ADP3026 データシートの表示（PDF） - Analog Devices

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ADP3026

High Efficiency Dual Power Supply Controller

Analog Devices 

Output Undervoltage Protection

Each switching controller has an undervoltage protection

circuit. When the current flowing through the high-side

MOSFET reaches the current limit continuously for eight clock

cycles, and the output voltage is below 20% of the nominal

output voltage, both controllers are latched off and do not

restart until SD or SS3/SS5 is toggled, or until VIN is cycled

below 4.1 V. This feature is disabled during soft start.

Output Overvoltage and Reverse Voltage Protection

Both converter outputs are continuously monitored for

overvoltage. If either output voltage is higher than the nominal

output voltage by more than 20%, both converters’ high-side

gate drivers (DRVH5/3) are latched off; the low-side gate

drivers are latched on and neither restart until SD or SS5/SS3 is

toggled, or until VIN is cycled below 4 V. The low-side gate driver

(DRVL) is kept high when the controller is in off-state and the

output voltage is less than 93% of the nominal output voltage.

Discharging the output capacitors through the main inductor

and low-side N-channel MOSFET causes the output voltage to

ring. This makes the output momentarily go below GND. To

prevent damage to the circuit, use a reverse-biased 1 A Schottky

diode in parallel with the output capacitors to clamp the

negative surge.

Power Good Output (PWRGD)

The ADP3026 provides a PWRGD signal that is used to indicate

to a microprocessor that the ADP3026 output voltages are in

regulation. During startup, the PWRGD pin is held low until the

5 V output is within –3% of its preset voltage. Then, after a time

delay determined by an external timing capacitor connected

from CPOR to GND, PWRGD is actively pulled up to INTVCC

by an external pull-up resistor. The delay is calculated by

Td = 1.2 V ×CCPOR

(2)

1 μA

CPOR can also be used as a manual reset (MR) function. When

the 5 V output is lower than the preset voltage by more than 7%,

PWRGD is immediately pulled low.

APPLICATION INFORMATION

A typical application circuit using the ADP3026 is shown in

Figure 15. Although the component values given in Figure 16

are based on a 5 V @ 4 A/3.3 V @ 4 A design, the ADP3026’s

output drivers are capable of handling output currents

anywhere from less than 1 A to more than 10 A. Throughout

this section, design examples and component values are given

for three different power levels. For simplicity, these levels are

Table 5. Typical Power Level Examples

Input Voltage Range

Switching Output 1

Switching Output 2

Low Power

5.5 V to 25 V

3.3 V/2 A

5 V/2 A

ADP3026

referred to as low power, basic, and extended power. Table 5

shows the input/output specifications for these three levels.

Input Voltage Range

The input voltage range of the ADP3026 is 5.5 V to 25 V. The

converter design is optimized to deliver the best performance

within a 7.5 V to 18 V range, which is the nominal voltage for

three to four cell Li-Ion battery stacks. Voltages above 18 V may

occur under light loads and when the system is powered from

an ac adapter with no battery installed.

Maximum Output Current and MOSFET Selection

The maximum output current for each switching regulator is

limited by sensing the voltage drop between the drain and

source of the high-side MOSFET when it is turned on. A

current sense comparator senses voltage drop between CS5 and

SW5 for the 5 V converter, and between CS3 and SW3 for the

3.3 V converter. The sense comparator threshold is 72 mV when

the programming pin, CLSET, is floating, and 300 mV when

CLSET is connected to ground. Current-limiting is based on

sensing the peak current. Peak current varies with input voltage

and depends on the inductor value. The higher the inductor

ripple current or input voltage, the lower the converter’s

maximum output current at the set current sense amplifier

threshold. The relation between peak inductor and dc output

current is given by

IPEAK

=

IOUT

+ VOUT

× ⎜⎜⎝⎛

VIN(MAX) − VOUT

2 × f × L ×VIN(MAX)

⎟⎟⎠⎞

(3)

At a given current comparator threshold, VTH, and MOSFET

RDS(ON), the maximum inductor peak current is

I PEAK = V TH

(4)

RDS(ON )

Rearranging Equation 2 to solve for IOUT(MAX) gives

I(OUT )MAX

=

V TH

RDS(ON )

−

V

OUT

×

⎜⎜⎝⎛

V

2×

IN (MAX) −

f ×L×V

V

IN

OUT

( MAX )

⎟⎟⎠⎞

(5)

Thus, VTH can be chosen to design the required maximum

output current. It is important to remember that this current

limit circuit is designed to protect against high current or short-

circuit conditions only. This protects the IC and MOSFETs long

enough to allow the output undervoltage protection circuitry to

latch off the supply.

Basic

5.5 V to 25 V

3.3 V/4 A

5 V/4 A

Extended Power

5.5 V to 25 V

3.3 V/10 A

5 V/10 A

Rev. 0 | Page 11 of 20

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