MAX17843 datasheet(45/131 Pages) MAXIM

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HV Charge Pump

The high-voltage multiplexers must be powered by a sup-

ply higher than any monitored voltage. To this end, an

internal charge pump draws power from the DCIN input

to provide a high-voltage supply (VHV) that is regulated to

VDCIN + 5.5V (nominal). When the charge pump achieves

regulation, charge pumping stops until the voltage drops

by 20mV. The charge pump is automatically disabled

during shutdown and during the measurement cycle to

eliminate charge-pump noise. The charge pump can also

be disabled manually by setting the HVCPDIS bit in the

DEVCFG2 register.

If VHV–VDCIN drops below VHVUV, the HV undervoltage

flag (ALRTHVUV) is set. If VHV drops too low relative to

the C12 input, there is insufficient headroom to guarantee

that HVMUX switch resistance is sufficiently low for an

accurate acquisition of the channel. To properly identify

this fault condition, if VHV–VC12 is too low during the

acquisition, the HV headroom-alert flag (ALRTHVHDRM)

is set in the FMEA2 register. The HV undervoltage and

HV headroom-alert functions can be verified by disabling

the HV charge pump (HVCPDIS = 1) and allowing VHV

to decay while in acquisition mode. An overvoltage com-

parator disables the charge pump in the case where VHV–

VDCIN exceeds 8.5V. This condition is indicated by the

ALRTHVOV bit in the FMEA2 register. The ALRTHVOV

alert does not necessarily indicate a condition that affects

measurement accuracy. HV charge-pump diagnostics are

summarized in Table 18.

Table 18. HV Charge-Pump Diagnostics

Figure 22. HV Charge Pump

FAULT

CONDITION

ALERT BIT

LOCATION

VHV undervoltage

VHV–VDCIN < VHVUV

ALRTHVUV

FMEA1[3]

VHV overvoltage

VHV–VDCIN > VHVOV

ALRTHVOV

FMEA2[0]

VHV low headroom

VHV–VC12 < VHVHDRM (min.)

ALRTHVHDRM

FMEA2[2]

MAX17843

CDCIN

CCP

15MA

CHV

SWITCH

LOGIC

5.5V

RDCIN

20MV

HYST.

INTERNAL POR/

TO ALRTHVUV

4.1V

32KHZ

MEASURING

DISABLE

DEVCFG2.

HVCPDIS

DISABLE

HVOV

TO ALRTHVOV

HVOV

8.5V

RHV

CPP

DCIN

CPN

AGND

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

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