LT3015IQ-12 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LT3015IQ-12 Datasheet PDF : 26 Pages
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BLOCK DIAGRAM
1.21V
_
+
SHDN
–
–1.20V
+
*SEE TABLE 1 FOR
NOMINAL VALUES
OF R1 AND R2
SENSE
R2*
R1*
ADJ
VREF
–
ERROR AMP
+
BIAS CIRCUITRY
+
I LIMIT AMP
–
ADJ PIN BIAS CURRENT
GND
COMPENSATION
IN
LT3015 Series
OUT
NPN DRIVER
QPOWER
RSNS
VTH
+
I LIMIT FOLDBACK
3015 BD
APPLICATIONS INFORMATION
The LT3015 series are 1.5A negative low dropout linear
regulators featuring precision current limit and precision
bi-directional shutdown. The device supplies up to 1.5A
of output load current at a typical dropout voltage of
310mV. Moreover, the low 1.1mA operating quiescent
current drops to less than 1µA in shutdown. In addition
to low quiescent current, the LT3015 incorporates several
protection features that make it ideal for battery powered
applications. In dual supply applications where the regu-
lator’s load is returned to a positive supply, OUT can be
pulled above GND by 30V and still allow the LT3015 to
start up and operate.
Adjustable Operation
The LT3015 adjustable version has an output voltage
range of –1.22V to –29.3V. Output voltage is set by the
ratio of two external resistors as shown in Figure 2. The
device regulates the output to maintain the ADJ pin voltage
to –1.22V referred to ground. The current in R1 equals
–1.22V/R1 and the current in R2 equals the current in R1
plus the ADJ pin bias current. The ADJ pin bias current,
30nA at 25°C, flows into the ADJ pin. Calculate the output
voltage using the formula shown in Figure 1. The value
of R1 should be less than 50k to minimize errors in the
output voltage created by the ADJ pin bias current. Note
that in shutdown, the output is off and the divider current
GND
CIN
LT3015
R1
VIN
SHDN
ADJ
R2
IN
OUT
3015 F02
( ) VOUT
=
–1.22V
1+
R2
R1
+
IADJ
(R2)
VADJ = –1.22V AND IADJ = 30nA AT 25°C
OUTPUT RANGE = –1.22 TO – 29.5V
Figure 2. Adjustable Operation
COUT
VOUT
is zero. Curves of ADJ Pin Voltage vs Temperature, ADJ
Pin Bias Current vs Temperature and ADJ Pin Bias Cur-
rent vs Input Voltage appear in the Typical Performance
Characteristics section.
The adjustable device is tested and specified with the
ADJ pin tied to the OUT pin for a –1.22V output voltage.
Specifications for output voltages greater than –1.22V are
proportional to the ratio of the desired VOUT to –1.22V
(VOUT/–1.22V). For example, load regulation for an out-
put current change of –1mA to –1.5A is typically 2mV at
VOUT = –1.22V. At VOUT = –5V, load regulation equals:
(–5V/–1.22V) • (2mV) = 8.2mV
3015fb
15
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