L6910
L6910A
ADJUSTABLE STEP DOWN CONTROLLER
WITH SYNCHRONOUS RECTIFICATION
1
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FEATURES
OPERATING SUPPLY VOLTAGE FROM 5V
TO 12V BUSES
UP TO 1.3A GATE CURRENT CAPABILITY
ADJUSTABLE OUTPUT VOLTAGE
N-INVERTING E/A INPUT AVAILABLE
0.9V ±1.5% VOLTAGE REFERENCE
VOLTAGE MODE PWM CONTROL
VERY FAST LOAD TRANSIENT RESPONSE
0% TO 100% DUTY CYCLE
POWER GOOD OUTPUT
OVERVOLTAGE PROTECTION
HICCUP OVERCURRENT PROTECTION
200kHz INTERNAL OSCILLATOR
OSCILLATOR EXTERNALLY ADJUSTABLE
FROM 50kHz TO 1MHz
SOFT START AND INHIBIT
PACKAGES: SO-16 & HTSSOP16
Figure 1. Packages
SO-16 (Narrow)
HTSSOP16 (Exposed Pad)
Table 1. Order Codes
Part Number
L6910
L6910TR
L6910A
L6910ATR
Package
SO-16
SO-16 in Tape & Reel
HTSSOP16
HTSSOP16 in Tape & Reel
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APPLICATIONS
SUPPLY FOR MEMORIES AND TERMI-
NATIONS
COMPUTER ADD-ON CARDS
LOW VOLTAGE DISTRIBUTED DC-DC
MAG-AMP REPLACEMENT
3
DESCRIPTION
The device is a pwm controller for high performance
Figure 2. Block Diagram
dc-dc conversion from 3.3V, 5V and 12V buses.
The output voltage is adjustable down to 0.9V;
higher voltages can be obtained with an external
voltage divider.
High peak current gate drivers provide for fast switch-
ing to the external power section, and the output
current can be in excess of 20A.
The device assures protections against load overcur-
rent and overvoltage. An internal crowbar is also pro-
vided turning on the low side mosfet as long as the
over-voltage is detected. In case of over-current de-
tection, the soft start capacitor is discharged and the
system works in HICCUP mode.
V
in
5V to 12V
VCC
OCSET
PGOOD
VREF
SS
MONITOR
PROTECTION
& REF
BOOT
UGATE
V
O
OSC
RT
OSC
PWM
-
+
BOOT
E/A
EAREF
300K
+
-
LGATE
PGND
GND
VFB
COMP
D03IN1509
May 2005
Rev. 9
1/29
L6910 - L6910A
Table 2. Absolute Maximum Ratings
Symbol
Vcc
V
BOOT
-
V
PHASE
V
HGATE
-
V
PHASE
OCSET, LGATE, PHASE
SS, FB, PGOOD, VREF, EAREF, RT
COMP
T
j
T
stg
P
tot
Junction Temperature Range
Storage temperature range
Maximum power dissipation at Tamb = 25°C
Vcc to GND, PGND
Boot Voltage
Parameter
Value
15
15
15
-0.3 to Vcc+0.3
7
6.5
-40 to 150
-40 to 150
1
Unit
V
V
V
V
V
V
°C
°C
W
Table 3. Thermal Data
Symbol
R
th j-amb
Parameter
Thermal Resistance Junction to Ambient
SO-16
120
HTSSOP16
110
HTSSOP16 (*)
50
Unit
°C/W
(*) Device soldered on 1 S2P PC board
Figure 3. Pins Connection (Top view)
VREF
OSC
OCSET
SS/INH
COMP
FB
GND
EAREF
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
D03IN1510
N.C.
VCC
LGATE
PGND
BOOT
HGATE
PHASE
PGOOD
VREF
OSC
OCSET
SS/INH
N.C.
COMP
FB
GND
1
2
3
4
5
6
7
8
D03IN1511
16
15
14
13
12
11
10
9
VCC
LGATE
PGND
BOOT
HGATE
PHASE
PGOOD
EAREF
2/29
L6910 - L6910A
Table 4. Pins Function
SO
1
HTSSOP
1
Name
VREF
Description
Internal 0.9V ±1.5% reference is available for external regulators or for the internal error
amplifier (connecting this pin to EAREF) if external reference is not available.
A minimum 1nF capacitor is required.
If the pin is forced to a voltage lower than 70%, the device enters the hiccup mode.
