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LT3015

3015f

BLOCK DIAGRAM

–1.20V

1.21V

VREF

ADJ

SHDN

I LIMIT FOLDBACK

OUT

NPN DRIVER

BIAS CIRCUITRY

ADJ PIN BIAS CURRENT

COMPENSATION

QPOWER

3015 BD

VTH

RSNS

–

ERROR AMP

–

I LIMIT AMP

GND

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

APPLICATIONS INFORMATION

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 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

GND

LT3015

ADJ

OUT

SHDN

VOUT

CIN

VIN

COUT

3015 F01

Figure 1. Adjustable Operation

VOUT = –1.22V 1+

⎛

⎝⎜

⎞

⎠⎟ +

IADJ

() R2

()

VADJ = –1.22V ANDIADJ = 30nA AT 25°C

OUTPUT RANGE

= –1.22 TO – 29.5V

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