ISL6251 데이터 시트보기 (PDF) - Renesas Electronics

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ISL6251

Low Cost Multi-Chemistry Battery Charger Controller

Renesas Electronics 

ISL6251, ISL6251A

TABLE 2. COMPONENT LIST (Continued)

PARTS

PART NUMBERS AND MANUFACTURER

C3, C7, C9 1F/10V ceramic capacitor, Taiyo Yuden

LMK212BJ105MG

C5

10nF ceramic capacitor

C6

6.8nF ceramic capacitor

C11

3300pF ceramic capacitor

D1

30V/3A Schottky diode, EC31QS03L (optional)

D2, D3 100mA/30V Schottky Diode, Central Semiconductor

D4

8A/30V Schottky rectifier, STPS8L30B (optional)

L

10H/3.8A/26m, Sumida, CDRH104R-100

Q1, Q2 30V/35m, FDS6912A, Fairchild.

Q3

Signal N-channel MOSFET, 2N7002

R1

40m, 1%, LRC-LR2512-01-R040-F, IRC

R2

20m, 1%, LRC-LR2010-01-R020-F, IRC

R3

18, 5%, (0805)

R4

2.2, 5%, (0805)

R5

100k, 5%, (0805)

R6

10k, 5%, (0805)

R7

100, 5%, (0805)

R8, R11 130k, 1%, (0805)

R9

10.2k, 1%, (0805)

R10

4.7, 5%, (0805)

R12

20k, 1%, (0805)

R13

1.87k, 1%, (0805)

Loop Compensation Design

ISL6251, ISL6251A uses constant frequency current mode

control architecture to achieve fast loop transient response. An

accurate current sensing resistor in series with the output

inductor is used to regulate the charge current, and the sensed

current signal is injected into the voltage loop to achieve current

mode control to simplify the loop compensation design. The

inductor is not considered as a state variable for current mode

control and the system becomes single order system. It is much

easier to design a compensator to stabilize the voltage loop than

voltage mode control. Figure 14 shows the small signal model of

the synchronous buck regulator.

PWM Comparator Gain Fm:

The PWM comparator gain Fm for peak current mode control is

given by Equation 19:

M

=

--1---1----

VIN

.

(EQ. 19)

Power Stage Transfer Functions

Transfer function F1(S) from control to output voltage is:

F1 S



vˆ o

dˆ

 Vin

1 S

 esr

S2  S

1



2

o

oQp

Where

 esr



1

RcCo

,

Qp

 Ro

Co , o 

L

1

LCo

(EQ. 20)

Transfer function F2(S) from control to inductor current is:

F2

S



iˆL

dˆ

 Vin

Ro  RL

S2

1 S

z

S

1

,

where

z



1

RoCo

.



2

o

oQp

Current loop gain Ti(S) is expressed as shown in Equation 21:

TiS = 0.25 RTF2SM

(EQ. 21)

where RT is the trans-resistance in current loop. RT is usually

equal to the product of the charging current sensing resistance

and the gain of the current sense amplifier, CA2. For ISL6251,

ISL6251A, RT = 20R1.

The voltage gain with open current loop is:

TvS = KM F1SAVS

(EQ. 22)

Where

K

 VFB

Vo

, VFB is the feedback voltage of the voltage error

amplifier. The Voltage loop gain with current loop closed is given

by Equation 23:

Lv

(

S

)



1

Tv S

 Ti S



(EQ. 23)

If Ti(S)>>1, then it can be simplified as follows:

LVS

=

4----V-----F---B--

VO

---R-----O-----+------R----L------

RT

--1-----+---------------Se------s-------r

1 + --S---P--

AV

S



P



--------1---------

ROCO

(EQ. 24)

From the above equation, it is shown that the system is a single

order system, which has a single pole located at p before the

half switching frequency. Therefore, simple type II compensator

can be easily used to stabilize the system.

FN9202 Rev 3.00

March 13, 2014

Page 16 of 20

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