Data Sheet AS8446

Revision 1.8, Date 2005-03-17

Page 27 of 35

Charge Pump and internal Oscillator

The charge pump is a one-stage pump that generates a pumped voltage Vpump about 10 V higher than the supply voltage Vbat

for Vbat > 13.5 V. It uses two external capacitors only, the capacitor Cp12 as the switched capacitor and Cp0 as the storage

capacitor.

The pumped voltage (Vpump - Vbat) is monitored to detect over or under voltages (protection of the power FET gate):

(Vpump - Vbat) = 10 V to 12 V : Normal voltage regulation of the charge pump

PARAMETER

SYMBOL

MIN

TYP

MAX

UNIT

NOTE

Pumped voltage

Vpump - Vbat

10

10.5

12

V

Vbat = 13.5 V, Iload = 5 mA

Pumped voltage

Vpump - Vbat

4.0

5.0

V

Vbat = 6.5 V, Iload = 2.5 mA

Pumped voltage

Vpump - Vbat

4.0

V

6.0V

≤ Vbat < 6.5V (low-Battery-

mode), Iload = 250µA

Under voltage threshold

(VPUMP_MIN = 1)

5.4

6.0

6.6

V

falling (Vpok)

Under voltage threshold

(VPUMP_MIN = 0)

3.4

4.0

4.6

V

falling (Vpok)

regulated voltage

threshold

10

10.5

12

V

rising

frequency

40

50

70

kHz

Motor Current Measurement Unit / Over Current Detection

high side motor line. The chip has two measurement amplification channels with separately programmable amplification factors

In general, all programming possibilities can be used to build up a measurement system within the defined limits.

factor caused by offset.

The programming of theses two amplification channels is usually realized in a way that the measurement range of the over

current measurement channel is wider than the normal current measurement channel.

In the whole system the analogue outputs A_current and A_overc are used via an ADC in the controlling

µP to regulate and

control the system. There is one exception only: The over current detection and protection is realized directly by the over

current measurement channel to be able to act very fast in case of an over current situation (short circuit).

The measurement unit contains a low pass filter to prevent wrong measurement if short transients of the measurement input

voltage occurs (cut-off frequency about 500 kHz).

The motor current measurement unit is endowed with an auto calibration procedure for the offset voltage. The motor current

respectively the measurement voltage (Vcmp - Vcmn) must be zero during this calibration.

This calibration is done after the start up of the system including the ready signal of the charge pump: power on reset signal

nPOR and Vpok = high starts the calibration. The calibration procedure needs about 200

µs.