sx8725 Semtech Corporation, sx8725 Datasheet - Page 12

• Manufacturer Part Number: sx8725
• Description: Sx8725 Zoomingadc? For Pressure And Temperature Sensing
• Manufacturer: Semtech Corporation

SX8725
ZoomingADC™ for Pressure and Temperature Sensing
ADVANCED COMMUNICATIONS & SENSING
Charge Pump
This block generates a supply voltage able to power the analog switch drive levels on the chip.
The minimum acceptable switch supply is 3V which means that if V
drops below 3V then the block should
BATT
be activated to generate a voltage of 3V or above. If V
is greater than 3V then V
may be switched
BATT
BATT
straight through to the V
output.
PUMP
If control input bit MULT_FORCE_OFF = 1 in RegMode register then the charge pump is disabled and V
is
BATT
permanently connected to V
.
PUMP
If control input bit MULT_FORCE_ON = 1 in RegMode register then the charge pump is permanently enabled.
This overrides MULT_FORCE_OFF bit in RegMode register.
If MULT_FORCE_ON = 0 and MULT_FORCE_OFF = 0 bits in RegMode register then the charge pump will
start if V
drops below 3V, otherwise V
will be switched directly through to V
.
BATT
BATT
PUMP
These controls are supplied to give the user the option of fixing the charge pump state to avoid it turning off and
on when V
is close to 3V.
BATT
The cell will use the on-chip bandgap reference and comparator to detect when V
is too low. When
BATT
activated, the block will use the charge pump to boost the V
voltage to above 3V but with diode limiting to
BATT
ensure that the generated voltage never exceeds 0.7V above V
.
BATT
An external capacitor is required on V
whenever the power supply is supposed to be less or drop below 3V.
PUMP
This capacitor should be large enough to ensure that generated voltage is smooth enough to avoid affecting
conversion accuracy but not so large that it gives an unacceptable settling time. A recommended value is
around 2.2nF.
The block will also indicate when the pumped output voltage is sufficiently high to allow ADC conversions to be
started. This will be a simple comparison which will give a ready signal when the V
output is 3V or above.
PUMP
V1.5 © 2007 Semtech Corp.
www.semtech.com
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