SC2602L Semtech Corporation, SC2602L Datasheet - Page 5

• Manufacturer Part Number: SC2602L
• Description: Synchronous Voltage Mode Controller
• Manufacturer: Semtech Corporation

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Synchronous Buck Converter
The output rail is regulated by a synchronous, voltage-
mode pulse width modulated (PWM) controller. This
section has all the features required to build a high effi-
ciency synchronous buck converter, including “Power
Good” flag, shut-down, and cycle-by-cycle current limit.
The output voltage of the synchronous converter is set
and controlled by the output of the error amplifier. The
external resistive divider reference voltage is derived from
an internal trimmed-bandgap voltage reference (See Fig.
1). The inverting input of the error amplifier receives its
voltage from the SENSE pin.
The internal oscillator uses an on-chip capacitor and
trimmed precision current sources to set the oscillation
frequency to 200kHz. The triangular output of the oscil-
lator sets the reference voltage at the inverting input of
the comparator. The non-inverting input of the compara-
tor receives it’s input voltage from the error amplifier.
When the oscillator output voltage drops below the er-
ror amplifier output voltage, the comparator output goes
high. This pulls DL low, turning off the low-side FET, and
DH is pulled high, turning on the high-side FET (once
the cross-current control allows it). When the oscillator
voltage rises back above the error amplifier output volt-
age, the comparator output goes low. This pulls DH low,
turning off the high-side FET, and DL is pulled high, turn-
ing on the low-side FET (once the cross-current control
allows it).
Theory of Operation
 2005 Semtech Corp.
POWER MANAGEMENT
Block Diagram
SS/SHDN
PWRGD
SENSE
COMP
OVP
GND
VCC
VCC
VCC
10uA
1.5uA
Vbg
+10%
-10%
+20%
Error Amp
0.8V
0.6V
0.8V
Vbg
Under
Voltage
S
S
R
R
QB
QB
5
As SENSE increases, the output voltage of the error
amplifier decreases. This causes a reduction in the on-
time of the high-side MOSFET connected to DH, hence
lowering the output voltage.
Under Voltage Lockout
The under voltage lockout circuit of the SC2602L as-
sures that the high-side MOSFET driver outputs remain
in the off state whenever the supply voltage drops below
set parameters. Lockout occurs if V
Normal operation resumes once V
Over-Voltage Protection
The over-voltage protection pin (OVP) is high only when
the voltage at SENSE is 20% higher than the target value
programmed by the external resistor divider. The OVP
pin is internally connected to a PNP’s collector.
Power Good
The power good function is to confirm that the regulator
outputs are within +/-10% of the programmed level.
PWRGD remains high as long as this condition is met.
PWRGD is connected to an internal open collector NPN
transistor.
Oscillator
Fault
PWM
One Shot
Over Current
Cross
Current
Control
DRVL
DRVL
DRVH
DRVH
200uA
CC
CC
rises above 4.2V.
SC2602L
falls below 4.1V.
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PHASE
BSTL
OCSET
BSTH
DH
DL
PGND