as1720 austriamicrosystems, as1720 Datasheet - Page 6

• Manufacturer Part Number: as1720
• Description: Solenoid / Valve Driver With Current Limitation
• Manufacturer: austriamicrosystems

AS1720
Datasheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
Delay
The delay time is generated internally by a digital divider.
LDO and Reference Generator
This block provides the internal supply voltage of typ. 3.3V and all bias currents for the analog cells. Further the
external resistor divider for setting the duty cycle will be supplied.
Thermal shutdown
The temperature is constantly monitored. If the temperature exceeds typ. 160ºC the output is disabled. In order to exit
the over temperature condition, the device has to cool down and the reason of over temperature (e.g. short circuit)
must be removed. After exiting the overtemperature condition the system restarts beginning with the energising phase
followed by the hold phase.
DC Operation (AS1720A only)
After power up, the delay time
automatically. During the hold phase the DC output current is reduced according to the R
PWM Operation (AS1720B only)
After power up, the delay time
automatically. The internal RC oscillator sets the PWM period. The duty cycle is either defined by the external resistor
divider (voltage) at pin DUTY or by the fixed internal divider. When using the external divider the duty cycle can be
adjusted between 20% and 90% (e.g. from a DAC). Alternatively the pin can be driven by a voltage source. For using
the internal divider the pin DUTY has to be connected to V
to the internal divider, which causes a fixed 50% duty cycle.
Figure 9. Simplified Circuit of Block PWM and Control
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50% Duty cycle
adjustable
Duty cycle
fixed
(see Delay)
(see Delay)
R1
VDDA
R2
optional
DUTY
DUTYCYCLE V
VDDA
DUTY
starts running. After expiration of the delay the hold phase starts
starts running. After expiration of the delay the hold phase starts
V
ref
(
DUTY
Revision 1.03
Internal VDDA typ. 3.3V
R
)
PU
DDA
=
Off
On
VDDA
Oscillator
ENN
30kHz
0 381
. The comparator recognizes this condition and switches
,
PWM &
×
Control
V
DUTY
–
Delay
0 014
,
IH
on pin IH.
(EQ 1)
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