LMZ10501SH datasheet(15/25 Pages) TI

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10 PF

PGND

SGND

10 PF

CVC

VCON

VIN

VREF

VOUT

CIN

COUT

LMZ10501

www.ti.com

SNVS677D – MAY 2011 – REVISED MARCH 2013

THERMAL OVERLOAD PROTECTION

The junction temperature of the LMZ10501 should not be allowed to exceed its maximum operating rating of

125°C. Thermal protection is implemented by an internal thermal shutdown circuit which activates at 150°C (typ).

When this temperature is reached, the device enters a low power standby state. In this state switching remains

off causing the output voltage to fall. Also, the VCON capacitor is discharged to SGND. When the junction

temperature falls back below 130 °C (typ) normal startup occurs and VOUT rises smoothly from 0V. Applications

requiring maximum output current may require derating at elevated ambient temperature. See the Typical

Performance Characteristics section for thermal derating plots for various output voltages.

Application Information

Figure 38. Typical Application Circuit

SETTING THE OUTPUT VOLTAGE

The LMZ10501 provides a fixed 2.35V VREF voltage output. As shown in Figure 38 above, a resistive divider

formed by RT and RB sets the VCON pin voltage level. The VOUT voltage tracks VCON and is governed by the

following relationship:

VOUT = GAIN x VCON

where

•

GAIN is 2.5V/V from VCON to VFB.

(1)

This equation is valid for output voltages between 0.6V and 3.6V and corresponds to VCON voltage between

0.24V and 1.44V, respectively.

RT and RB Selection for Fixed VOUT

The parameters affecting the output voltage setting are the RT, RB, and the product of the VREF voltage x GAIN.

The VREF voltage is typically 2.35V. Since VCON is derived from VREF via RT and RB,

VCON = VREF x RB/ (RB + RT)

(2)

After substitution,

VOUT = VREF x GAIN x RB/ (RB + RT)

(3)

RT = ( GAIN x VREF / VOUT – 1 ) x RB

(4)

The ideal product of GAIN x VREF = 5.875V.

Choose RT to be between 80kΩ and 300kΩ. Then, RB can be calculated using Equation 5 below.

RB = ( VOUT / (5.875V – VOUT) ) x RT

(5)

Note that the resistance of RT should be ≥ 80kΩ. This ensures that the VREF output current loading is not

exceeded and the reference voltage is maintained. The current loading on VREF should not be greater than 30

µA.

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