L6997
STEP DOWN CONTROLLER
FOR LOW VOLTAGE OPERATIONS
FEATURES
s
FROM 3V TO 5.5V V
CC
RANGE.
s
MINIMUM OUTPUT VOLTAGE AS LOW AS
0.6V.
s
1V TO 28V INPUT VOLTAGE RANGE.
s
CONSTANT ON TIME TOPOLOGY ALLOWS.
OPERATION WITH VERYLOW AND HIGH
DUTY CYCLES.
s
VERY FAST LOAD TRANSIENTS.
s
0.6V, ±1% VREF.
s
SELECTABLE SINKING MODE.
s
LOSSLESS CURRENT LIMIT, AVAILABLE
ALSO IN SINKING MODE
s
REMOTE SENSING.
s
OVP,UVP LATCHED PROTECTIONS.
s
600µA TYP QUIESCENT CURRENT.
s
POWER GOOD AND OVP SIGNALS.
s
PULSE SKIPPING AT LIGTH LOADS.
s
94% EFFICIENCY FROM 3.3V TO 2.5V.
APPLICATIONS
s
NETWORKING.
s
DC/DC MODULES.
s
DISTRIBUTED POWER.
s
MOBILE APPLICATIONS.
s
CHIP SET, CPU, DSP AND MEMORIES SUPPLY.
MINIMUM COMPONENT COUNT APPLICATION
3.3V
Rin2
Rin1
TSSOP20
ORDERING NUMBERS: L6997D
L6997DTR
DESCRIPTION
The device is a high efficient solution for networking
dc/dc modules and mobile application compatible
with 3.3V bus and 5V bus.
It's able to regulate an output voltage as low as 0.6V.
The constant on time topology assures fast load tran-
sient response. The embedded voltage feed-forward
provides nearly constant switching frequency opera-
tion.
An integrator can be introduced in the control loop to
reduce the static output voltage error.
The remote sensing improves the static and dynamic
regulation, recovering the wires voltage drop.
Pulse skipping technique reduces power consump-
tion at light loads. Drivers current capability allows
output currents in excess of 20A.
Cin
VCC
VDR
OSC
BOOT
HGATE
HS
Cboot
L
PHASE
PGOOD
OVP
LGATE
LS
DS
Ro2
Ro1
Cout
Dboot
0.6V
L6997
ILIM
Rilim
PGND
GND
GNDSENSE
SS
Css
VSENSE
INT
VFB
SHDN
Vref
Cvref
April 2003
1/23
L6997
ABSOLUTE MAXIMUM RATINGS
Symbol
V
CC
V
DR
V
CC
to GND
V
DR
to GND
HGATE and BOOT, to PHASE
HGATE and BOOT, to PGND
V
PHASE
PHASE
LGATE to PGND
ILIM, VFB, VSENSE, NOSKIP, SHDN, PGOOD, OVP, VREF, INT,
GND
SENSE
to GND
P
tot
T
stg
Power dissipation at T
amb
= 25°C
Storage temperature range
Parameter
Value
-0.3 to 6
-0.3 to 6
-0.3 to 6
-0.3 to 36
-0.3-to 30
-0.3 to V
DR
+0.3
-0.3 to V
CC
+0.3
1
-40 to 150
Unit
V
V
V
V
V
V
V
W
°C
THERMAL DATA
Symbol
R
th j-amb
T
j
Parameter
Thermal Resistance Junction to Ambient
Junction operating temperature range
Value
125
-40 to 125
Unit
°C/W
°C
PIN CONNECTION
(Top View)
NOSKIP
GNDSENSE
INT
VSENSE
VCC
GND
VREF
VFB
OSC
SS
1
2
3
4
5
6
7
8
9
10
TSSOP20
20
19
18
17
16
15
14
13
12
11
BOOT
HGATE
PHASE
VDR
LGATE
PGND
PGOOD
OVP
SHDN
ILIM
PIN FUNCTION
N°
1
2
3
4
5
6
7
Name
GNDSE
NSE
INT
VSENS
E
V
CC
GND
VREF
Remote ground sensing pin
Integrator output. Short this pin to VFB pin and connect it via a capacitor to V
OUT
to insert the
integrator in the control loop. If the integrator is not used, short this pin to VREF.
This pin must be connected to the remote output voltage to detect overvoltage and undervoltage
conditions and to provide integrator feedback input.
IC Supply Voltage.
Signal ground
0.6V voltage reference. Connect max. a 10nF ceramic capacitor between this pin and ground.
This pin is capable to source or sink up to 250uA
Description
NOSKIP Connect to V
CC
to force continuous conduction mode and sink mode.
2/23
L6997
PIN FUNCTION
(continued)
N°
8
9
10
11
12
13
14
15
16
17
18
19
20
Name
VFB
OSC
SS
ILIM
SHDN
OVP
PGOOD
PGND
LGATE
V
DR
PHASE
HGATE
BOOT
Description
PWM comparator feedback input. Short this pin to INT pin when using the integrator function, or
to VSENSE pin without integrator.
Connect this pin to the input voltage through a voltage divider in order to provide the feed-
forward function. It cannot be left floating.
Soft start pin. A 5µA constant current charges an external capacitor which value sets the soft-
start time.
An external resistor connected between this pin and GND sets the current limit threshold.
Shutdown. When connected to GND the device and the drivers are OFF. It cannot be left floating.
Open drain output. During the over voltage condition it is pulled up by an external resistor.
