RB1

RT1 + RB1

x

(RFB1 + RFB2)

RFB2

SM72442

SNVS689H – OCTOBER 2010 – REVISED APRIL 2013

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STARTUP

SM72442 has a soft start feature that will ramp its output voltage for a fixed time of 250ms.

If no output current is detected during soft-start time, the chip will then be in Panel Mode for 60 seconds. A

counter will start once the minimum output current threshold is met (set by ADC input channel 4). During these

60 seconds, any variation on the output power will not cause the chip to enter MPPT mode. Once 60 seconds

have elapsed, at a certain power level variation at the output (set by ADC input channel 2) will engage the chip in

MPPT mode.

If the output current exceeded the current threshold set at A/D Channel 6 (A6) during soft-start, the chip will then

engage in MPPT mode.

Figure 5. Startup Sequence

MAXIMUM OUTPUT VOLTAGE

Maximum output voltage on the SM72442 is set by resistor divider ratio on pin A0. (Please refer to Figure 2

Typical Application Circuit).

where

•

RT1 and RB1 are the resistor divider on the ADC pin A0

•

RFB1 and RFB2 are the output voltage sense resistors. A typical value for RFB2 is about 2 k

Ω

(1)

CURRENT LIMIT SETTING

Maximum output current can be set by changing the resistor divider on A4 (pin 18). Refer to Figure 2.

Overcurrent at the output is detected when the voltage on AIOUT (pin 21) equals the voltage on A4 (pin 18). The

voltage on A4 can be set by a resistor divider connected to 5V whereas the voltage on AIOUT can be set by a

current sense amplifier.

AVIN PIN

AVIN is an A/D input to sense the input voltage of the SM72442. A resistor divider can be used to scale max

voltage to about 4V, which is 80% of the full scale of the A/D input.

CONFIGURABLE SETTINGS

A/D pins A0, A2, A4, and A6 are used to configure the behavior of the SM72442 by adjusting the voltage applied

to them. One way to do this is through resistor dividers as shown in Figure 2, where RT1 to RT4 should be in the

range of 20 k

Ω.

8

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