参数资料
型号: LTC3554EPD#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 0.6 A BATTERY CHARGE CONTROLLER, 2590 kHz SWITCHING FREQ-MAX, PQCC20
封装: 3 X 3 MM, LEAD FREE, PLASTIC, UTQFN-20
文件页数: 25/36页
文件大小: 418K
代理商: LTC3554EPD#TRPBF
LTC3554/LTC3554-2
31
35542fb
Holding ON low through the one second power-down
period will not cause a power-up event at end of the one
second period. ON must be brought high following the
power-down event and then go low again for 400ms to
establish a valid power-up event, as shown in Figure 12.
The regulators in Figure 13 are slewing up with nominal
output capacitors and no-load. Adding a load or increas-
ing output capacitance on any of the outputs will reduce
the slew rate and lengthen the time it takes the regulator
to get into regulation.
OPERATION
BAT
VBUS
ON (PB)
PBSTAT
BUCK1
BUCK2
PGOOD
PWR_ON1
PWR_ON2
STATE
PON
PUP1
HR
PDN1
3554 TD06
400ms
50ms
tON_HR
1s
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
VOUT2
0.5V/DIV
VOUT1
1V/DIV
0V
3554 F13
100μs/DIV
Figure 13. Power-Up Sequencing
Figure 12. Hard Reset Via Holding ON Low
LAYOUT AND THERMAL CONSIDERATIONS
Printed Circuit Board Power Dissipation
In order to be able to deliver maximum charge current
under all conditions, it is critical that the Exposed Pad
on the backside of the LTC3554 package is soldered
to a ground plane on the board. Correctly soldered to a
2500mm2 ground plane on a double-sided 1oz copper
board, the LTC3554 has a thermal resistance (
θJA) of
approximately 70°C/W. Failure to make good thermal
contact between the Exposed Pad on the backside of the
package and an adequately sized ground plane will result
in thermal resistances far greater than 70°C/W.
The conditions that cause the LTC3554 to reduce charge
current due to the thermal protection feedback can be
approximated by considering the power dissipated in the
part. For high charge currents the LTC3554 power dis-
sipation is approximately:
PD = (VBUS–BAT) IBAT + PD(REGS)
where PD is the total power dissipated, VBUS is the supply
voltage, BAT is the battery voltage, and IBAT is the battery
charge current. PD(REGS) is the sum of power dissipated
on chip by the step-down switching regulators.
Power-Up Sequencing
Figure 13 shows the actual power-up sequencing of the
LTC3554. Buck1 and buck2 are both initially disabled (0V).
Once the pushbutton has been applied (ON low) for 400ms
buck1 is enabled. Buck1 slews up and enters regulation.
The actual slew rate is controlled by the soft start func-
tion of buck1 in conjunction with output capacitance and
load (see the Step-Down Switching Regulator Operation
section for more information). When buck1 is within about
8% of nal regulation, buck2 is enabled and slews up
into regulation. 230ms after buck2 is within 8% of nal
regulation, the PGOOD output will go high impedance.
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