LTC3557EUF#PBF Linear Technology, LTC3557EUF#PBF Datasheet - Page 22

• Manufacturer Part Number: LTC3557EUF#PBF
• Description: IC USB POWER MANAGE 28-QFN
• Manufacturer: Linear Technology

Specifications of LTC3557EUF#PBF

• Applications: Handheld/Mobile Devices
• Voltage - Supply: 4.35 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-QFN
• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Pin Count: 28
• Mounting: Surface Mount
• Package Type: QFN EP
• Case Length: 4mm
• Screening Level: Industrial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -
• Lead Free Status / Rohs Status: Compliant

LTC3557/LTC3557-1
APPLICATIONS INFORMATION
22
Figure 7. LTC3557-1V
with the LT3505
Figure 6. LTC3557 V
with the LT3480
5.0
4.5
4.0
3.5
3.0
2.5
5.0
4.5
4.0
3.5
3.0
2.5
2.5
2.5
8V TO 36V
3
3
Figure 5. LT3505 Buck Control Using V
HV
OUT
OUT
IN
BAT (V)
BAT (V)
Voltage vs Battery Voltage
3.5
3.5
Voltage vs Battery Voltage
1μF
BUCK CIRCUITRY
HIGH VOLTAGE
LT3505
4
4
I
I
I
BAT
O
O
O
I
I
BAT
68nF
20k
O
O
= 0.0A
= 0.75A
= 1.5A
= 0.0A
= 0.6A
35571 F07
35571 F06
806k
4.5
BZT52C16T
4.5
150k
3
4
6
V
SHDN
R
GND
IN
T
LT3505
5, 9
C
BOOST
(2.2MHz Switching with Frequency Foldback)
V
V
SW
C
C
8
26
FB
LTC3557-1
WALL ACPR
LTC3557
This technique provides a signifi cant effi ciency advantage
over the use of a 5V buck to drive the battery charger. With
a simple 5V buck output driving V
effi ciency is approximately:
where η
regulator and 5V is the output voltage of the buck regulator.
With a typical buck effi ciency of 87% and a typical battery
voltage of 3.8V, the total battery charger effi ciency is
approximately 66%. Assuming a 1A charge current, this
works out to nearly 2W of power dissipation just to charge
the battery!
With the V
is approximately:
With the same assumptions as above, the total battery
charger effi ciency is approximately 81%. This example
works out to just 900mW of power dissipation. For
applications, component selection and board layout
information beyond those listed here please refer to the
respective LT3480, LT3481 or LT3505 data sheet.
1
2
7
3
η
η
0.1μF
CHARGER
CHARGER
25
MBRM140
V
GATE
BAT
OUT
BUCK
6.8μH
C
23
21
22
control technique, battery charger effi ciency
1N4148
= η
= η
is the effi ciency of the high voltage buck
49.9k
10.0k
Si2333DS
BUCK
BUCK
10μF
•
•
0.3V + V
V
+
5V
BAT
Si2333DS
(OPT)
35571 F05
Li-Ion
V
UP TO
1.2A
BAT
C
OUT
BAT
V
BAT
OUT
OUT
, battery charger
35571fc