LTC1438/LTC1439
PIN FUNCTIONS
12V operation. When used as a comparator, this is the
noninverting input of a comparator whose inverting input
is tied to the internal 1.19V reference. See Auxiliary Regu-
lator Application section.
AUXON: Pulling this pin high turns on the auxiliary regu-
lator/comparator. The threshold is 1.19V. This is a conve-
nient linear power supply logic-controlled on/off input.
AUXDR: Open Drain Output of the Auxiliary Regulator/
Comparator. The base of an external PNP device is con-
nected to this pin when used as a linear regulator. An
external pull-up resistor is required for use as a compara-
tor. A voltage > 9.5V on AUXDR causes the internal 12V
resistive divider to be connected in series with the AUXFB pin.
W
FUNCTIONAL DIAGRA
PLLIN**
fIN
50k
CLP
COSC
RLP PLL LPF**
COSC
POR2
LBI
BATTERY
SENSE
LBO
PHASE
DETECTOR
2.4V
OSCILLATOR
POWER-ON
RESET
VFB2
1.11V
VSEC
AUXON**
VLDO
+
AUXDR**
AUXFB**
+
9V –
90.8k
10k
+
SFB1*
–
VIN 1µA
VIN
4.8V +
–
EXTVCC
SFB
1.19V
VREF
REF
5V LDO
REGULATOR
INTVCC
+
SGND
INTERNAL
SUPPLY
DUPLICATE FOR SECOND CONTROLLER CHANNEL
VIN
BOOST
INTVCC
DB
DROPOUT
DETECTOR
SQ
SFB
RQ
0.6V +
–
+
SHUTDOWN
SWITCH
LOGIC
I1
INTVCC
TGL
TGS**
SW
BG
PGND
–
30k
8k
180k
VFB
EA
gm = 1m
I2
4k
320k
61k
119k
INTVCC
SENSE –
SENSE +
VOSENSE*
VPROG*
CB
•
+•
CIN
COUT RSENSE
VOUT
CSEC
0V
3µA
6V
1.28V
1.19V
SHUTDOWN
RUN
SOFT START
DFB†
ITH
CC
RC
RUN/SS
CSS
*IN SOME VERSIONS, NOT AVAILABLE ON BOTH CHANNELS **NOT AVAILABLE ON LTC1438
†FOLDBACK CURRENT LIMITING OPTION
BOLD LINES INDICATE HIGH CURRENT PATHS
1438 FD
9