Features and Benefits
- Selectable light load operating modes of:
- Pulse-skipping (HV) and Burst Mode operation (LV)
- Burst Mode operation
- PLLIN pin to synchronize the LV regulators over a 1MHz to 3MHz range (166kHz to 500kHz for the HV converter)
- Watch dog circuit
- TEMP pin to monitor the junction temperature of the LTC3372
- PGOOD pin for the HV converter and RST pin for the LV regulators
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.