Oscillator switching frequency pin. Connecting an external resistor (R
T
) from this pin to
GND, the external frequency is increased according to the equation:
4.94
⋅
10
f
OSC,RT
=
200KHz
+ ------------------------
-
R
T
(
KΩ
)
Connecting a resistor (R
T
) from this pin to Vcc (12V), the switching frequency is reduced
according to the equation:
4.306
⋅
10
f
OSC,RT
=
200KHz
– ----------------------------
-
R
T
(
KΩ
)
If the pin is not connected, the switching frequency is 200KHz.
The voltage at this pin is fixed at 1.23V. Forcing a 50µA current into this pin, the built in
oscillator stops to switch.
In Over Voltage condition this pin goes over 3V until that conditon is removed.
3
3
OCSET
A resistor connected from this pin and the upper Mos Drain sets the current limit
protection.
The internal 200µA current generator sinks a constant current through the external
resistor. The Over-Current threshold is due to the following equation:
I
OCSET
⋅
R
OCSET
I
P
= ---------------------------------------------
-
R
DSon
The soft start time is programmed connecting an external capacitor from this pin and
GND. The internal current generator forces through the capacitor 10µA.
This pin can be used to disable the device forcing a voltage lower than 0.4V
This pin is connected to the error amplifier output and is used to compensate the voltage
control feedback loop.
This pin is connected to the error amplifier inverting input and is used to compensate the
voltage control feedback loop.
Connected to the output resistor divider, if used, or directly to Vout, it manages also over-
voltage conditions and the PGOOD signal
All the internal references are referred to this pin. Connect it to the PCB signal ground.
Error amplifier non-inverting input. Connect to this pin an external reference (from 0.9V to
3V) for the PWM regulation or short it to VREF pin to use the internal reference.
If this pin goes under 650mV (typ), the device shuts down.
7
6
2
2
OSC
4
4
SS/INH
5
6
6
7
COMP
FB
7
8
8
9
GND
EAREF
9
10
10
11
PGOOD This pin is an open collector output and it is pulled low if the output voltage is not within the
above specified thresholds. If not used it may be left floating.
PHASE
This pin is connected to the source of the upper mosfet and provides the return path for the
high side driver. This pin monitors the drop across the upper mosfet for the current limit
together with OCSET.
High side gate driver output.
Bootstrap capacitor pin. Through this pin is supplied the high side driver and the upper
mosfet. Connect through a capacitor to the PHASE pin and through a diode to Vcc
(cathode vs. boot).
Power ground pin. This pin has to be connected closely to the low side mosfet source in
order to reduce the noise injection into the device
This pin is the lower mosfet gate driver output
Device supply voltage. The operative supply voltage ranges is from 5V to 12V.
DO NOT CONNECT V
IN
TO A VOLTAGE GREATER THAN V
CC
.
This pin is not internally bonded. It may be left floating or connected to GND.
11
12
12
13
HGATE
BOOT
13
14
15
16
14
5
16
5
PGND
LGATE
VCC
N.C.
3/29
L6910 - L6910A
Table 5. Electrical Characteristics
(V
cc
= 12V, T
J
=25°C unless otherwise specified)
Symbol
Parameter
V
cc
SUPPLY CURRENT
Icc
Vcc Supply current
POWER-ON
Turn-On Vcc threshold
Turn-Off Vcc threshold
Rising V
OCSET
threshold
Turn On EAREF threshold
SOFT START AND INHIBIT
Iss
Soft start Current
S.S. current in INH condition
OSCILLATOR
f
OSC
Initial Accuracy
f
OSC,RT
Total Accuracy
Test Condition
OSC = open; SS to GND
VOCSET = 4V
VOCSET = 4V
VOCSET = 4V
SS = 2V
SS = 0 to 0.4V
OSC = OPEN
OSC = OPEN; T
j
= 0° to 125°
16 KΩ < R
T
to GND < 200 KΩ
6
Min
4
4.0
3.8
Typ
7
4.3
4.1
1.24
650
10
35
200
Max
9
4.6
4.4
1.4
750
14
60
220
230
15
1.9
V
OUT
= V
FB
; V
EAREF
= V
REF
C
REF
= 1nF; I
REF
= 0 to 100µA
C
REF
= 1nF; T
J
= 0 to 125°C
V
EAREF
= 3V
Vs. GND
V
FB
