PRODUCT DATASHEET
AAT2601178
Total Power Solution for Portable Applications
Next, the power dissipation for the charger can be cal-
culated by the following equation:
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.
PD = (VCHGIN - VBAT) · ICH_CC + (VCHGIN · IOP) + (VCHGIN - VSYSOUT) · ISYSOUT
+ (VSYSOUT - VOUT1) · IOUT1 + (VSYSOUT - VOUT2) · IOUT2
+ (VSYSOUT - VOUT3) · IOUT3 + (VSYSOUT - VOUT4) · IOUT4
+ (VSYSOUT - VOUT5) · IOUT5
For example, if 913mA is being sourced from the 3.9V
SYSOUT pin to the LDOs and Buck channels (300mA to
LDO1, 100mA to LDO2-5, and 213mA 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 dissi-
pated will be 3.32W. A reduction in the charge current
(through I2C) may be necessary in addition to the reduc-
tion provided by the internal thermal loop of the charger
itself.
VOUTBUCK
VSYSOUT
RDS(ON)H · [VSYSOUT - VOUTBUCK
]
⎞
⎠
⎛
⎝
2
+ IOUTBUCK · RDS(ON)L
·
+
VSYSOUT
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
For the above example at TA = 30°C, the ICH_CC(MAX)
546mA.
=
IOP = Quiescent Current Consumed by the IC for Normal
Operation [0.5mA]
Thermal Overload Protection
VSYSOUT and ISYSOUT = Output voltage and load current
from the SYSOUT pin for the system LDOs and step-
down converter [3.9V out for SYSOUT]
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]
The AAT2601 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 AAT2601 die temperature exceeds 140°C, and
prevents the regulators from being enable until the die
temperature drops by 15°C (typ).
By substitution, we can derive the maximum charge cur-
Synchronous Step-Down
Converter (Buck)
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.
The AAT2601 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.
⎛
⎝
⎞
⎠
(TREG - TA)
- (VCHGIN · IOP) - (VCHGIN - VSYSOUT) · ISYSOUT
)
θJA
ICH_CC(MAX)
=
- [(VSYSOUT - VOUT1) · IOUT1] - (VSYSOUT - VOUT2) · IOUT2
- [(VSYSOUT - VOUT3) · IOUT3] - (VSYSOUT - VOUT4) · IOUT4
- (VSYSOUT - VOUT5) · IOUT5
The step-down converter input pin PVIN should be con-
nected to the SYSOUT LDO output pin. The output volt-
age is internally fixed at 1.8V. Power devices are sized
for 300mA current capability while maintaining over
90% efficiency at full load.
VOUTBUCK
RDS(ON)H · (VSYSOUT - VOUTBUCK)
⎞
⎛
- IOUTBUCK2 · RDS(ON)L
·
+
VSYSOUT
⎠
VSYSOUT
⎝
VCHGIN - VBAT
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2601.2008.01.1.0
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