LTC4090EDJC#PBF Linear Technology, LTC4090EDJC#PBF Datasheet - Page 18

• Manufacturer Part Number: LTC4090EDJC#PBF
• Description: IC USB POWER MANAGER 22-DFN
• Manufacturer: Linear Technology

Specifications of LTC4090EDJC#PBF

• Function: Power Management
• Battery Type: Lithium-Ion (Li-Ion), Lithium-Polymer (Li-Pol)
• Voltage - Supply: 4.35 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 22-WFDFN Exposed Pad
• Supply Voltage Range: 4.35V To 5.5V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: DFN
• No. Of Pins: 22
• Msl: MSL 1 - Unlimited
• Termination Type: SMD
• Supply Voltage Min: 4.35V
• Rohs Compliant: Yes
• Filter Terminals: SMD
• Frequency: 2.7MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC4090/LTC4090-5
APPLICATIONS INFORMATION
USB and 5V Wall Adapter Power
Although the LTC4090/LTC4090-5 are designed to draw
power from a USB port, a higher power 5V wall adapter
can also be used to power the application and charge the
battery (higher voltage wall adapters can be connected
directly to HVIN). Figure 4 shows an example of combining
a 5V wall adapter and a USB power input. With its gate
grounded by 1k, P-channel MOSFET MP1 provides USB
power to the LTC4090/LTC4090-5 when 5V wall power is
not available. When 5V wall power is available, diode D1
supplies power to the LTC4090/LTC4090-5, pulls the gate
of MN1 high to increase the charge current (by increasing
the input current limit), and pulls the gate of MP1 high to
disable it and prevent conduction back to the USB port.
Setting the Switching Frequency
The high voltage switching regulator uses a constant-
frequency PWM architecture that can be programmed to
switch from 200kHz to 2.4MHz by using a resistor tied
from the R
R
Table 1. Switching Frequency vs R
18
T
SWITCHING FREQUENCY (MHz)
value for a desired switching frequency is in Table 1.
T
pin to ground. A table showing the necessary
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
T
Value
R
T
VALUE (kΩ)
88.7
68.1
56.2
46.4
40.2
34.0
29.4
23.7
19.1
16.2
13.3
11.5
9.76
8.66
187
121
Operating Frequency Trade-Offs
Selection of the operating frequency for the high voltage
buck regulator is a trade-off between effi ciency, compo-
nent size, minimum dropout voltage, and maximum input
voltage. The advantage of high frequency operation is that
smaller inductor and capacitor values may be used. The
disadvantages are lower effi ciency, lower maximum input
voltage, and higher dropout voltage. The highest acceptable
switching frequency (f
be calculated as follows:
where V
V
is the catch diode drop (~0.5V), and V
switch drop (~0.5V at max load). This equation shows
that slower switching frequency is necessary to safely
accommodate high V
the next section, lower frequency allows a lower dropout
voltage. The reason input voltage range depends on the
switching frequency is because the high voltage switch
has fi nite minimum on and off times. The switch can turn
on for a minimum of ~150ns and turn off for a minimum
of ~150ns. This means that the minimum and maximum
duty cycles are:
where f
minimum switch-on time (~150ns), and t
USB POWER
850mA I
500mA I
HVOUT
ADAPTER
5V WALL
DC
DC
f
SW(MAX)
MIN
MAX
CHG
CHG
is the output voltage of the switching regulator, V
SW
HVIN
= f
= 1 – f
Figure 4. USB or 5V Wall Adapter Power
is the switching frequency, t
MP1
SW
=
1k
is the typical high voltage input voltage,
t
ON(MIN)
• t
SW
ON(MIN)
• t
D1
HVIN
SW(MAX)
OFF(MIN)
V
• V
MN1
IN
D
(
/V
+ V
D
HVOUT
LTC4090
+ V
2.87k
HVOUT
) for a given application can
CLPROG
HVIN
PROG
ratio. Also, as shown in
BAT
– V
SW
SW
2k
ON(MIN)
OFF(MIN)
is the internal
)
I
CHG
59k
4090 F04
+
Li-Ion
BATTERY
is the
is the
4090fc
D