LTC1473LCGN Linear Technology, LTC1473LCGN Datasheet - Page 7

• Manufacturer Part Number: LTC1473LCGN
• Description: IC SWITCH DVR PWRPATH DUAL16SSOP
• Manufacturer: Linear Technology
• Series: PowerPath™r

Specifications of LTC1473LCGN

• Applications: Handheld/Mobile Devices
• Fet Type: N-Channel
• Number Of Outputs: 2
• Internal Switch(s): No
• Delay Time - On: 22µs
• Delay Time - Off: 1µs
• Voltage - Supply: 2.8 V ~ 9 V
• Current - Supply: 100µA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Power Switch Family: LTC1473L
• Mounting: Surface Mount
• Supply Current: 100uA
• Package Type: SSOP N
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Pin Count: 16
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

OPERATIO
The LTC1473L is responsible for low-loss switching and
isolation for a dual supply system, where during a power
backup situation, a battery pack can be connected or
disconnected seamlessly. Smooth switching between in-
put power sources is accomplished with the help of
low-loss N-channel switches. They are driven by special
gate drive circuitry which limits the inrush current in and
out of the battery packs and the system power supply
capacitors.
All N-Channel Switching
The LTC1473L drives external back-to-back N-channel
MOSFET switches to direct power from two sources: the
primary battery and the secondary battery, or a battery and
a DC power supply. (N-channel MOSFET switches are
more cost effective and provide lower voltage drops than
their P-channel counterparts.)
Gate Drive (V
The gate drive for the low-loss N-channel switches is
supplied by an internal micropower boost regulator which
is regulated at approximately 8.5V above V
maximum. In a DC supply and backup battery system, the
LTC1473L V
Schottky diodes connected to the two main power sources,
DCIN and BAT1. Thus, V
higher power source and will provide the overdrive
required to fully enhance the MOSFET switches.
For maximum efficiency the input to the boost regulator
inductor is connected to V
provides filtering to the input of the 1mH switched induc-
tor, L1, which is housed in a small surface mount package.
An internal diode directs the current from the 1mH induc-
tor to the V
Inrush and Short-Circuit Current Limiting
The LTC1473L uses an adaptive inrush current limiting
scheme to reduce current flowing in and out of the battery
and the following system’s input capacitor during switch-
over transitions. The voltage across a single small valued
resistor, R
neous current flowing through either of the two switch
pairs, SW A1/B1 and SW A2/B2, during the transitions.
SENSE
GG
+
GG
output capacitor C2.
pin is diode ORed through two external
, is measured to ascertain the instanta-
) Power Supply
U
GG
is regulated at 8.5V above the
+
as shown in Figure 1. C1
+
, up to 20V
Figure 2 shows a block diagram of a switch driver pair, SW
A1/B1. A bidirectional current sensing and limiting circuit
determines when the voltage drop across R
priate switch is limited during the transition period until
the inrush current subsides.
This scheme allows capacitors and MOSFET switches of
differing sizes and current ratings to be used in the same
system without circuit modifications.
200mV. The gate-to-source voltage, V
BAT1
LTC1473L
V
GG
LTC1473L
DRIVERS
TO GATE
SW A1
Figure 2. SW A1/B1 Inrush Current Limiting
GA1
6V
DRIVERS
SW A/B
GATE
Figure 1. V
SAB1
REGULATOR
SWITCHING
6V
SW B1
V
(8.5V + V
GG
GB1
GG
+
INRUSH CURRENT
Switching Regulator
)
BIDIRECTIONAL
V
SENSING AND
THRESHOLD
SENSE +
LIMITING
R
200mV
SENSE
GND
V
SW
V
GG
+
DCIN
LTC1473L
V
SENSE –
L1
1mH
GS
BAT1
, of the appro-
1473 F02
SENSE
+
C2
1 F
25V
1473 F01
C
OUT
reaches
OUTPUT
LOAD
C1
1 F
25V
7