SMM105
Preliminary Information
APPLICATIONS INFORMATION (CONTINUED)
+12VIN (+10V to +15V)
RTRIM(R3) is calculated as follows:
VTRIMlow=0.3V, Regulator VREF=0.8V
The current through R3 is ITRIM=(0.8-0.3)/RTRIM
(ITRIM)(R4) > 15% of VOUT
C4
C7
0.1uF
0.01uF
C8
RTRIMmax should be < the calculated value
0.1uF
For Example:
If Vout=3.3V, R4=63.4K, 15% of Vout=0.5V
ITRIM=8uA, RTRIM=62.5K
R6 10K
R7 10K
R8 10K
Therefore Rtrim standard 1% value down from 62.
U1
C1 1uF
START
READY
FAULT#
3
5
18
20
14
19
12
RTRIM
R3
START
READY
FAULT#
TRIM_CAP
TRIM
VOUT
11
VM
COMP1
U2 Switching Regulator
R4
RSET1
SMM105 COMP2
R2 10K
R1 10K
1
28
6
SCL
SDA
A0
+Vin
+Vout
10
8
FILT_CAP
4
A1
WP#
PGOOD
2
A2
VADJ (VREF)
C5
0.02uF
R5
D1
20k
DIODE
START
J1
1
3
5
7
9
2
Gnd
SCL
SDA
MR
4
Gnd3
Rsrv5
6
8
+10V Rsrv8
+5V Rsrv10
10
The SMM105 START pin must be inactive during power-up so
that the TRIM pin is high impedence. Once power is nominal,
the START pin can be active to start margin and ADOC
functions
SMX3200 I2C Programming
Connector 10 pin Header
R1 and R2 need only be
placed once on the I2C bus
Figure 7 – SMM105 Applications schematic for an adjustable switching regulator (Full regulator circuit not
shown).
Summit Microelectronics, Inc
2068 1.8 09/20/05
11
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
