LT3015EDD Datasheet, PDF (11/20 Pages) Linear Technology – 1.5A, Low Noise, Negative Linear Regulator with Precision Current Limit

BLOCK DIAGRAM
1.21V
_
+
SHDN
–
–1.20V
+
GND
LT3015
ADJ
V_REF
–
ERROR AMP
+
BIAS CIRCUITRY
+
I LIMIT AMP
–
ADJ PIN BIAS CURRENT
COMPENSATION
IN
OUT
NPN DRIVER
QPOWER
R_SNS
V_TH
+
I LIMIT FOLDBACK
3015 BD
APPLICATIONS INFORMATION
The LT3015 regulator is a 1.5A negative low dropout linear
regulator 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 regulator has an output voltage range of –1.22V
to –29.5V. Output voltage is set by the ratio of two external
resistors as shown in Figure 1. 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 is zero. Curves of
GND
C_IN
LT3015
R1
V_IN
SHDN
ADJ
R2
IN
OUT
3015 F01
( ) V_OUT
=
–1.22V
⎛⎝⎜₁₊
R2⎞
R1^⎠⎟
+
I_ADJ
(R2)
V_ADJ = –1.22V AND I_ADJ = 30nA AT 25°C
OUTPUT RANGE = –1.22 TO – 29.5V
Figure 1. Adjustable Operation
C_OUT
V_OUT
ADJ Pin Voltage vs Temperature, ADJ Pin Bias Current vs
Temperature and ADJ Pin Bias Current 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 V_OUT to –1.22V
(V_OUT/–1.22V). For example, load regulation for an out-
put current change of –1mA to –1.5A is typically 2mV at
V_OUT = –1.22V. At V_OUT = –5V, load regulation equals:
(–5V/–1.22V) • (2mV) = 8.2mV
3015f
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