MAX17005AETP 查看數據表（PDF） - Maxim Integrated

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MAX17005AETP

1.2MHz, Low-Cost, High-Performance Chargers

Maxim Integrated 

1.2MHz, Low-Cost,

High-Performance Chargers

CC Loop Compensation

The simplified schematic in Figure 7 is sufficient to

describe the operation of the controller’s voltage loop,

CC. The required compensation network is a pole-zero

pair formed with CCC and RCC. The zero is necessary

to compensate the pole formed by the output capacitor

and the load. RESR is the equivalent series resistance

(ESR) of the charger output capacitor (COUT). RL is the

equivalent charger output load, where RL = ΔVBATT/

ΔICHG. The equivalent output impedance of the GMV

amplifier, ROGMV, is greater than 10MΩ. The voltage-

amplifier transconductance, GMV = 0.125μA/mV. The

DC-DC converter transconductance is dependent upon

charge current-sense resistor RS2:

GMOUT

BATT

RESR

RL

COUT

CC

GMV

RCC

CCC

ROGMV

VCTL

GMOUT

=

1

ACSI × RS2

where ACSI = 20, and RS2 = 10mΩ in the typical appli-

cation circuits, so GMOUT = 5A/V.

The loop transfer function is given by:

LTF = GMOUT × RL × GMV × ROGMV

× (1+ sCOUT × RESR)(1+ sCCC × RCC)

(1+ sCCC × ROGMV )(1+ sCOUT × RL )

The poles and zeros of the voltage-loop transfer function

are listed from lowest frequency to highest frequency in

Table 2.

Near crossover, CCC is much lower impedance than

ROGMV. Since CCC is in parallel with ROGMV, CCC domi-

nates the parallel impedance near crossover. Additionally,

RCC is much higher impedance than CCC and dominates

the series combination of RCC and CCC, so:

ROGMV × (1+

(1+ sCCC

sCCC × RCC)

× ROGMV )

≅

RCC

COUT is also much lower impedance than RL near

crossover so the parallel impedance is mostly capaci-

tive and:

RL

≅1

(1+ sCOUT × RL ) sCOUT

Figure 7. CC Loop Diagram

Table 2. CC Loop Poles and Zeros

NAME

CCV Pole

CCV Zero

EQUATION

fP _ CV

=

1

2πROGMV

× CCC

fZ _ CV

=

1

2πRCC × CCC

DESCRIPTION

Lowest frequency pole created by CCV and GMV’s finite output resistance.

Voltage-loop compensation zero. If this zero is at the same frequency or lower

than output pole fP_OUT, the loop-transfer function approximates a single-pole

response near the crossover frequency. Choose CCV to place this zero at

least one decade below crossover to ensure adequate phase margin.

Output

Pole

Output

Zero

fP _ OUT

=

2πRL

1

× COUT

fZ _ OUT

=

1

2πRESR ×

COUT

Output pole formed with the effective load resistance RL and the output

capacitance COUT. RL influences the DC gain but does not affect the stability

of the system or the crossover frequency.

Output ESR Zero. This zero can keep the loop from crossing unity gain if

fZ_OUT is less than the desired crossover frequency; therefore, choose a

capacitor with an ESR zero greater than the crossover frequency.

______________________________________________________________________________________ 17

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