LTC4090(RevA) 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

제조사

LTC4090
(Rev.:RevA)

USB Power Manager with 2A High Voltage Bat-Track Buck Regulator

Linear Technology 

LTC4090/LTC4090-5

APPLICATIONS INFORMATION

minimum switch-off time (~150ns). These equations show

that duty cycle range increases when switching frequency

is decreased.

A good choice of switching frequency should allow ad-

equate input voltage range (see next section) and keep

the inductor and capacitor values small.

HVIN Input Voltage Range

The maximum input voltage range for the LTC4090/

LTC4090-5 applications depends on the switching fre-

quency, the Absolute Maximum Ratings of the VHVIN and

BOOST pins, and the operating mode.

The high voltage switching regulator can operate from

input voltages up to 36V, and safely withstand input volt-

ages up to 60V. Note that while VHVIN > 41.5V (typical),

the LTC4090/LTC4090-5 will stop switching, allowing the

output to fall out of regulation.

While the high voltage regulator output is in start-up,

short-circuit, or other overload conditions, the switching

frequency should be chosen according to the following

discussion.

For safe operation at inputs up to 60V the switching fre-

quency must be low enough to satisfy VHVIN(MAX) ≥ 45V

according to the following equation. If lower VHVIN(MAX)

is desired, this equation can be used directly.

VHVIN(MAX)

=

VHVOUT + VD

fSW • tON(MIN)

–

VD

+

VSW

where VHVIN(MAX) is the maximum operating input voltage,

VHVOUT is the high voltage regulator output voltage, VD is

the catch diode drop (~0.5V), VSW is the internal switch

drop (~0.5V at max load), fSW is the switching frequency

(set by RT), and tON(MIN) is the minimum switch-on time

(~150ns). Note that a higher switching frequency will de-

press the maximum operating input voltage. Conversely,

a lower switching frequency will be necessary to achieve

safe operation at high input voltages.

If the output is in regulation and no short-circuit, start-

up, or overload events are expected, then input voltage

transients of up to 60V are acceptable regardless of the

switching frequency. In this mode, the LTC4090/LTC4090-5

may enter pulse skipping operation where some switch-

ing pulses are skipped to maintain output regulation. In

this mode the output voltage ripple and inductor current

ripple will be higher than in normal operation. Above 41.5V,

switching will stop.

The minimum input voltage is determined by either the high

voltage regulator’s minimum operating voltage of ~6V or by

its maximum duty cycle (see equation in previous section).

The minimum input voltage due to duty cycle is:

VHVIN(MIN)

=

VHVOUT + VD

1− fSWtOFF(MIN)

−

VD

+

VSW

where VHVIN(MIN) is the minimum input voltage, and

tOFF(MIN) is the minimum switch off time (150ns). Note

that higher switching frequency will increase the minimum

input voltage. If a lower dropout voltage is desired, a lower

switching frequency should be used.

Inductor Selection and Maximum Output Current

A good choice for the inductor value is L = 6.8μH (assum-

ing a 800kHz operating frequency). With this value the

maximum load current will be ~2.4A. The RMS current

rating of the inductor must be greater than the maximum

load current and its saturation current should be about

30% higher. Note that the maximum load current will be

programmed charge current plus the largest expected

application load current. For robust operation in fault

conditions, the saturation current should be ~3.5A. To

keep efficiency high, the series resistance (DCR) should

be less than 0.1Ω. Table 2 lists several vendors and types

that are suitable.

Table 2. Inductor Vendors

VENDOR URL

Murata www.murata.com

TDK

www.componenttdk.com

Toko www.toko.com

Sumida www.sumida.com

PART SERIES

LQH55D

SLF7045

SLF10145

D62CB

D63CB

D75C

D75F

CR54

CDRH74

CDRH6D38

CR75

TYPE

Open

Shielded

Shielded

Shielded

Shielded

Shielded

Open

Open

Shielded

Shielded

Open

4090fa

19

Share Link: