ADP1055ACPZ-R7 datasheet(32/140 Pages) AD

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ADP1055

Data Sheet

Rev. A | Page 32 of 140

AVERAGE CONSTANT CURRENT MODE

The ADP1055 supports constant current (CC) mode. The

constant current mode threshold is set in one of two ways:



Using the PMBus definition of CC mode (Register

0xFE4F[2] = 0)



Using the manufacturer specific CC mode (Register

0xFE4F[2] = 1)

In both modes, the constant current limit can be set as a

percentage of the IOUT_OC_FAULT_LIMIT—for example,

±3.125%, ±6.25%, ±12.5%, ±25%, ±50%, or ±100%—using

In the PMBus definition of CC mode, the constant current

mode is activated on a IOUT_OC_FAULT fault, and the load

current is limited to the CC limit, as specified in Register

0xFE5D[3:0]. Only positive percentages are applicable when the

PMBus definition of CC mode is used. The fault responses to

IOUT_OC_FAULT in this case are defined as per the PMBus

format. The system enters CC mode on detection of the CS2

current (~2.6 ms, 12-bit averaging of CS2 ADC). Any further

changes in the current while the device is in CC mode take

place according to the averaging speed selectable in Register

0xFE4F[7]. For CC mode to work properly using the PMBus

faults, the IOUT_OC_FAULT debounce must be set to 0 ms.

In the manufacturer specific CC mode, the CC limit is exactly

the limit that is programmed, and there is no need to trip the

IOUT_OC_FAULT before entering CC mode. Fault responses

to IOUT_OC_FAULT in this case are to ignore the fault or to

shut down the device in response to the fault (Register 0x47[7:6] =

11). Other settings programmed in the response section (for

example, Register 0x47[7:6] = 00, 01, or 10) are ignored.

Below the IOUT_OC_FAULT_LIMIT threshold, the ADP1055

operates in constant voltage mode, using the output voltage as

the feedback signal for closed-loop operation.

When the ADP1055 crosses the constant current mode threshold,

the CS2 current reading is used to control the output voltage

regulation point. The output voltage is ramped down linearly as

the load increases to ensure that the load current remains

constant.

Figure 51. Typical Characteristics in Constant Current (CC) Mode

The constant current control loop has relatively low bandwidth

because the current is averaged over a 328 μs period (9-bit

decimation of the CS2 bit stream). The output voltage changes

at a maximum rate of 1.18 V/sec at the VS± pins; therefore, the

instantaneous value of the current can exceed the constant

current limit for a very short period of time, depending on the

severity of the transient condition.

For a faster dynamic response of the constant current mode, the

turbo mode can be used. In turbo mode, the averaging time can

be decreased to a period of ~41 μs (6-bit decimation of the CS2

bit stream). In turbo mode, the slew rate of the output voltage

can be programmed using Register 0xFE5D[5:4].

As the output voltage is reduced to maintain a constant load

current, xxx_FAULT_RESPONSE (for example, Register

0x47[7:6] = 01) can be used to program a fault response when

the output voltage falls below a specific threshold set by

IOUT_OC_LV_LIMIT (Register 0x48).

It is important to note that although constant current mode can

be applied to any current fault (input or output current) according

to the PMBus specification, the ADP1055 applies the constant

current mode only to maintain a constant output current. For

example, if the IOUT_UC_FAULT is programmed to enter

constant current mode, the ADP1055 does not boost the output

voltage to maintain the current level set by IOUT_UC_LIMIT.

Using the manufacturer specific fault response for constant

current mode, the system can be forced into constant current

mode at a specific threshold, and if this threshold persists for a

specified amount of time (based on the debounce time), the

IOUT_OC_FAULT is tripped (see Figure 52).

Figure 52. Constant Current with Hiccup

32-BIT KEY CODE

The ADP1055 supports a 32-bit password (key code) in

addition to the EEPROM password set by Register 0xD5. This

32-bit key code enables another level of protection for the user

and the manufacturer to limit access to certain commands and

operations.

VOUT

IOUT

(0,0)

IOUT_OC_FAULT_LIMIT

VOUT NOMINAL

IOUT_OC_FAST

CC LIMIT

IOUT_OC_FAULT_LIMIT

TIME

IOUT NOMINAL

IOUT_OC_

DEBOUNCE

STARTS

IOUT_OC_

DEBOUNCE

STARTS

CONVERTER

STARTS

AFTER RETRY

ATTEMPT

IOUT_OC_DEBOUNCE

ENDS AND FAULT TRIPS

HICCUP

IOUT_OC_

DEBOUNCE

STARTS

DEPENDENT ON SLEW RATE

AND CC TURBO MODE

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