SC631
10
General Description
The SC631 is a 4.4V output charge pump regulator
designed to support up to 325mA (T
A
≤ 55°C, 2.92V ≤ V
IN
≤
5.5V) and 250mA (T
A
≤ 85°C, 2.90V ≤ V
IN
≤ 5.5V) of continu-
ous current. SC631 applications include power for LEDs
and audio ampli ers in portable handheld equipment.
SC631 may be used in conjunction with regulated current
sink devices such as the SC620 Octal LED Driver or with
ballast resistors.
The SC631 has three operating modes — 1x, 1.5x, and 2x.
The 1x mode is a linear series regulation mode with a low
open-loop output resistance of only 250m
Ω. The 1x mode
functions as a low-noise linear regulator. The 1.5x and 2x
modes are a low noise, constant frequency, constant duty
cycle switch mode, using two bucket capacitors. One
bucket supports the full output current while the other
bucket charges from the input. The two buckets exchange
roles in the next phase, supplying continuous output
current in both phases and reducing the need for a large
output decoupling capacitor. The constant frequency,
constant duty cycle operation also produces predictable
constant frequency harmonics.
Mode Transition Hysteresis
Hysteresis is provided to prevent chatter between charge
pump modes for input steps of up to 120mV. For optimum
transient performance, it is recommended for the supply
decoupling capacitance be large enough to prevent steps
greater than 120mV. Normally C
IN
= 22uF is su cient to
minimize supply transients during the charge pump mode
transitions.
Thermal Resistance
The SC631 package is thermally e cient when the circuit
board layout connects the thermal pad through multiple
vias to the ground plane. The thermal resistance rating is
dependent upon the connection between the thermal
pad and the ground plane. A layout that is done correctly
should keep the junction temperature below the over-
temperature limit while operating the SC631 within the
speci ed electrical conditions. A poor layout may allow
the junction temperature to reach the over temperature
limit, so it is important to maintain adequate ground
plane around the device to maximize heat transfer to the
PCB.
Temperature Derating
The V
IN
supply range and ambient temperature range of
the application should be compared with the following
derating curve to determine the maximum safe continu-
ous load current. The DC operating points beneath each
curve are in the safe operating temperature range of the
MLP package.
150
200
250
300
350
400
450
35 45 55
65 75
85
Ambient Temp (°C)
I
OUT
(mA)
Derating for V
IN
< 4.2V
Derating for V
IN
< 5.5V
Maximum Continuous Output
Protection Circuitry
The SC631 also provides protection circuitry that pre-
vents the device from operating in an unspeci ed state.
These functions include:
Over-Current Protection (OCP)
Short-Circuit Current Protection (SCCP)
Over-Temperature Protection (OTP)
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•
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Applications Information
