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AAT3603 Datasheet, PDF (27/35 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications
PRODUCT DATASHEET
AAT3603178
Total Power Solution for Portable Applications
Next, the power dissipation for the charger can be cal-
culated by the following equation:
PD = (VCHGIN - VBAT) · ICH_CC + (VCHGIN · IOP) + (VCHGIN - VBAT) · IBAT
+ (VBAT - VOUT1) · IOUT1 + (VBAT - VOUT2) · IOUT2
+ (VBAT - VOUT3) · IOUT3 + (VBAT - VOUT4) · IOUT4
+ (VBAT - VOUT5) · IOUT5
+
IOUTBUCK2 ·
RDS(ON)L ·
VOUTBUCK
VBAT
+
RDS(ON)H · [VBAT - VOUTBUCK]
VBAT
Where:
PD = Total Power Dissipation by the Device
VCHGIN = CHGIN Input Voltage
VBAT = Battery Voltage at the BAT Pin
ICH_CC = Constant Charge Current Programmed for the
Application
IOP = Quiescent Current Consumed by the IC for Normal
Operation [0.5mA]
VBAT = Load current from the BAT pin for the system
LDOs and step-down converter
RDS(ON)H and RDS(ON)L = On-resistance of step-down high
and low side MOSFETs [0.8Ω each]
VOUTX and IOUTX = Output voltage and load currents for
the LDOs and step-down converter [3V out for each
LDO]
By substitution, we can derive the maximum charge cur-
rent before reaching the thermal limit condition (TREG =
100°C, Thermal Loop Regulation). The maximum charge
current is the key factor when designing battery charger
applications.
I = CH_CC(MAX)
(TREG - TA)
θJA
- (VCHGIN · IOP)
- (VCHGIN - VBAT) · IBAT
- [(VBAT - VOUT1) · IOUT1] - (VBAT - VOUT2) · IOUT2
- [(VBAT - VOUT3) · IOUT3] - (VBAT - VOUT4) · IOUT4
- (VBAT - VOUT5) · IOUT5
-
I2
OUTBUCK
·
RDS(ON)L
·
VOUTBUCK
VBAT
+
RDS(ON)H · (VBAT - VOUTBUCK)
VBAT
VCHGIN - VBAT
In general, the worst condition is when there is the
greatest voltage drop across the charger, when battery
voltage is charged up to just past the preconditioning
voltage threshold and the LDOs and step-down con-
verter are sourcing full output current.
For example, if 977mA is being sourced from the BAT pin
to the LDOs and Buck channels (300mA to LDO1, 100mA
to LDO2-5, and 277mA to the Buck; see buck efficiency
graph for 300mA output current) with a CHGIN supply of
5V, and the battery is being charged at 3.0V with 800mA
charge current, then the power dissipated will be 3.64W.
A reduction in the charge current (through I2C) may be
necessary in addition to the reduction provided by the
internal thermal loop of the charger itself.
For the above example at TA = 30°C, the ICH_CC(MAX) =
386mA.
Thermal Overload Protection
The AAT3603 integrates thermal overload protection
circuitry to prevent damage resulting from excessive
thermal stress that may be encountered under fault con-
ditions, for example. This circuitry disables all regulators
if the AAT3603 die temperature exceeds 140°C, and
prevents the regulators from being enable until the die
temperature drops by 15°C (typ).
Synchronous Step-Down
Converter (Buck)
The AAT3603 contains a high performance 300mA,
1.5MHz synchronous step-down converter. The step-
down converter operates to ensure high efficiency per-
formance over all load conditions. It requires only three
external power components (CIN, COUT, and L). A high DC
gain error amplifier with internal compensation controls
the output. It provides excellent transient response and
load/line regulation. Transient response time is typically
less than 20μs. The converter has soft start control to
limit inrush current and transitions to 100% duty cycle
at drop out.
The step-down converter input pin PVIN should be con-
nected to the BAT output pin. The output voltage is
internally fixed at 1.8V. Power devices are sized for
300mA current capability while maintaining over 90%
efficiency at full load.
3603.2008.06.1.0
www.analogictech.com
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