ATA5279-PLQW Atmel, ATA5279-PLQW Datasheet - Page 7

• Manufacturer Part Number: ATA5279-PLQW
• Description: RF Wireless Misc High-end multiple antenna driver IC
• Manufacturer: Atmel

Specifications of ATA5279-PLQW

• Package / Case: VQFN-48
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3.4
3.5
9125L–RKE–03/11
Boost Converter
Coil Current Sensing (Zero Cross, Sample and Hold, Integrator)
In application, the output coil current is the fixed valued (selectable via SPI). Hence, the
required output voltage is calculated as follows:
Here, Z
appropriate return line current selector (see also
32) and R
see also
The coil driver stage can be supplied by a DC-DC converter in boost configuration. Together
with an externally applied choke, freewheeling diode and capacitor, the battery voltage can be
brought up to the required value, which is dependant on the coil's impedance and the selected
current. The converter is only enabled during an active transmission. The peak current
through the low-side switch I
converter operation in case one of the values exceeds its upper limit.
Note:
The switching frequency is, like the coil driving signal, derived from the oscillator stage and
125kHz in value when using an 8MHz input clock. The least possible time the boost converter
takes to generate the maximum possible output voltage from the minimum possible input volt-
age is dependant on several parameters. The values of the external components (choke
inductance, charge capacitance and CINT integration capacitance) greatly effects this time.
The coil current flows through an external shunt resistor, causing a current-dependant voltage,
which is fed into the IC via the VSHS pin. By monitoring the zero crossing events of this signal,
the phase of the coil current is known and hence the positive peak value can be sampled.
The peak coil current is then subtracted from an internal reference voltage that is dependant
on the selected coil current, which results in the regulation difference.
An amplifier stage converts this difference into a current, which is then fed into an externally
applied integration capacitor connected to the CINT pin. The resulting voltage on this capaci-
tor directly influences the amplitude of the sine wave signal. It also determines the supply
voltage generated by the boost converter, if the necessary coil supply voltage exceeds the
actual supply voltage level. Note that during an active transmission, this voltage is internally
limited to V
Note that in idle mode, the voltage on the integration capacitor is kept at a value that corre-
sponds to the battery supply voltage. This ensures that the boost converter, if needed, always
performs a soft start from the battery voltage level on.
The desired current can be selected via the SPI. A total of 20 predefined steps are available,
divided into the following sections:
V
Out,p
• The lower four steps (50mA to 200mA) are intended for the low-current coils only
• The next ten steps (250mA to 700mA) are intended for both types of coils
• The upper six steps (750mA to 1A) are intended only for the high-current coils
=
Coil
There is no dedicated temperature monitoring for the boost converter low-side switch. For fur-
ther details, please refer to
I
Section 4. “Application” on page
Coil,p
Shunt
CINT,max
is the complex impedance of the coil, R
is the resistance of the externally applied current sense shunt resistor (typ. 1 ,
Z
.
Coil
+
R
DSon,HRS/LRS
VL
and the output voltage V
Section 4.1 “Application Hints” on page
+
R
Shunt
27).
Section 8. “Functional Parameters” on page
DSon,HRS/LRS
VDS
are measured to shut down the
Atmel ATA5279
is the on-resistance of the
28.
7