LT1528CQ Linear Technology, LT1528CQ Datasheet - Page 7

• Manufacturer Part Number: LT1528CQ
• Description: IC LDO REG 3.3V/ADJ 3A DDPAK-5
• Manufacturer: Linear Technology

Specifications of LT1528CQ

• Regulator Topology: Positive Fixed and Adjustable
• Voltage - Output: 3.3V, 3.3 ~ 14.15 V
• Voltage - Input: 3.9 ~ 15 V
• Voltage - Dropout (typical): 0.57V @ 3A
• Number Of Regulators: 1
• Current - Output: 3A
• Current - Limit (min): 3.2A
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TO-263-5, D²Pak (5 leads + Tab), TO-263BA
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

PIN FUNCTIONS
SHDN (Pin 4): This pin is used to put the device into
shutdown. In shutdown the output of the device is turned
off. This pin is active low. The device will be shut down if
the SHDN pin is actively pulled low. The SHDN pin current
with the pin pulled to ground will be 60μA. The SHDN pin
is internally clamped to 7V and – 0.6V (one V
lows the SHDN pin to be driven directly by 5V logic or by
open collector logic with a pull-up resistor. The pull-up
resistor is only required to supply the leakage current of
the open collector gate, normally several microamperes.
Pull-up current must be limited to a maximum of 5mA.
A curve of SHDN pin input current as a function of volt-
age appears in the Typical Performance Characteristics
section. If the SHDN pin is not used it can be left open
circuit. The device will be active output on if the SHDN
pin is not connected.
V
input pin. The input pin should be bypassed to ground if
APPLICATIONS INFORMATION
The LT1528 is a 3A low dropout regulator optimized for
microprocessor applications. Dropout voltage is only 0.6V
at 3A output current. With the SENSE pin shorted to the
OUTPUT pin, the output voltage is set to 3.3V. The device
operates with a quiescent current of 400μA. In shutdown,
the quiescent current drops to only 125μA. The LT1528
incorporates several protection features, including protec-
tion against reverse input voltages. If the output is held
at the rated output voltage when the input is pulled to
ground, the LT1528 acts like it has a diode in series with
its output and prevents reverse current fl ow.
Adjustable Operation
The LT1528 can be used as an adjustable regulator with
an output voltage range of 3.3V to 14V. The output voltage
is set by the ratio of two external resistors as shown in
Figure 2. The device servos the output voltage to maintain
the voltage at the SENSE pin at 3.3V. The current in R1
is then equal to 3.3V/R1. The current in R2 is equal to
the sum of the current in R1 and the SENSE pin current.
The SENSE pin current, 130μA at 25°C, fl ows through R2
IN
(Pin 5): Power is supplied to the device through the
BE
). This al-
the device is more than six inches away from the main
input fi lter capacitor. The LT1528 is designed to withstand
reverse voltages on the input pin with respect to ground
and the OUTPUT pin. In the case of reversed input, the
LT1528 will act as if there is a diode in series with its input.
There will be no reverse current fl ow into the LT1528 and
no reverse voltage will appear at the load. The device will
protect both itself and the load.
into the SENSE pin. The output voltage can be calculated
using the formula in Figure 2. The value of R1 should be
less than 330Ω to minimize errors in the output voltage
caused by the SENSE pin current. Note that in shutdown
the output is turned off and the divider current will be
zero. Curves of SENSE Pin Voltage vs Temperature and
SENSE Pin Current vs Temperature appear in the Typical
Performance Characteristics section.
V
IN
V
+
IN
Figure 1. Kelvin Sense Connection
Figure 2. Adjustable Operation
V
V
I
OUTPUT RANGE = 3.3V TO 14V
SENSE
5
4
OUT
SENSE
5
4
IN
SHDN
= 3.3V 1 +
IN
SHDN
= 130μA AT 25°C
= 3.3V
LT1528
)
GND
LT1528
GND
R2
R1
3
3
SENSE
)
+ (I
SENSE
OUT
SENSE
OUT
1
2
)(R2)
1
2
R
R
P
R2
R1
P
+
LT1528
+
1528 F01
1528 F02
V
LOAD
OUT
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