ADP1043A datasheet(25/72 Pages) AD

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ADP1043A

Rev. 0 | Page 25 of 72

CONSTANT CURRENT MODE

The ADP1043A can be configured to operate in constant

current mode. The threshold to enter constant current mode

operation is 10% current below the CS2 accurate OCP setting.

Below this current, the part operates normally, using the output

voltage as the feedback signal for closed-loop operation.

When the ADP1043A reaches the constant current mode

threshold, a flag is set. The CS2 current reading is used instead

of the output voltage as the feedback signal for closed-loop

operation. The output voltage is ramped down linearly to 60%

of its nominal value as the load resistance decreases to ensure

that the current remains constant.

When the control loop reaches 60% of VOUT, the part again uses

the output voltage to close the loop, but at the reduced level

(60% of nominal). If the load resistance continues to decrease,

the current may rise again in this region, up to the CS2 OCP

level, but the voltage is kept limited to 60% of nominal (see

Figure 30). The UVP or CS2 OCP flags can be used to program

a shutdown action.

VOUT NOMINAL

VOUT × 60%

VOUT

IOUT

OCP

OCP × 90%

Figure 30. Constant Current Mode (VOUT vs. IOUT)

OVERVOLTAGE PROTECTION (OVP)

The ADP1043A has two OVP circuits. If the output voltage at

the VS1, VS2, or VS3 pin exceeds the programmable threshold

for that pin, that OVP flag is set; the response to that flag can be

programmed. VS1 has one OVP circuit. VS2 and VS3 share the

other OVP circuit. The OVP circuits can be programmed for

different OVP thresholds. See Register 0x32 and Register 0x33

for more information. The formula to set the OVP threshold

voltage is given by

VSx OVP

= [(89 + VS1_OVP_Setting)/128] × 1.55 V

For example, when the VS1 OVP setting = 10, then

VS1 OVP

= [(89 + 10)/128] × 1.55 V = 1.2 V

UNDERVOLTAGE PROTECTION (UVP)

If the voltage being sensed at the VS1 pin goes below the pro-

grammable UVP threshold, the UVP flag is set. Exceptions

to this rule (called undervoltage blanking) include during

startup and when ACSNS is not within limits. The response

to the UVP condition is programmable (see Register 0x34 in

Table 48 for more information).

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