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TCL1585

7A / 5A / 4.6A / 3A, FAST RESPONSE, LOW DROPOUT POSITIVE LINEAR VOLTAGE REGULATORS

TelCom Semiconductor, Inc 

7A / 5A / 4.6A / 3A, FAST RESPONSE,

LOW DROPOUT POSITIVE LINEAR

VOLTAGE REGULATORS

PRELIMINARY INFORMATION

TCL1584

TCL1585

TCL1587

Output Voltage

The output voltage for the fixed output versions of the

TCL158x is set internally and cannot be adjusted. For the

adjustable output versions, the output voltage is set by two

external resistors: R1 and R2 (see Figure 3). A 1.25V

reference voltage is maintained between the OUTPUT pin

and the ADJ pin. NOTE: the ADJ pin typically will source

55µA. R1 should be chosen to conduct at least the specified

minimum load current of 10mA (i.e. at most 125Ω). Now R2

will determine the total output voltage according to the

equation below:

VOUT = VREF(1+ R2/R1) + R2(IADJ)

The contribution due to the IADJ term is relatively small

as IADJ is only 55µA compared to 10mA for the total current

in the adjust circuit.

RP

PARASITIC

LINE RESISTANCE

VIN

IN TCL1584-3.3 OUT

GND

RL

Figure 5. Connection for Best Load Regulation

In both cases, because the effect of parasitic trace

resistance (RP) cannot be completely eliminated, it is impor-

tant to keep the positive output lead as short as possible.

Otherwise, at high output currents, the load regulation will

degrade appreciably. Example:

VIN

C1 +

10µF

IN TCL1584 OUT

ADJ

IADJ

55µA

VREF

R1

( ) VOUT = VREF 1+ R2 + IADJ (R2)

R2

R1

VOUT

C2

22µF

Figure 4. Adjustable Voltage Regulator

RP = 5mΩ

IOUT = 3A

VDROP = (0.005) x (3) = 15mV

RP

PARASITIC

LINE RESISTANCE

VIN

IN TCL1584 OUT

ADJ

Load Regulation

R1*

RL

Because the TCL158x family are three terminal de-

vices, it is not possible to perform true Kelvin load voltage

R2*

sensing. Therefore load regulation is limited somewhat by

parasitic trace resistance. The load regulation specifications

are measured directly at the TCL158x package. To minimize

degradation in load regulation performance the following

guidelines should be used.

*CONNECT R1 TO CASE

CONNECT R2 TO LOAD

For fixed voltage devices, the GND pin should be

connected directly to the negative side of the load instead of

Figure 6. Connection for Best Load Regulation

to a common ground bus. This provides Kelvin sensing at

the negative side while the positive side is still limited by RP

(See Figure 5).

Thermal Considerations

For adjustable output devices, the bottom of R2 con-

The TCL158x family includes built-in thermal overload

nects to the negative side of the load. For the positive side, protection. However, maximum operating junction tempera-

best regulation is obtained when the top of R1 is connected ture must not be exceeded for any condition. Since these

directly to the TCL158x and not to the load (See Figure 6). devices are capable of dissipating up to 25W or more under

If R1 connects to the load the effective resistance between some conditions, careful thermal design is required for

the output and the load is:

reliable, continuous operation. In most cases, external heat

sinking will be required.

RP x (1 + R2/R1)

TCL1584/1585/1587-04 6/6/97

7

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