LTC1553
PIN FUNCTIONS
VID0, VID1, VID2, VID3, VID4 (Pins 18, 17, 16, 15, 14):
Digital Voltage Select. TTL inputs used to set the regulated
output voltage required by the processor (Table 3). There
is an internal 20kΩ pull-up at each pin. When all five VID
n
pins are high or floating, the chip will shut down.
OUTEN (Pin 19):
Output Enable. TTL input which enables
the output voltage. The external MOSFET temperature can
be monitored with an external thermistor as shown in
Figure 13. When the OUTEN input voltage drops below 2V,
OT trips. As OUTEN drops below 1.7V, the drivers are
internally disabled to prevent the MOSFETs from heating
further. If OUTEN is less than 1.2V for longer than 30µs,
the LTC1553 will enter shutdown mode. The internal
oscillator can be synchronized to a faster external clock by
applying the external clocking signal to the OUTEN pin.
G1 (Pin 20):
Gate Drive for the Upper N-Channel MOSFET,
Q1. This output will swing from PV
CC
to GND. It will always
be low when G2 is high or the output is disabled.
BLOCK DIAGRAM
115% V
REF
+
FC
12 FAULT
11 OT
DELAY
LOGIC
DISDR
SYSTEM
POWER
DOWN
13 PWRGD
–
OUTEN 19
COMP 10
I
SS
SS 9
Q
SS
ERR
+
–
V
REF
MHCL
HCL MONO
+
–
W
U
U
U
2 PV
CC
R
PWM
S
20 G1
1 G2
BG
MIN
MAX
–
+
–
+
FB
6 SENSE
18 VID0
17 VID1
16 VID2
V
REF
– 5%
V
REF
+ 5%
–
CC
8 I
FB
15 VID3
14 VID4
DAC
+
7 I
MAX
I
MAX
V
REF
+
LVC
0.5V
REF
/
0.7V
REF
–
1553 BD
7
LINER [ LINEAR TECHNOLOGY ]
