SC1112 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC1112' PDF : 23 Pages View PDF
SC1112
POWER MANAGEMENT
Applications Infomation (Cont.)
+3.3V
+5V STBY
SC1112
5VSTBY
GND
ADJGATE AGPGATE
ADJSEN
AGPSEN
CAP-
VTTGATE
CAP+
VTTSEN
FC
AGPSEL
DELAY
VTTSEL
PWRGD
VTTIN
C3
0.1u
C1
10u
Q3
C2 C18
Q1
330u
C19
C8 C9
330u 330u 0.1u
C14
330u
AGP
C16 C17
330u 0.1u
VTT
R1
VTT SELECT Signal
AGP SELECT Signal
R2
Figure 1: Adjusting The Output Voltage of VTT or AGP
Adjustable Output Voltage Option
The adjustable output voltage option does not have an
internal resistor divider. The adjust pin connects directly to
the inverting input of the error amplifier, and the
output voltage is set using external resistors (please
refer to Figure 2). In this case, the adjust pin sources a
nominal 0.5µA, so the resistor values should be selected
to allow 50µA to flow through the divider. Again, a target
value for RB (maximum) can be
calculated:
RB
≤
1.200 V
50µA
Ω
The output voltage can be calculated as follows:
VOUT
=
1.200
•
1 +
RA
RB
−
0.5µA
• RA
The maximum output voltage that can be obtained from
the adjustable option is determined by the input supply
voltage and the R and gate threshold voltage of the
DS(ON)
external MOSFET. Assuming that the MOSFET gate
threshold voltage is sufficiently low for the output
voltage chosen and a worst-case drive voltage of 9V, VOUT(MAX)
is given by:
VOUT(MAX) = VTTIN(MIN) − IOUT(MAX) • RDS(ON)(MAX)
C6
330u
C13
C12
0.1u
330u
VTT
1K
R1
POWER GOOD
Q2
0.1u C11
RA
1u C10
RB
22n C5
SC11
5VSTBY
ADJGATE
ADJSEN
CAP-
CAP+
FC
DELAY
PWRGD
Figure 2
2006 Semtech Corp.
17
www.semtech.com
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