LTC3576-1_15 Datasheet, PDF (21/48 Pages) Linear Technology – Switching Power Manager with USB On-the-Go Triple Step-Down DC/DCs

OPERATION
LTC3576/LTC3576-1
TO AUTOMOTIVE,
FIREWIRE, ETC.
V_IN
HIGH VOLTAGE _SW
STEP-DOWN
V_C
SWITCHING
REGULATOR
FB
OVSENS
6
OVGATE
5
OVERVOLTAGE PROTECTION
26
V_C
6V
s2
+–
27
WALL
V_OUT
–
3.6V
BAT + 0.3V 4.3V
+
Bat-Track HV CONTROL
ACPR
28
TO USB
CABLE
35 ^VBUS
34 ^VBUS
I_SWITCH/N
PWM AND
GATE DRIVE
V_BUS
VOLTAGE
CONTROLLER
–
+
5V
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
IDEAL
DIODE
+
OmV
–
15mV ^+–
SW
36
V_OUT
33
IDGATE
31
3.5V TO
(BAT + 0.3V)
TO SYSTEM LOAD
OPTIONAL EXTERNAL
IDEAL DIODE PMOS
CLPROG –
1
+
1.15V
0.3V
+–
3.6V
BAT
32
AVERAGE V_BUS OUTPUT
CURRENT LIMIT
CONTROLLER
V_OUT VOLTAGE
CONTROLLER
3576 F03
BATTERY POWER
HV INPUT
Figure 3. PowerPath Block Diagram—USB On-the-Go
+ _{SINGLE CELL}
Li-Ion
high voltage switching regulator. As a step-up converter,
the bidirectional switching regulator produces 5V on
V_BUS and is capable of delivering at least 500mA. USB
on-the-go can be enabled by either the external control
pin, ENOTG, or via I²C. Figure 3 shows the power flow
in step-up mode.
An undervoltage lockout circuit monitors V_OUT and pre-
vents step-up conversion until V_OUT rises above 2.8V. To
prevent backdriving of V_BUS when input power is available,
the V_BUS undervoltage lockout circuit prevents step-up
conversion if V_BUS is greater than 4.3V at the time step-up
mode is enabled. The switching regulator is also designed
to allow true output disconnect by eliminating body diode
conduction of the internal PMOS switch. This allows V_BUS
to go to zero volts during a short-circuit condition or while
shut down, drawing zero current from V_OUT.
The voltage regulation loop is compensated by the capaci-
tance on V_BUS. A 4.7μF MLCC is required for loop stability.
Additional capacitance beyond this value will improve
transient response. The V_BUS voltage has approximately
3% load regulation up to an output current of 500mA. At
light loads, the switching regulator goes into Burst Mode
operation. The regulator will deliver power to V_BUS until it
reaches 5.1V after which the NMOS and PMOS switches
shut off. The regulator delivers power again to V_BUS once
it falls below 5.1V.
The switching regulator features both peak inductor and
average output current limit. The peak current mode
architecture limits peak inductor current on a cycle-by-
cycle basis. The peak current limit is equal to V_BUS/2Ω to
a maximum of 1.8A so that in the event of a sudden short
circuit, the current limit will fold back to a lower value.
In step-up mode, the voltage on CLPROG represents the
average output current of the switching regulator when
a programming resistor and an averaging capacitor are
connected from CLPROG to GND. With a 3.01k resistor
on CLPROG, the bidirectional switching regulator has an
output current limit of 680mA. As the output current ap-
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