sc1175 Semtech Corporation, sc1175 Datasheet - Page 6

• Manufacturer Part Number: sc1175
• Description: Sc1175 Low-power Dual Synchronous Dc/dc Controller With Current-sharing Circuitry
• Manufacturer: Semtech Corporation

POWER MANAGEMENT
NOTES
(1) Block 1 (top) is the Master and Block 2 (bottom) is the Slave in current sharing configuration.
(2) For independant operation there is no Master or Slave.
Main Loop(s)
The SC1175 is a dual, voltage mode synchronous Buck
controller, the two separate channels are identical and
share only IC supply pins (Vcc and GND), output driver
ground (PGND) and pre-driver supply voltage (BSTC). They
also share a common oscillator generating a sawtooth
waveform for channel 1 and an inverted sawtooth for
channel 2. Each channel has its own current limit com-
parator. Channel 1 has the positive input of the error
amplifier internally connected to Vref. Channel 2 has
both inputs of the error amplifier uncommitted and avail-
able externally. This allows the SC1175 to operate in two
distinct modes.
Block Diagram
Applications Information - Theory of Operation
2004 Semtech Corp.
a) Two independent channels with either common or
different input voltages and different output voltages.
The two channels each have their own voltage feed-
6
back path from their own output. In this mode, the
positive input of error amplifier 2 is connected exter-
nally to Vref. If the application uses a common input
voltage, the sawtooth phase shift between the chan-
nels provides some measure of input ripple current
cancellation.
b)
with common output voltage and either common in-
put voltage or different input voltages. In this mode,
channel 1 operates as a voltage mode Buck control-
ler, as before, but error amp 2 monitors and amplifies
the difference in voltage across the output current
sense resistors of channel 1 and channel 2 (Master
and Slave) and adjusts the Slave duty cycle to match
output currents. Because of finite gain and offsets in
the loop, the resistor ratio for perfect current match-
ing is not 1:1. The Master and Slave channels still have
Two channels operating in current sharing mode
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SC1175