Datasheet

LTC2970/LTC2970-1
34
29701fc
Q1
TP0610K
OUT
FB
R10
R20
R
SENSE
0.1μF
0.1μF
I
2
C BUS
LOAD
DC/DC
CONVERTER
V
IN
V
EE
GND
R20
R10
29701 F05
1/2 LTC2970
ALERT
SCL
SDA
REF
12V
IN
GND ASEL0 ASEL1
V
DD
V
IN0_BP
V
IN0_BM
V
IN0_AP
I
OUT0
V
IN0_AM
8V TO 15V
0.1μF
V
OUT
= V
DD
–
(
1 +
R30
R40
)
V
IN0_AP
– V
IN0_AM
•
(
)
Figure 4 shows the DC/DC converter output voltages for
this design example tracking-up and tracking-down.
Temperature Sensor Conversion
The LTC2970's internal temperature sensor output is
proportional to absolute temperature (PTAT). In order to
convert the ADC reading to degress Celsius, apply the
following formula:
result C
ADC temp sensor reading
()
__ _
.°= −
4
273 15
(21)
Negative Power Supply Application Circuit
Figure 5 shows the LTC2970 controlling a negative power
supply. The R30/R40 resistor divider translates the point
of load voltage to the LTC2970’s V
IN0_A
inputs while the
V
IN0_B
inputs monitor the converter’s input current I • R
drop across resistor R
SENSE
. Since the V
DD
pin voltage
is monitored by the LTC2970, its tolerance can be ac-
counted for when calculating the point of load voltage.
Transistor Q1 allows the I
OUT0
pin to force current into
the converter’s feedback node without forward biasing
the LTC2970’s I
OUT0
body diode. Note that I
OUT0
’s output
current defaults to 128μA after the LTC2970 comes out
of power-on reset.
15-Bit Programmable Power Supply Application
Circuit
Figure 6 illustrates how both servo channels of the LTC2970
can be confi gured to adjust a single DC/DC converter over
a 15-bit dynamic range. R30 and R31 are sized to force
1 bit of overlap between the coarse (channel 0) and fi ne
(channel 1) servo loops. One coarse servo iteration should
be performed fi rst on channel 0 with IDAC1 programmed
to mid-scale, and then channel 1 can be programmed to
servo to the desired voltage.
Programmable Reference Application Circuit
Figure 7 shows a LTC2970 confi gured as a program-
mable reference that can span a 0V to 3.5V range with
a resolution of 100μV and an absolute accuracy of less
than ±0.5%. The two IDAC’s are paralleled by terminating
IDAC1’s output resistor in the V
OUT0
output and taking the
output of the composite DAC from V
OUT1
. IDAC0 should
servo once with IDAC1 set to mid-scale, and then IDAC1
can servo once, continuously, or trigger on drift to the
desired target voltage.
Figure 4. Tracking Design Example DC/DC
Converter Output Waveforms
APPLICATIO S I FOR ATIO
WUU
U
Figure 5. Negative Power Supply Application Circuit
Figure 6. Programmable Power Supply Application Circuit
0
0.3
0.9
1.2
1.5
2.7
29701 F04
0.6
5ms/DIV
VOLTS
1.8
2.1
2.4
V
DC1
V
DC0
OUT
FB
R40R10
R20
R30
0.1μF
0.1μF
I
2
C BUS
LOAD
DC/DC
CONVERTER
SGND
29701 F06
R31
R31 ≥ R30 • 128
R41 = R40
RUN/SS
IN
V
IN
LTC2970
ALERT
SCL
SDA
GPIO_0
REF
12V
IN
GND
GND
ASEL0 ASEL1
V
DD
GPIO_CFG
V
OUT1
V
IN1_AP
V
IN0_AP
V
IN1_AM
V
OUT0
I
OUT0
R41
I
OUT1
V
IN0_AM
C
LOAD
+
8V TO 15V
0.1μF