Data Sheet

LT83203/LT83205

analog.com

Rev. B

23 of 44

The current reference architecture of the LT83203/LT83205 allows remote sense of the negative terminals of the load

in addition to the positive terminal. Note the via on the ground side of the RSET and CSET going to the ground side of

the COUT, which can be configured for remote sense of the negative terminal of a load placed further away. For more

information on implementing remote sense for the LT83203/LT83205, see the Output Sensing and Stability section.

Forced Continuous Mode (FCM)

The LT83203/LT83205 can operate in FCM for fast transient response and full-frequency operation over a wide load

range. When in FCM, the oscillator operates continuously, and positive SW transitions are aligned to the clock.

Negative inductor current is allowed at light loads or under large transient conditions. In this mode, the

LT83203/LT83205 can sink current from the output and return this charge to the input, improving load-step transient

response (for a comparison of pulse-skipping mode and FCM, see Figure 50). At light loads, FCM operation is less

efficient than pulse-skipping operation, but it may be useful in applications where it is necessary to keep switching

harmonics out of the signal band. FCM must be used if the output is required to sink current. To enable FCM, connect

the pin to INTVCC or > 1.5V, or float the pin.

Figure 50. Load Step Transient Response with and without FCM

FCM is disabled under VIN overvoltage conditions (VIN pin is held above 18V), if VOUT is too high (PGFB pin is held greater

than 537.5mV) and during start-up until the voltage on VOUT has charged up to ~97.5% of its final value (as indicated

when the PGFB pin rises to above 486.5mV). For the latter two conditions, it is assumed the PGFB pin is connected to

the output voltage through an appropriate resistor divider. When FCM is disabled in these ways, negative inductor

current is not allowed, and the LT83203/LT83205 operates in pulse-skipping mode.

Pulse-Skipping Mode

When not operating in FCM, the LT83203/LT83205 operates in pulse-skipping mode. In this mode, the oscillator

operates continuously, and all switching cycles are aligned to the clock. The negative inductor current is not allowed

in this mode; therefore, at light loads, the LT83203/LT83205 may be operating in discontinuous mode. Additionally,

in pulse-skipping mode, the LT83203/LT83205 may also skip switching cycles at very light loads for improved

efficiency or at very high duty cycles to achieve better dropout. To enable pulse-skipping mode, connect the

SYNC/MODE pin to GND.

FORCED CONTINUOUS MODE

PULSE-SKIPPING MODE

0.1A

2.1A

20µs/DIV

ILOAD

2A/DIV

VOUT

20mV/DIV

VIN = 12V, VOUT = 1V, fSW = 2MHz, RC = 1.82kΩ, CC = 2.2nF

TYPICAL APPLICATION CIRCUIT