Open drain output. During the soft start and in case of output voltage fault it is low. It is pulled up
by external resistor.
Low Side driver ground.
Low Side driver output.
Low Side driver supply.
Return path of the High Side driver.
High side MOSFETS driver output.
Bootstrap capacitor pin. High Side driver is supplied through this pin.
ELECTRICAL CHARACTERISTICS
(V
CC
= V
DR
= 3.3V; T
amb
= 0°C to 85°C unless otherwise specified)
Symbol
SUPPLY SECTION
Vin
V
CC
,
V
DR
V
CC
Turn-onvoltage
Turn-off voltage
Hysteresis
IqV
DR
IqVcc
Quiescent Current Drivers
Device Quiescent current
VFB > VREF
VFB > VREF
Input voltage range
Vout=Vref Fsw=110Khz Iout=1A
1
3
2.86
2.75
90
7
400
20
600
28
5.5
2.97
2.9
V
V
V
V
mV
µA
µA
V
0.6
SHDN to GND
SHDN to GND
1
5
15
V
µA
µA
µA
mV
µA
mV
µA
Parameter
Test Condition
Min.
Typ.
Max.
Unit
SHUTDOWN SECTION
SHDN
Device On
Device Off
I
SH
V
DR
I
SH
V
CC
Drivers shutdown current
Devices shutdown current
1.2
SOFT START SECTION
I
SS
Soft Start current
Active Soft start and voltage
CURRENT LIMIT AND ZERO CURRENT COMPARATOR
ILIM input bias current
Zero Crossing Comparator offset
Phase-gnd
DK
ILIM
Current limit factor
R
ILIM
= 2KΩ to 200KΩ
4.6
-2
1.6
1.8
5
5.4
2
2
V
SS
= 0.4V
4
300
400
6
500
3/23
L6997
ELECTRICAL CHARACTERISTICS
(continued)
(V
CC
= V
DR
= 3.3V; T
amb
= 0°C to 85°C unless otherwise specified)
Symbol
ON TIME
Ton
On time duration
V
REF
=V
SENSE OSC
=125mV
V
REF
=V
SENSE OSC
=250mV
V
REF
=V
SENSE OSC
=500mV
OFF TIME
T
OFFMIN
Minimum off time
K
OSC
/T
OFFMIN
VOLTAGE REFERENCE
VREF
Voltage Accuracy
0µA < I
REF
< 100µA
0.594
0.6
0.606
V
OSC=250mV
0.3
600
0.33
ns
720
370
210
800
420
240
880
470
270
ns
ns
ns
Parameter
Test Condition
Min.
Typ.
Max.
Unit
PWM COMPARATOR
Input voltage offset
I
FB
Input Bias Current
-2
20
+2
mV
nA
INTEGRATOR
INT
INT
Over Voltage Clamp
Under Voltage Clamp
Integrator Input Offset Voltage
V
SENSE
-V
REF
I
VSENSE
Input Bias Current
V
SENSE
= V
CC
V
SENSE
= GND
0.62
0.45
-4
20
0.75
0.55
0.88
0.65
-4
V
V
mV
nA
GATE DRIVERS
High side rise time
High side fall time
Low side rise time
Low side fall time
P
GOOD
UVP/OVP PROTECTIONS
OVP
UVP
PGOOD
PGOOD
V
PGOOD
Over voltage threshold
Under voltage threshold
Upper threshold
(V
SENSE
-V
REF
)
Lower threshold
(V
SENSE
-V
REF
)
V
SENSE
rising
V
SENSE
falling
I
Sink
=2mA
with respect to V
REF
118
67
110
85
121
70
112
88
0.2
124
73
116
91
0.4
%
%
%
%
V
V
DR
=3.3V; C=7nF
HGATE - PHASE from 1 to 3V
V
DR
=3.3V; C=14nF
LGATE from 1 to 3V
50
50
50
50
90
100
90
90
ns
ns
ns
ns
4/23
Vcc
SHDN
+
VSENSE
1.12 VREF
-
undervoltage comparator
-
VSENSE
0.6 VREF
IC enable
pgood comparators
+
-
VSENSE
VCC
VSENSE
0.925 VREF
HGATE
BOOT
V(LGATE)<0.5V
comp
+
-
LS and HS anti-cross-conduction comparators
1.075 VREF
soft-start
control
S
R
+
PGOOD
OVP
overvoltage comparator
VCC
GND
SS
5 uA
ILIM
power management
V
IN
R
Q
V(PHASE)<0.2V
comp
PHASE
level shifter
HS driver
Figure 1. Functional & Block Diagram
positive current limit
comparator
Toff min
delay
S
V
OUT
PHASE
Ton min
one-shot
Q
LS driver
-
+
VDR
0.05
R
Ton
one-shot
-
+
LGATE
VREF
S
VSENSE
OSC
+
PGND
FB
-
pwm comparator
Ton= Kosc V(VSENSE)/V(OSC)
S
Q
INT
+
-
Ton
one-shot
Gm
HS control
-
+
R
VREF
SENSEGND
no-skip
mode
no-skip
mode
+
-
+
-
Ton= Kosc V(VSENSE)/V(OSC)
OSC
bandgap
PHASE
-
zero-cross comparator
+
PHASE
negative current limit
comparator
1.236V
VREF
0.6V
1.416
0.05
ILIM
Reference chain
NOSKIP
LS control
VSENSE
OSC
V
IN
VREF
VSENSE
L6997
5/23
