VIN

VIN

EN

BOOST

SW

FB

GND

VOUT

C3

L1

C2

R1

R2

D1

D2

ON

OFF

D3

C4

R4

C1

R3

LM2736

www.ti.com

SNVS316H – SEPTEMBER 2004 – REVISED DECEMBER 2014

8.2.3 LM2736X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA

Figure 23. LM2736X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA

8.2.3.1 Design Requirements

An alternative method when VIN is greater than 5.5V is to place the zener diode D3 in a shunt configuration. A

small 350 mW to 500 mW 5.1 V zener in a SOT or SOD package can be used for this purpose. A small ceramic

capacitor such as a 6.3 V, 0.1 µF capacitor (C4) should be placed in parallel with the zener diode. When the

internal NMOS switch turns on, a pulse of current is drawn to charge the internal NMOS gate capacitance. The

0.1 µF parallel shunt capacitor ensures that the VBOOST voltage is maintained during this time

8.2.3.2 Detailed Design Procedure

Table 3. Bill of Materials for Figure 23

PART ID

PART VALUE

PART NUMBER

MANUFACTURER

U1

750mA Buck Regulator

LM2736X

TI

C1, Input Cap

10µF, 25V, X7R

C3225X7R1E106M

TDK

C2, Output Cap

22µF, 6.3V, X5R

C3216X5ROJ226M

TDK

C3, Boost Cap

0.01µF, 16V, X7R

C1005X7R1C103K

TDK

C4, Shunt Cap

0.1µF, 6.3V, X5R

C1005X5R0J104K

TDK

D1, Catch Diode

0.4VF Schottky 1A, 30VR

SS1P3L

Vishay

D2, Boost Diode

1VF @ 50mA Diode

1N4148W

Diodes, Inc.

D3, Zener Diode

5.1V 250Mw SOT

BZX84C5V1

Vishay

L1

6.8µH, 1.6A,

SLF7032T-6R8M1R6

TDK

R1

2k

Ω, 1%

CRCW06032001F

Vishay

R2

10k

Ω, 1%

CRCW06031002F

Vishay

R3

100k

Ω, 1%

CRCW06031003F

Vishay

R4

4.12k

Ω, 1%

CRCW06034121F

Vishay

Please refer to Detailed Design Procedures.

8.2.3.3 Application Curves

Please refer to Application Curves.

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