LTC2970-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2970-1' PDF : 36 Pages View PDF
LTC2970/LTC2970-1
APPLICATIO S I FOR ATIO
2.7
2.4
VDC1
2.1
1.8
VDC0
1.5
1.2
0.9
0.6
0.3
0
5ms/DIV
29701 F04
Figure 4. Tracking Design Example DC/DC
Converter Output Waveforms
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 − 273.15
4
(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 VIN0_A inputs while the
VIN0_B inputs monitor the converter’s input current I • R
8V TO 15V
0.1μF
R20
R10
VDD 12VIN
VIN0_AP
VIN0_AM
1/2 LTC2970
0.1μF
RSENSE
VIN0_BP
ALERT
SCL
I2C BUS
GND
OUT
DC/DC
CONVERTER
FB
VIN
VIN0_BM
SDA
Q1
TP0610K
IOUT0
REF
GND ASEL0 ASEL1
0.1μF
R20
LOAD
R10
VEE
29701 F05
( ) ( ) VOUT = VDD –
1 + R30
R40
•
VIN0_AP – VIN0_AM
Figure 5. Negative Power Supply Application Circuit
34
drop across resistor RSENSE. Since the VDD 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 IOUT0 pin to force current into
the converter’s feedback node without forward biasing
the LTC2970’s IOUT0 body diode. Note that IOUT0’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 configured 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 fine
(channel 1) servo loops. One coarse servo iteration should
be performed first 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 configured 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 VOUT0 output and taking the
output of the composite DAC from VOUT1. 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.
8V TO 15V
VIN IN OUT
+
CLOAD
DC/DC
CONVERTER
R31
R30
RUN/SS FB
GND SGND
R20
LOAD
R10
R31 ≥ R30 • 128
R41 = R40
12VIN
VDD
LTC2970
GPIO_CFG
VOUT1
VOUT0
VIN0_AP
VIN1_AP
ALERT
SCL
SDA
IOUT1
R41
IOUT0
GPIO_0
R40
VIN0_AM
REF
VIN1_AM
GND ASEL0 ASEL1
0.1μF
0.1μF
I2C BUS
0.1μF
29701 F06
Figure 6. Programmable Power Supply Application Circuit
29701fc
Share Link: 
