eight different configurations.
If VOUT_HV is programmed for 3.3V, then VOUT4 which
provides 3.3V/2A will be in dropout. This rail will require
an external input voltage to stay in regulation.
The LV rails operate at 2MHz and the HV converter operates
at one-sixth this frequency or 333kHz. The high frequency
of the LV rails allows the use of 4mm × 4mm
inductors. The power stage for the HV converter consists
of 60V avalanche rated MOSFETs and a 2.2μH 10mm ×
10mm inductor. A 4mΩ discrete sense resistor is used
to sense current.
The low IQ current of the LTC3372 provides high efficiency
at light loads. When the VOUT_HV is supplying the nominal
5V, its Burst Mode® efficiency with 1mA load is 90.3% for
a 12V input. When the HV converter is off,
it only draws 27μA from a 12V input.
The LTC3372 data sheet provides a complete description
of the IC operation and application information. The data
sheet must be read in conjunction with the quick start
guide.
