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LTC1430

High Power Step-Down Switching Regulator Controller

Linear Technology 

LTC1430

APPLICATIO S I FOR ATIO

OS-CON part number 10SA220M (220µF/10V) capacitors

feature 2.3A allowable ripple current at 85°C and 0.035Ω

ESR; three in parallel at the input and six at the output will

meet the above requirements.

Input Supply Considerations/Charge Pump

The 16-lead LTC1430 requires four supply voltages to

operate: PVCC for the main power input, PVCC1 and PVCC2

for MOSFET gate drive and a clean, low ripple VCC for the

LTC1430 internal circuitry (Figure 6). In many applica-

tions, PVCC and PVCC2 can be tied together and fed from

a common high power supply, provided that the supply

voltage is high enough to fully enhance the gate of external

MOSFET M2. This can be the 5V system supply if a logic

level MOSFET is used for M2. VCC can usually be filtered

with an RC from this same high power supply; the low

quiescent current (typically 350µA) allows the use of

relatively large filter resistors and correspondingly small

filter capacitors. 100Ω and 4.7µF usually provide ad-

equate filtering for VCC.

VCC

PVCC2 PVCC1

PVCC

INTERNAL

CIRCUITRY

G1

M1

L1

G2

M2

VOUT

+

COUT

LTC1430 (16-LEAD)

LTC1430 • F06

Figure 6. 16-Lead Power Supplies

The 8-lead versions of the LTC1430 have the PVCC2 and

VCC pins tied together inside the package (Figure 7). This

pin, brought out as VCC/PVCC2, has the same low ripple

requirements as the 16-lead part, but must also be able to

supply the gate drive current to M2. This can be obtained

by using a larger RC filter from the PVCC pin; 22Ω and 10µF

work well here. The 10µF capacitor must be VERY close to

the part (preferably right underneath the unit) or output

regulation may suffer.

For both versions of the LTC1430, PVCC1 must be higher

than PVCC by at least one external MOSFET VGS(ON) to fully

enhance the gate of M1. This higher voltage can be

provided with a separate supply (typically 12V) which

should power up after PVCC, or it can be generated with a

simple charge pump (Figure 4). The charge pump consists

of a 1N4148 diode from PVCC to PVCC1 and a 0.1µF

capacitor from PVCC1 to the switching node at the drain of

M2. This circuit provides 2PVCC – VF to PVCC1 while M1 is

ON and PVCC – VF while M1 is OFF where VF is the ON

voltage of the 1N4148 diode. Ringing at the drain of M2

can cause transients above 2PVCC at PVCC1; if PVCC is

higher than 7V, a 12V zener diode should be included from

PVCC1 to PGND to prevent transients from damaging the

circuitry at PVCC2 or the gate of M1.

More complex charge pumps can be constructed with the

16-lead versions of the LTC1430 to provide additional

voltages for use with standard threshold MOSFETs or very

low PVCC voltages. A tripling charge pump (Figure 5) can

provide 2PVCC and 3PVCC voltages. These can be con-

nected to PVCC2 and PVCC1 respectively, allowing stan-

dard threshold MOSFETs to be used with 5V at PVCC or 5V

logic level threshold MOSFETs to be used with 3.3V at

PVCC. VCC can be driven from the same potential as PVCC2,

allowing the entire system to run from a single 3.3V

supply. Tripling charge pumps require the use of Schottky

diodes to minimize forward drop across the diodes at

start-up. The tripling charge pump circuit will tend to

rectify any ringing at the drain of M2 and can provide well

more than 3PVCC at PVCC1; all tripling (or higher multiply-

ing factor) circuits should include a 12V zener clamp diode

DZ to prevent overvoltage at PVCC1.

VCC/PVCC2

PVCC1

PVCC

INTERNAL

CIRCUITRY

LTC1430 (8-LEAD)

G1

M1

L1

G2

M2

VOUT

+

COUT

LTC1430 • F07

Figure 7. 8-Lead Power Supplies

10

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