L6725
L6725A
Voltage mode PWM controller
with bootstrap anti-discharging system
Features
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■
■
Input voltage range from 1.8V to 18V
Supply voltage range from 4.5V to 18V
Adjustable output voltage down to 0.6V with
±0.8% accuracy over line voltage and
temperature (0°C~125°C)
Fixed frequency voltage mode control
0% to 100% duty cycle
External input voltage reference
Soft-start and inhibit
Bootstrap anti-discharging system
High current embedded drivers
Predictive anti-cross conduction control
Programmable high-side and low-side R
DS(on)
sense over-current-protection
Sink current capability
Selectable switching frequency 250KHz/
500KHz
Power good and synch available with L6725A
Pre-bias start up capability
Over voltage protection
Thermal shut-down
Package: SO16N
SO16N (Narrow)
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Applications
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Low voltage distributed DC-DC
Graphic cards
Table 1.
Device summary
Order codes
L6725
L6725TR
L6725A
L6725ATR
Package
SO16N
SO16N
SO16N
SO16N
Packing
Tube
Tape & Reel
Tube
Tape & Reel
June 2007
Rev 5
1/32
www.st.com
32
Contents
L6725 - L6725A
Contents
1
Summary description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1
Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1
2.2
Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3
4
5
Pin connections and functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Internal LDO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Bypassing the LDO to avoid the voltage drop with low Vcc . . . . . . . . . . . . . 11
Internal and external references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Soft start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Driver section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Monitoring and protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Hiccup mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2/32
L6725 - L6725A
5.11
5.12
Contents
Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Bootstrap anti-discharging system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.12.1 Fan's power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6
Application details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.1
6.2
6.3
6.4
Inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Output capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Input capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7
L6725 demoboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1
7.2
20A board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5A board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8
9
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3/32
Summary description
L6725 - L6725A
1
Summary description
The device is a flexible high performance PWM buck controller dedicated for low voltage
distributed DC-DC. The input voltage can range from 1.8V to 18V, while the supply voltage can
range from 4.5V to 18V. The output voltage is adjustable down to 0.6V.
High peak current gate drivers provide for fast switching to the external power section, and the
output current can be in excess of 20A. The device is capable to manage minimum on-times
(T
ON
) shorter than 100ns making possible conversions with very low duty cycle and very high
switching frequency. In order to guarantee a real overcurrent protection, also with very narrow
T
ON
, the current sense is realized both on the high-side and low-side MOSFETs. When
necessary, two different current limit protections can be externally set through an external
resistor. The device can sink current after the soft-start phase while, during the soft-start, the
sink mode capability is disabled in order to allow a proper start-up also in pre-biased output
voltage conditions. Other features are over-voltage-protection and thermal shutdown.
1.1
Functional description
Figure 1.
Block diagram
Vcc=4.5V-14V
Vcc = 14V - 18V
Vin = 14V - 18V
Vin=1.8V-14V
OCL
OCH
VCCDR
BOOT
LDO
SS
Monitor
Protection and Ref
HGATE
OSC
EAREF
-
PHASE
V
OUT
L6725
PGOOD
LGATE
+
-
-
0.6V
+
PWM
SYNCH
+
PGND
E/A
-
GND
FB
COMP
4/32
L6725 - L6725A
Electrical data
2
2.1
Table 2.
Electrical data
Maximum rating
Absolute maximum ratings
Parameter
V
CC
to GND and PGND, OCH
Value
-0.3 to 20
0 to 6
0 to V
BOOT
- V
PHASE
BOOT
PHASE
V
PHASE
PHASE Spike, transient < 50ns (F
SW
= 500KHz)
SS, FB, EAREF, OCL, LGATE, COMP, V
CCDR
OCH Pin
OTHER PINS
Maximum withstanding voltage range
Test Condition: CDF-AEC-Q100-002 "Human Body Model"
Acceptance Criteria: "Normal Performance"
-0.3 to 26
-1 to 20
-3
+24
-0.3 to 6
±1500
V
±2000
V
V
Unit
V
\
V
V
Symbol
V
CC
V
BOOT -
V
PHASE
Boot voltage
V
HGATE -
V
PHASE
V
BOOT
2.2
Table 3.
Thermal data
Thermal data
Description
Max. thermal resistance junction to ambient
Storage temperature range
Junction operating temperature range
Ambient operating temperature range
Value
50
-40 to 150
-40 to 125
-40 to +85
Unit
°C/W
°C
°C
°C
Symbol
R
thJA(1)
T
STG
T
J
T
A
1. Package mounted on demoboard
5/32
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