AAT2601 Datasheet, PDF (27/38 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

PRODUCT DATASHEET
AAT2601178
Total Power Solution for Portable Applications
Next, the power dissipation for the charger can be cal-
culated by the following equation:
P_D = (V_CHGIN - V_BAT) · I_{CH_CC} + (V_CHGIN · I_OP) + (V_CHGIN - V_SYSOUT) · I_SYSOUT
+ (V_SYSOUT - V_OUT1) · I_OUT1 + (V_SYSOUT - V_OUT2) · I_OUT2
+ (V_SYSOUT - V_OUT3) · I_OUT3 + (V_SYSOUT - V_OUT4) · I_OUT4
+ (V_SYSOUT - V_OUT5) · I_OUT5
+
⎛
I²
OUTBUCK
·
⎝^RDS(ON)L
·
V_OUTBUCK
V_SYSOUT
+
R_DS(ON)H
· [V_SYSOUT -
V_SYSOUT
V_OUTBUCK]⎞
⎠
Where:
P_D = Total Power Dissipation by the Device
V_CHGIN = CHGIN Input Voltage
V_BAT = Battery Voltage at the BAT Pin
I_{CH_CC} = Constant Charge Current Programmed for the
Application
I_OP = Quiescent Current Consumed by the IC for Normal
Operation [0.5mA]
V_SYSOUT and I_SYSOUT = Output voltage and load current
from the SYSOUT pin for the system LDOs and step-
down converter [3.9V out for SYSOUT]
R_DS(ON)H and R_DS(ON)L = On-resistance of step-down high
and low side MOSFETs [0.8Ω each]
V_OUTX and I_OUTX = 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 (T_REG =
100°C, Thermal Loop Regulation). The maximum charge
current is the key factor when designing battery charger
applications.
⎛(T_REG - T_A)
⎝
I = _{CH_CC(MAX)}
θ_JA
- (V_CHGIN · I_OP)^⎞⎠ - (V_CHGIN - V_SYSOUT) · I_SYSOUT)
- [(V_SYSOUT - V_OUT1) · I_OUT1] - (V_SYSOUT - V_OUT2) · I_OUT2
- [(V_SYSOUT - V_OUT3) · I_OUT3] - (V_SYSOUT - V_OUT4) · I_OUT4
- (V_SYSOUT - V_OUT5) · I_OUT5
-
I²
OUTBUCK
·
⎛⎝_RDS(ON)L
·
V_OUTBUCK
V_SYSOUT
+
R_DS(ON)H · (V_SYSOUT - V_OUTBUCK)⎞
V_SYSOUT
⎠
V_CHGIN - V_BAT
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 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.
For the above example at T_A = 30°C, the I_{CH_CC(MAX)} =
546mA.
Thermal Overload Protection
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).
Synchronous Step-Down
Converter (Buck)
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 (C_IN, C_OUT, 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 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.
2601.2008.01.1.0
www.analogictech.com
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