= 0V to 3V
0.8
0.5
70
COMP = 10pF
V
BOOT
- V
PHASE
= 12V
V
HGATE
- V
PHASE
= 6V
V
BOOT
- V
PHASE
= 12V
Vcc = 12V; V
LGATE
= 6V
Vcc = 12V
PHASE connected to GND
V
OCSET
= 4V
V
FB
Rising
V
FB
> OVP Trip
V
FB
Rising
V
FB
Falling
Upper and Lower threshold
I
PGOOD
= -4mA
V
PGOOD
= 6V
15
108
88
90
170
200
117
30
110
90
2
0.4
0.2
1
112
92
0.9
1
85
10
10
1.3
2
1.1
1.5
3
210
230
120
4
0.886
0.886
-2
10
300
0.01
0.5
3
4
0.900
0.900
0.913
0.913
+2
Unit
mA
V
V
V
mV
µA
µA
KHz
kHz
%
V
V
V
%
µA
kΩ
µA
V
V
dB
MHz
V/µs
A
Ω
A
Ω
ns
µA
%
mA
%
%
%
V
µA
180
170
-15
∆Vosc
Ramp amplitude
REFERENCE
V
OUT
Output Voltage Accuracy
V
REF
V
REF
Reference Voltage
Reference Voltage
ERROR AMPLIFIER
I
EAREF
N.I. bias current
I
FB
V
CM
V
COMP
G
V
EAREF Input Resistance
I.I. bias current
Common Mode Voltage
Output Voltage
Open Loop Voltage Gain
GBWP Gain-Bandwidth Product
SR
Slew-Rate
GATE DRIVERS
I
HGATE
High Side
Source Current
R
HGATE
I
LGATE
R
LGATE
High Side
Sink Resistance
Low Side Source Current
Low Side Sink Resistance
Output Driver Dead Time
PROTECTIONS
I
OCSET
OCSET Current Source
Over Voltage Trip (V
FB
/ V
EAREF
)
I
OSC
OSC Sourcing Current
POWER GOOD
Upper Threshold (V
FB
/ V
EAREF
)
Lower Threshold (V
FB
/ V
EAREF
)
Hysteresis (V
FB
/ V
EAREF
)
V
PGOOD
I
PGOOD
PGOOD Voltage Low
Output Leakage Current
4/29
L6910 - L6910A
4
DEVICE DESCRIPTION
The device is an integrated circuit realized in BCD technology. The controller provides complete con-
trol logic and protection for a high performance step-down DC-DC converter. It is designed to drive N
Channel Mosfets in a synchronous-rectified buck topology. The output voltage of the converter can be
precisely regulated down to 900mV with a maximum tolerance of ±1.5% when the internal reference is
used (simply connecting together EAREF and VREF pins). The device allows also using an external
reference (0.9V to 3V) for the regulation. The device provides voltage-mode control with fast transient
response. It includes a 200kHz free-running oscillator that is adjustable from 50kHz to 1MHz. The er-
ror amplifier features a 10MHz gain-bandwidth product and 10V/µs slew rate that permits to realize
high converter bandwidth for fast transient performance. The PWM duty cycle can range from 0% to
100%. The device protects against over-current conditions entering in HICCUP mode. The device
monitors the current by using the r
DS(ON)
of the upper MOSFET(s) that eliminates the need for a cur-
rent sensing resistor. The device is available in SO16 narrow package.
4.1 Oscillator
The switching frequency is internally fixed to 200kHz. The internal oscillator generates the triangular waveform
for the PWM charging and discharging with a constant current an internal capacitor. The current delivered to the
oscillator is typically 50µA (F
sw
= 200KHz) and may be varied using an external resistor (R
T
) connected between
OSC pin and GND or V
CC
. Since the OSC pin is maintained at fixed voltage (typ. 1.235V), the frequency is var-
ied proportionally to the current sunk (forced) from (into) the pin.
In particular connecting R
T
vs. GND the frequency is increased (current is sunk from the pin), according to the
following relationship:
6
4.94
⋅
10
f
OSC,RT
=
200KHz
+ -------------------------
R
T
(
KΩ
)
Connecting R
T
to V
CC
= 12V or to V
CC
= 5V the frequency is reduced (current is forced into the pin), according
to the following relationships:
4.306
⋅
10
f
OSC,RT
=
200KHz
– ----------------------------
-
R
T
(
KΩ
)
15
⋅
10
f
OSC,RT
=
200KHz
– ---------------------
R
T
(
KΩ
)
6
7
V
CC
= 12V
V
CC
= 5V
Switching frequency variation vs. RT are repeated in Fig. 4.
Note that forcing a 50µA current into this pin, the device stops switching because no current is delivered to the
oscillator.
Figure 4.
10000
1000
Resistance [kOhm]
100
10
RT to GND
RT to VCC=12V
RT to VCC=5V
10
100
1000
Frequency [kHz]
5/29
