ADP1055ACPZ-R7 datasheet(22/140 Pages) AD

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ADP1055

Data Sheet

Rev. A | Page 22 of 140

MODULATION LIMIT

The modulation limit register (Register 0xFE53) can be

programmed to apply a maximum duty cycle modulation limit

to any PWM signal, thus acting as a clamp for the maximum

modulation range of any PWM output. When modulation is

enabled, the maximum modulation limit is applied to all PWM

outputs collectively. As shown in Figure 26, this limit is the

maximum time variation for the modulated edges from the

default timing, following the configured modulation direction.

Figure 26. Modulation Limit Settings

There is no minimum duty cycle limit setting. Therefore, the

user must set the rising edges and falling edges based on the

case with the least modulation to enter pulse skipping mode

under very light load conditions.

Each LSB in Register 0xFE53[6:0] corresponds to a unit of a

base time step size. The base time step size (20 ns, 40 ns, 80 ns,

or 160 ns) depends on the switching frequency; therefore, the

modulation limit is based on the value in Register 0xFE53[6:0]

multiplied by the corresponding base time step size. The

modulated edges are prevented from extending beyond one

switching cycle, but the maximum duty cycle is 100% (the

minimum pulse width is 5 ns).

The GUI provided with the ADP1055 is recommended for

programming this feature (see Figure 27).

Figure 27. Setting Modulation Limits (Modulation Range Shown by Arrows)

SWITCHING FREQUENCY PROGRAMMING

The FREQUENCY_SWITCH command (Register 0x33) sets

the switching frequency of the ADP1055 in kilohertz. This

command has two data bytes formatted in the linear data format;

the programmable frequency ranges from 48 kHz to 1000 kHz.

The ADP1055 does not support every possible frequency due to

the infinite combinations of exponent and mantissa values that

can be programmed. If a programmed frequency does not exactly

match a supported value, it is rounded up to the nearest available

frequency. It is recommended that the READ_FREQUENCY

command (Register 0x95) be used to determine the exact value

of the switching frequency. Table 244 lists the supported

frequencies.

OUTx

tMODULATION_LIMIT

tRX

tFX

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