ADMC328YN datasheet(16/32 Pages) AD

16 / 32 page

ADMC328

–16–

REV. B

The second method for detecting a fault condition is through

the ISENSE pin in the analog block of the ADMC328. The ISENSE

pin monitors the feedback signals from a dc bus current sensing

resistor that represents the total current in the motor. When the

voltage of ISENSE goes below ISENSE trip threshold, PWMTRIP

will be internally pulled low. The negative edge of the internal

PWMTRIP will generate a shutdown in the same manner as a

negative edge on pin PWMTRIP.

It is possible through software to initiate a PWM shutdown by

writing to the 1-bit read/write PWMSWT register (0x2061).

Writing to this bit generates a PWM shutdown in a manner

identical to the PWMTRIP or ISENSE pins. Following a PWM

shutdown, it is possible to determine if the shutdown was gener-

ated from hardware or software by reading the same PWMSWT

Restarting the PWM after a fault condition is detected requires

clearing the fault and reinitializing the PWM. Clearing the fault

requires that PWMTRIP returns to a HI state and ISENSE returns

to a voltage greater than the ISENSE trip threshold. After the fault

has been cleared, the PWM can be restarted by writing to registers

PWMTM, PWMCHA, PWMCHB and PWMCHC. After the fault

is cleared and the PWM registers are initialized, internal timing

of the three-phase timing unit will resume, and the new duty cycle

values will be latched on the next rising edge of PWMSYNC.

PWM Registers

The configuration of the PWM registers is described at the end

of the data sheet. The parameters of the 16-bit PWM Timer is

tabulated in Table V.

ADC OVERVIEW

The ADC of the ADMC328 is based upon the single slope

conversion technique. This approach offers an inherently

monotonic conversion process and, to within the noise and sta-

bility of its components, there will be no missing codes.

Table VI. ADC Auxiliary Channel Selection

MODECTRL (1)

MODECTRL (0)

Select

ADCMUX1

ADCMUX0

VAUX0

VAUX1

VAUX2

Calibration (VREF)1

The single slope technique has been adapted on the ADMC328

for four channels that are simultaneously converted. Refer to

Figure 11 for the functional schematic of the ADC. Two of the

main inputs (V1 and V2) are directly connected as high imped-

ance voltage inputs. The third main input channel (ISENSE) has a

special design to monitor the voltage on a current-sensing resis-

tor whose voltage is always below (more negative than) GND. The

fourth channel has been configured with a serially-connected

4-to-1 multiplexer. Table VI shows the multiplexer input selection

codes. One of these auxiliary multiplexed channels is used to cali-

brate the ramp against the internal voltage reference (VREF).

VAUX0

V2L

VAUXL

PWMSYNC (CONVST)

ADC

REGISTERS

V1L

V3L

ISENSE

(CAP RESET)

CLK MODECTRL<7>

12-BIT

ADC

TIMER

BLOCK

PWMTRIP

VREF

COMP

ADC REGISTERS

ADC1

ADC2

ADC3

ADCAUX

MODECTRL<0..1>

EXTERNAL

CHARGING

CAP

ICONST

ICONST_TRIM<2:0>

VAUX1

VAUX2

COMP

–5 X

0.8 X

GND

4 – 1

MUX

Figure 11. ADC Overview

Comparing each ADC input to a reference ramp voltage, and tim-

ing the comparison of the two signals, performs the conversion

process. The actual conversion point is the time point intersec-

tion of the input voltage and the ramp voltage (VC) as shown in

Figure 12. This time is converted to counts by the 12-bit ADC

Timer Block and is stored in the ADC registers. The ramp volt-

age used to perform the conversion is generated by driving a

fixed current into an off-chip capacitor, where the capacitor

voltage is

VC = (I/C) × t

Table V. Fundamental Characteristics of PWM Generation Unit of ADMC328

16-BIT PWM TIMER

Parameter

Min

Typ

Max

Unit

Counter Resolution

Bits

Edge Resolution (Single Update Mode)

100

Edge Resolution (Double Update Mode)

Programmable Dead Time Range

100

µs

Programmable Dead Time Increments

100

Programmable Pulse Deletion Range

100

µs

Programmable Pulse Deletion Increments

100

PWM Frequency Range

150

PWMSYNC Pulsewidth (TCRST)

0.05

12.5

µs

Gate Drive Chop Frequency Range

0.02

MHz

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